[PATCH v3 00/12] fuse: optimize scatter-gather direct IO

[PATCH v3 00/12] fuse: optimize scatter-gather direct IO

[Maxim Patlasov]

Hi,

Existing fuse implementation processes scatter-gather direct IO in suboptimal
way: fuse_direct_IO passes iovec[] to fuse_loop_dio and the latter calls
fuse_direct_read/write for each iovec from iovec[] array. Thus we have as many
submitted fuse-requests as the number of elements in iovec[] array. This is
pure waste of resources and affects performance negatively especially for the
case of many small chunks (e.g. page-size) packed in one iovec[] array.

The patch-set amends situation in a natural way: let's simply pack as
many iovec[] segments to every fuse-request as possible.

To estimate performance improvement I used slightly modified fusexmp over
tmpfs (clearing O_DIRECT bit from fi->flags in xmp_open). The test opened
a file with O_DIRECT, then called readv/writev in a loop. An iovec[] for
readv/writev consisted of 32 segments of 4K each. The throughput on some
commodity (rather feeble) server was (in MB/sec):

        original / patched
writev: ~107     / ~480
readv:  ~114     / ~569

We're exploring possibility to use fuse for our own distributed storage
implementation and big iovec[] arrays of many page-size chunks is typical
use-case for device virtualization thread performing i/o on behalf of
virtual-machine it serves.

Changed in v2:
 - inline array of page pointers req->pages[] is replaced with dynamically
   allocated one; the number of elements is calculated a bit more
   intelligently than being equal to FUSE_MAX_PAGES_PER_REQ; this is done
   for the sake of memory economy.
 - a dynamically allocated array of so-called 'page descriptors' - an offset
   in page plus the length of fragment - is added to fuse_req; this is done
   to simplify processing fuse requests covering several iov-s.

Changed in v3:
 - used iov_iter in fuse_get_user_pages() and __fuse_direct_io()
 - zeroed req->pages[] array on allocation
 - a bunch of minor cleanup changes:
    - used unsigned for npages
    - freed req->pages[] and req->page_descs[] together
    - renamed fuse_get_ua() to fuse_get_user_addr()
    - renamed fuse_get_fr_sz() to fuse_get_user_size()
    - simplified loop in fuse_page_descs_length_init()
 - rebased on v3.7-rc2

Thanks,
Maxim

---

Maxim Patlasov (12):
      fuse: general infrastructure for pages[] of variable size
      fuse: categorize fuse_get_req()
      fuse: rework fuse_retrieve()
      fuse: rework fuse_readpages()
      fuse: rework fuse_perform_write()
      fuse: rework fuse_do_ioctl()
      fuse: add per-page descriptor <offset, length> to fuse_req
      fuse: use req->page_descs[] for argpages cases
      mm: minor cleanup of iov_iter_single_seg_count()
      fuse: pass iov[] to fuse_get_user_pages()
      fuse: optimize fuse_get_user_pages()
      fuse: optimize __fuse_direct_io()


 fs/fuse/cuse.c     |    3 -
 fs/fuse/dev.c      |   98 +++++++++++++++------
 fs/fuse/dir.c      |   39 ++++----
 fs/fuse/file.c     |  242 ++++++++++++++++++++++++++++++++++------------------
 fs/fuse/fuse_i.h   |   47 ++++++++--
 fs/fuse/inode.c    |    6 +
 include/linux/fs.h |    2 
 mm/filemap.c       |    2 
 8 files changed, 292 insertions(+), 147 deletions(-)

-- 
Signature

[PATCH 01/12] fuse: general infrastructure for pages[] of variable size

[Maxim Patlasov]

The patch removes inline array of FUSE_MAX_PAGES_PER_REQ page pointers from
fuse_req. Instead of that, req->pages may now point either to small inline
array or to an array allocated dynamically.

This essentially means that all callers of fuse_request_alloc[_nofs] should
pass the number of pages needed explicitly.

The patch doesn't make any logic changes.

Signed-off-by: Maxim Patlasov <mpatlasov@parallels.com>
---
 fs/fuse/dev.c    |   47 ++++++++++++++++++++++++++++++++++-------------
 fs/fuse/file.c   |    4 ++--
 fs/fuse/fuse_i.h |   15 ++++++++++++---
 fs/fuse/inode.c  |    4 ++--
 4 files changed, 50 insertions(+), 20 deletions(-)

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index 8c23fa7..54c2d84 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -34,34 +34,55 @@ static struct fuse_conn *fuse_get_conn(struct file *file)
 	return file->private_data;
 }
 
-static void fuse_request_init(struct fuse_req *req)
+static void fuse_request_init(struct fuse_req *req, struct page **pages,
+			      unsigned npages)
 {
 	memset(req, 0, sizeof(*req));
+	memset(pages, 0, sizeof(*pages) * npages);
 	INIT_LIST_HEAD(&req->list);
 	INIT_LIST_HEAD(&req->intr_entry);
 	init_waitqueue_head(&req->waitq);
 	atomic_set(&req->count, 1);
+	req->pages = pages;
+	req->max_pages = npages;
 }
 
-struct fuse_req *fuse_request_alloc(void)
+static struct fuse_req *__fuse_request_alloc(unsigned npages, gfp_t flags)
 {
-	struct fuse_req *req = kmem_cache_alloc(fuse_req_cachep, GFP_KERNEL);
-	if (req)
-		fuse_request_init(req);
+	struct fuse_req *req = kmem_cache_alloc(fuse_req_cachep, flags);
+	if (req) {
+		struct page **pages;
+
+		if (npages <= FUSE_REQ_INLINE_PAGES)
+			pages = req->inline_pages;
+		else
+			pages = kmalloc(sizeof(struct page *) * npages, flags);
+
+		if (!pages) {
+			kmem_cache_free(fuse_req_cachep, req);
+			return NULL;
+		}
+
+		fuse_request_init(req, pages, npages);
+	}
 	return req;
 }
+
+struct fuse_req *fuse_request_alloc(unsigned npages)
+{
+	return __fuse_request_alloc(npages, GFP_KERNEL);
+}
 EXPORT_SYMBOL_GPL(fuse_request_alloc);
 
-struct fuse_req *fuse_request_alloc_nofs(void)
+struct fuse_req *fuse_request_alloc_nofs(unsigned npages)
 {
-	struct fuse_req *req = kmem_cache_alloc(fuse_req_cachep, GFP_NOFS);
-	if (req)
-		fuse_request_init(req);
-	return req;
+	return __fuse_request_alloc(npages, GFP_NOFS);
 }
 
 void fuse_request_free(struct fuse_req *req)
 {
+	if (req->pages != req->inline_pages)
+		kfree(req->pages);
 	kmem_cache_free(fuse_req_cachep, req);
 }
 
@@ -116,7 +137,7 @@ struct fuse_req *fuse_get_req(struct fuse_conn *fc)
 	if (!fc->connected)
 		goto out;
 
-	req = fuse_request_alloc();
+	req = fuse_request_alloc(FUSE_MAX_PAGES_PER_REQ);
 	err = -ENOMEM;
 	if (!req)
 		goto out;
@@ -165,7 +186,7 @@ static void put_reserved_req(struct fuse_conn *fc, struct fuse_req *req)
 	struct fuse_file *ff = file->private_data;
 
 	spin_lock(&fc->lock);
-	fuse_request_init(req);
+	fuse_request_init(req, req->pages, req->max_pages);
 	BUG_ON(ff->reserved_req);
 	ff->reserved_req = req;
 	wake_up_all(&fc->reserved_req_waitq);
@@ -192,7 +213,7 @@ struct fuse_req *fuse_get_req_nofail(struct fuse_conn *fc, struct file *file)
 
 	atomic_inc(&fc->num_waiting);
 	wait_event(fc->blocked_waitq, !fc->blocked);
-	req = fuse_request_alloc();
+	req = fuse_request_alloc(FUSE_MAX_PAGES_PER_REQ);
 	if (!req)
 		req = get_reserved_req(fc, file);
 
diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 78d2837..967e3e6 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -57,7 +57,7 @@ struct fuse_file *fuse_file_alloc(struct fuse_conn *fc)
 		return NULL;
 
 	ff->fc = fc;
-	ff->reserved_req = fuse_request_alloc();
+	ff->reserved_req = fuse_request_alloc(0);
 	if (unlikely(!ff->reserved_req)) {
 		kfree(ff);
 		return NULL;
@@ -1272,7 +1272,7 @@ static int fuse_writepage_locked(struct page *page)
 
 	set_page_writeback(page);
 
-	req = fuse_request_alloc_nofs();
+	req = fuse_request_alloc_nofs(1);
 	if (!req)
 		goto err;
 
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index e24dd74..d52a2fa 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -44,6 +44,9 @@
     doing the mount will be allowed to access the filesystem */
 #define FUSE_ALLOW_OTHER         (1 << 1)
 
+/** Number of page pointers embedded in fuse_req */
+#define FUSE_REQ_INLINE_PAGES 1
+
 /** List of active connections */
 extern struct list_head fuse_conn_list;
 
@@ -291,7 +294,13 @@ struct fuse_req {
 	} misc;
 
 	/** page vector */
-	struct page *pages[FUSE_MAX_PAGES_PER_REQ];
+	struct page **pages;
+
+	/** size of the 'pages' array */
+	unsigned max_pages;
+
+	/** inline page vector */
+	struct page *inline_pages[FUSE_REQ_INLINE_PAGES];
 
 	/** number of pages in vector */
 	unsigned num_pages;
@@ -658,9 +667,9 @@ void fuse_ctl_cleanup(void);
 /**
  * Allocate a request
  */
-struct fuse_req *fuse_request_alloc(void);
+struct fuse_req *fuse_request_alloc(unsigned npages);
 
-struct fuse_req *fuse_request_alloc_nofs(void);
+struct fuse_req *fuse_request_alloc_nofs(unsigned npages);
 
 /**
  * Free a request
diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index f0eda12..0fda955 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -1029,12 +1029,12 @@ static int fuse_fill_super(struct super_block *sb, void *data, int silent)
 	/* only now - we want root dentry with NULL ->d_op */
 	sb->s_d_op = &fuse_dentry_operations;
 
-	init_req = fuse_request_alloc();
+	init_req = fuse_request_alloc(0);
 	if (!init_req)
 		goto err_put_root;
 
 	if (is_bdev) {
-		fc->destroy_req = fuse_request_alloc();
+		fc->destroy_req = fuse_request_alloc(0);
 		if (!fc->destroy_req)
 			goto err_free_init_req;
 	}

[PATCH 02/12] fuse: categorize fuse_get_req()

[Maxim Patlasov]

The patch categorizes all fuse_get_req() invocations into two categories:
 - fuse_get_req_nopages(fc) - when caller doesn't care about req->pages
 - fuse_get_req(fc, n) - when caller need n page pointers (n > 0)

Adding fuse_get_req_nopages() helps to avoid numerous fuse_get_req(fc, 0)
scattered over code. Now it's clear from the first glance when a caller need
fuse_req with page pointers.

The patch doesn't make any logic changes. In multi-page case, it silly
allocates array of FUSE_MAX_PAGES_PER_REQ page pointers. This will be amended
by future patches.

Signed-off-by: Maxim Patlasov <mpatlasov@parallels.com>
---
 fs/fuse/cuse.c   |    2 +-
 fs/fuse/dev.c    |   11 ++++++-----
 fs/fuse/dir.c    |   38 +++++++++++++++++++-------------------
 fs/fuse/file.c   |   30 +++++++++++++++---------------
 fs/fuse/fuse_i.h |   17 ++++++++++++++---
 fs/fuse/inode.c  |    2 +-
 6 files changed, 56 insertions(+), 44 deletions(-)

diff --git a/fs/fuse/cuse.c b/fs/fuse/cuse.c
index ee8d550..901a91a 100644
--- a/fs/fuse/cuse.c
+++ b/fs/fuse/cuse.c
@@ -411,7 +411,7 @@ static int cuse_send_init(struct cuse_conn *cc)
 
 	BUILD_BUG_ON(CUSE_INIT_INFO_MAX > PAGE_SIZE);
 
-	req = fuse_get_req(fc);
+	req = fuse_get_req(fc, 1);
 	if (IS_ERR(req)) {
 		rc = PTR_ERR(req);
 		goto err;
diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index 54c2d84..a5d4440 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -118,7 +118,7 @@ static void fuse_req_init_context(struct fuse_req *req)
 	req->in.h.pid = current->pid;
 }
 
-struct fuse_req *fuse_get_req(struct fuse_conn *fc)
+struct fuse_req *fuse_get_req(struct fuse_conn *fc, unsigned npages)
 {
 	struct fuse_req *req;
 	sigset_t oldset;
@@ -137,7 +137,7 @@ struct fuse_req *fuse_get_req(struct fuse_conn *fc)
 	if (!fc->connected)
 		goto out;
 
-	req = fuse_request_alloc(FUSE_MAX_PAGES_PER_REQ);
+	req = fuse_request_alloc(npages);
 	err = -ENOMEM;
 	if (!req)
 		goto out;
@@ -207,13 +207,14 @@ static void put_reserved_req(struct fuse_conn *fc, struct fuse_req *req)
  * filesystem should not have it's own file open.  If deadlock is
  * intentional, it can still be broken by "aborting" the filesystem.
  */
-struct fuse_req *fuse_get_req_nofail(struct fuse_conn *fc, struct file *file)
+struct fuse_req *fuse_get_req_nofail_nopages(struct fuse_conn *fc,
+					     struct file *file)
 {
 	struct fuse_req *req;
 
 	atomic_inc(&fc->num_waiting);
 	wait_event(fc->blocked_waitq, !fc->blocked);
-	req = fuse_request_alloc(FUSE_MAX_PAGES_PER_REQ);
+	req = fuse_request_alloc(0);
 	if (!req)
 		req = get_reserved_req(fc, file);
 
@@ -1563,7 +1564,7 @@ static int fuse_retrieve(struct fuse_conn *fc, struct inode *inode,
 	unsigned int offset;
 	size_t total_len = 0;
 
-	req = fuse_get_req(fc);
+	req = fuse_get_req(fc, FUSE_MAX_PAGES_PER_REQ);
 	if (IS_ERR(req))
 		return PTR_ERR(req);
 
diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
index 324bc08..1929bfb 100644
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -178,7 +178,7 @@ static int fuse_dentry_revalidate(struct dentry *entry, unsigned int flags)
 			return -ECHILD;
 
 		fc = get_fuse_conn(inode);
-		req = fuse_get_req(fc);
+		req = fuse_get_req_nopages(fc);
 		if (IS_ERR(req))
 			return 0;
 
@@ -271,7 +271,7 @@ int fuse_lookup_name(struct super_block *sb, u64 nodeid, struct qstr *name,
 	if (name->len > FUSE_NAME_MAX)
 		goto out;
 
-	req = fuse_get_req(fc);
+	req = fuse_get_req_nopages(fc);
 	err = PTR_ERR(req);
 	if (IS_ERR(req))
 		goto out;
@@ -391,7 +391,7 @@ static int fuse_create_open(struct inode *dir, struct dentry *entry,
 	if (!forget)
 		goto out_err;
 
-	req = fuse_get_req(fc);
+	req = fuse_get_req_nopages(fc);
 	err = PTR_ERR(req);
 	if (IS_ERR(req))
 		goto out_put_forget_req;
@@ -592,7 +592,7 @@ static int fuse_mknod(struct inode *dir, struct dentry *entry, umode_t mode,
 {
 	struct fuse_mknod_in inarg;
 	struct fuse_conn *fc = get_fuse_conn(dir);
-	struct fuse_req *req = fuse_get_req(fc);
+	struct fuse_req *req = fuse_get_req_nopages(fc);
 	if (IS_ERR(req))
 		return PTR_ERR(req);
 
@@ -623,7 +623,7 @@ static int fuse_mkdir(struct inode *dir, struct dentry *entry, umode_t mode)
 {
 	struct fuse_mkdir_in inarg;
 	struct fuse_conn *fc = get_fuse_conn(dir);
-	struct fuse_req *req = fuse_get_req(fc);
+	struct fuse_req *req = fuse_get_req_nopages(fc);
 	if (IS_ERR(req))
 		return PTR_ERR(req);
 
@@ -647,7 +647,7 @@ static int fuse_symlink(struct inode *dir, struct dentry *entry,
 {
 	struct fuse_conn *fc = get_fuse_conn(dir);
 	unsigned len = strlen(link) + 1;
-	struct fuse_req *req = fuse_get_req(fc);
+	struct fuse_req *req = fuse_get_req_nopages(fc);
 	if (IS_ERR(req))
 		return PTR_ERR(req);
 
@@ -664,7 +664,7 @@ static int fuse_unlink(struct inode *dir, struct dentry *entry)
 {
 	int err;
 	struct fuse_conn *fc = get_fuse_conn(dir);
-	struct fuse_req *req = fuse_get_req(fc);
+	struct fuse_req *req = fuse_get_req_nopages(fc);
 	if (IS_ERR(req))
 		return PTR_ERR(req);
 
@@ -696,7 +696,7 @@ static int fuse_rmdir(struct inode *dir, struct dentry *entry)
 {
 	int err;
 	struct fuse_conn *fc = get_fuse_conn(dir);
-	struct fuse_req *req = fuse_get_req(fc);
+	struct fuse_req *req = fuse_get_req_nopages(fc);
 	if (IS_ERR(req))
 		return PTR_ERR(req);
 
@@ -723,7 +723,7 @@ static int fuse_rename(struct inode *olddir, struct dentry *oldent,
 	int err;
 	struct fuse_rename_in inarg;
 	struct fuse_conn *fc = get_fuse_conn(olddir);
-	struct fuse_req *req = fuse_get_req(fc);
+	struct fuse_req *req = fuse_get_req_nopages(fc);
 
 	if (IS_ERR(req))
 		return PTR_ERR(req);
@@ -776,7 +776,7 @@ static int fuse_link(struct dentry *entry, struct inode *newdir,
 	struct fuse_link_in inarg;
 	struct inode *inode = entry->d_inode;
 	struct fuse_conn *fc = get_fuse_conn(inode);
-	struct fuse_req *req = fuse_get_req(fc);
+	struct fuse_req *req = fuse_get_req_nopages(fc);
 	if (IS_ERR(req))
 		return PTR_ERR(req);
 
@@ -848,7 +848,7 @@ static int fuse_do_getattr(struct inode *inode, struct kstat *stat,
 	struct fuse_req *req;
 	u64 attr_version;
 
-	req = fuse_get_req(fc);
+	req = fuse_get_req_nopages(fc);
 	if (IS_ERR(req))
 		return PTR_ERR(req);
 
@@ -1029,7 +1029,7 @@ static int fuse_access(struct inode *inode, int mask)
 	if (fc->no_access)
 		return 0;
 
-	req = fuse_get_req(fc);
+	req = fuse_get_req_nopages(fc);
 	if (IS_ERR(req))
 		return PTR_ERR(req);
 
@@ -1167,7 +1167,7 @@ static int fuse_readdir(struct file *file, void *dstbuf, filldir_t filldir)
 	if (is_bad_inode(inode))
 		return -EIO;
 
-	req = fuse_get_req(fc);
+	req = fuse_get_req(fc, 1);
 	if (IS_ERR(req))
 		return PTR_ERR(req);
 
@@ -1197,7 +1197,7 @@ static char *read_link(struct dentry *dentry)
 {
 	struct inode *inode = dentry->d_inode;
 	struct fuse_conn *fc = get_fuse_conn(inode);
-	struct fuse_req *req = fuse_get_req(fc);
+	struct fuse_req *req = fuse_get_req_nopages(fc);
 	char *link;
 
 	if (IS_ERR(req))
@@ -1410,7 +1410,7 @@ static int fuse_do_setattr(struct dentry *entry, struct iattr *attr,
 	if (attr->ia_valid & ATTR_SIZE)
 		is_truncate = true;
 
-	req = fuse_get_req(fc);
+	req = fuse_get_req_nopages(fc);
 	if (IS_ERR(req))
 		return PTR_ERR(req);
 
@@ -1518,7 +1518,7 @@ static int fuse_setxattr(struct dentry *entry, const char *name,
 	if (fc->no_setxattr)
 		return -EOPNOTSUPP;
 
-	req = fuse_get_req(fc);
+	req = fuse_get_req_nopages(fc);
 	if (IS_ERR(req))
 		return PTR_ERR(req);
 
@@ -1557,7 +1557,7 @@ static ssize_t fuse_getxattr(struct dentry *entry, const char *name,
 	if (fc->no_getxattr)
 		return -EOPNOTSUPP;
 
-	req = fuse_get_req(fc);
+	req = fuse_get_req_nopages(fc);
 	if (IS_ERR(req))
 		return PTR_ERR(req);
 
@@ -1609,7 +1609,7 @@ static ssize_t fuse_listxattr(struct dentry *entry, char *list, size_t size)
 	if (fc->no_listxattr)
 		return -EOPNOTSUPP;
 
-	req = fuse_get_req(fc);
+	req = fuse_get_req_nopages(fc);
 	if (IS_ERR(req))
 		return PTR_ERR(req);
 
@@ -1654,7 +1654,7 @@ static int fuse_removexattr(struct dentry *entry, const char *name)
 	if (fc->no_removexattr)
 		return -EOPNOTSUPP;
 
-	req = fuse_get_req(fc);
+	req = fuse_get_req_nopages(fc);
 	if (IS_ERR(req))
 		return PTR_ERR(req);
 
diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 967e3e6..ba7447d 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -25,7 +25,7 @@ static int fuse_send_open(struct fuse_conn *fc, u64 nodeid, struct file *file,
 	struct fuse_req *req;
 	int err;
 
-	req = fuse_get_req(fc);
+	req = fuse_get_req_nopages(fc);
 	if (IS_ERR(req))
 		return PTR_ERR(req);
 
@@ -368,7 +368,7 @@ static int fuse_flush(struct file *file, fl_owner_t id)
 	if (fc->no_flush)
 		return 0;
 
-	req = fuse_get_req_nofail(fc, file);
+	req = fuse_get_req_nofail_nopages(fc, file);
 	memset(&inarg, 0, sizeof(inarg));
 	inarg.fh = ff->fh;
 	inarg.lock_owner = fuse_lock_owner_id(fc, id);
@@ -436,7 +436,7 @@ int fuse_fsync_common(struct file *file, loff_t start, loff_t end,
 
 	fuse_sync_writes(inode);
 
-	req = fuse_get_req(fc);
+	req = fuse_get_req_nopages(fc);
 	if (IS_ERR(req)) {
 		err = PTR_ERR(req);
 		goto out;
@@ -544,7 +544,7 @@ static int fuse_readpage(struct file *file, struct page *page)
 	 */
 	fuse_wait_on_page_writeback(inode, page->index);
 
-	req = fuse_get_req(fc);
+	req = fuse_get_req(fc, 1);
 	err = PTR_ERR(req);
 	if (IS_ERR(req))
 		goto out;
@@ -657,7 +657,7 @@ static int fuse_readpages_fill(void *_data, struct page *page)
 	     (req->num_pages + 1) * PAGE_CACHE_SIZE > fc->max_read ||
 	     req->pages[req->num_pages - 1]->index + 1 != page->index)) {
 		fuse_send_readpages(req, data->file);
-		data->req = req = fuse_get_req(fc);
+		data->req = req = fuse_get_req(fc, FUSE_MAX_PAGES_PER_REQ);
 		if (IS_ERR(req)) {
 			unlock_page(page);
 			return PTR_ERR(req);
@@ -683,7 +683,7 @@ static int fuse_readpages(struct file *file, struct address_space *mapping,
 
 	data.file = file;
 	data.inode = inode;
-	data.req = fuse_get_req(fc);
+	data.req = fuse_get_req(fc, FUSE_MAX_PAGES_PER_REQ);
 	err = PTR_ERR(data.req);
 	if (IS_ERR(data.req))
 		goto out;
@@ -890,7 +890,7 @@ static ssize_t fuse_perform_write(struct file *file,
 		struct fuse_req *req;
 		ssize_t count;
 
-		req = fuse_get_req(fc);
+		req = fuse_get_req(fc, FUSE_MAX_PAGES_PER_REQ);
 		if (IS_ERR(req)) {
 			err = PTR_ERR(req);
 			break;
@@ -1072,7 +1072,7 @@ ssize_t fuse_direct_io(struct file *file, const char __user *buf,
 	ssize_t res = 0;
 	struct fuse_req *req;
 
-	req = fuse_get_req(fc);
+	req = fuse_get_req(fc, FUSE_MAX_PAGES_PER_REQ);
 	if (IS_ERR(req))
 		return PTR_ERR(req);
 
@@ -1108,7 +1108,7 @@ ssize_t fuse_direct_io(struct file *file, const char __user *buf,
 			break;
 		if (count) {
 			fuse_put_request(fc, req);
-			req = fuse_get_req(fc);
+			req = fuse_get_req(fc, FUSE_MAX_PAGES_PER_REQ);
 			if (IS_ERR(req))
 				break;
 		}
@@ -1471,7 +1471,7 @@ static int fuse_getlk(struct file *file, struct file_lock *fl)
 	struct fuse_lk_out outarg;
 	int err;
 
-	req = fuse_get_req(fc);
+	req = fuse_get_req_nopages(fc);
 	if (IS_ERR(req))
 		return PTR_ERR(req);
 
@@ -1506,7 +1506,7 @@ static int fuse_setlk(struct file *file, struct file_lock *fl, int flock)
 	if (fl->fl_flags & FL_CLOSE)
 		return 0;
 
-	req = fuse_get_req(fc);
+	req = fuse_get_req_nopages(fc);
 	if (IS_ERR(req))
 		return PTR_ERR(req);
 
@@ -1575,7 +1575,7 @@ static sector_t fuse_bmap(struct address_space *mapping, sector_t block)
 	if (!inode->i_sb->s_bdev || fc->no_bmap)
 		return 0;
 
-	req = fuse_get_req(fc);
+	req = fuse_get_req_nopages(fc);
 	if (IS_ERR(req))
 		return 0;
 
@@ -1873,7 +1873,7 @@ long fuse_do_ioctl(struct file *file, unsigned int cmd, unsigned long arg,
 		num_pages++;
 	}
 
-	req = fuse_get_req(fc);
+	req = fuse_get_req(fc, FUSE_MAX_PAGES_PER_REQ);
 	if (IS_ERR(req)) {
 		err = PTR_ERR(req);
 		req = NULL;
@@ -2076,7 +2076,7 @@ unsigned fuse_file_poll(struct file *file, poll_table *wait)
 		fuse_register_polled_file(fc, ff);
 	}
 
-	req = fuse_get_req(fc);
+	req = fuse_get_req_nopages(fc);
 	if (IS_ERR(req))
 		return POLLERR;
 
@@ -2194,7 +2194,7 @@ long fuse_file_fallocate(struct file *file, int mode, loff_t offset,
 	if (fc->no_fallocate)
 		return -EOPNOTSUPP;
 
-	req = fuse_get_req(fc);
+	req = fuse_get_req_nopages(fc);
 	if (IS_ERR(req))
 		return PTR_ERR(req);
 
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index d52a2fa..641c8f0 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -677,14 +677,25 @@ struct fuse_req *fuse_request_alloc_nofs(unsigned npages);
 void fuse_request_free(struct fuse_req *req);
 
 /**
- * Get a request, may fail with -ENOMEM
+ * Get a request, may fail with -ENOMEM,
+ * caller should specify # elements in req->pages[] explicitly
  */
-struct fuse_req *fuse_get_req(struct fuse_conn *fc);
+struct fuse_req *fuse_get_req(struct fuse_conn *fc, unsigned npages);
+
+/**
+ * Get a request, may fail with -ENOMEM,
+ * useful for callers who doesn't use req->pages[]
+ */
+static inline struct fuse_req *fuse_get_req_nopages(struct fuse_conn *fc)
+{
+	return fuse_get_req(fc, 0);
+}
 
 /**
  * Gets a requests for a file operation, always succeeds
  */
-struct fuse_req *fuse_get_req_nofail(struct fuse_conn *fc, struct file *file);
+struct fuse_req *fuse_get_req_nofail_nopages(struct fuse_conn *fc,
+					     struct file *file);
 
 /**
  * Decrement reference count of a request.  If count goes to zero free
diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index 0fda955..32195fe 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -413,7 +413,7 @@ static int fuse_statfs(struct dentry *dentry, struct kstatfs *buf)
 		return 0;
 	}
 
-	req = fuse_get_req(fc);
+	req = fuse_get_req_nopages(fc);
 	if (IS_ERR(req))
 		return PTR_ERR(req);
 

[PATCH 03/12] fuse: rework fuse_retrieve()

[Maxim Patlasov]

The patch reworks fuse_retrieve() to allocate only so many page pointers
as needed. The core part of the patch is the following calculation:

	num_pages = (num + offset + PAGE_SIZE - 1) >> PAGE_SHIFT;

(thanks Miklos for formula). All other changes are mostly shuffling lines.

Signed-off-by: Maxim Patlasov <mpatlasov@parallels.com>
---
 fs/fuse/dev.c |   25 +++++++++++++++----------
 1 files changed, 15 insertions(+), 10 deletions(-)

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index a5d4440..1266a5c 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -1563,13 +1563,24 @@ static int fuse_retrieve(struct fuse_conn *fc, struct inode *inode,
 	unsigned int num;
 	unsigned int offset;
 	size_t total_len = 0;
+	int num_pages;
 
-	req = fuse_get_req(fc, FUSE_MAX_PAGES_PER_REQ);
+	offset = outarg->offset & ~PAGE_CACHE_MASK;
+	file_size = i_size_read(inode);
+
+	num = outarg->size;
+	if (outarg->offset > file_size)
+		num = 0;
+	else if (outarg->offset + num > file_size)
+		num = file_size - outarg->offset;
+
+	num_pages = (num + offset + PAGE_SIZE - 1) >> PAGE_SHIFT;
+	num_pages = min(num_pages, FUSE_MAX_PAGES_PER_REQ);
+
+	req = fuse_get_req(fc, num_pages);
 	if (IS_ERR(req))
 		return PTR_ERR(req);
 
-	offset = outarg->offset & ~PAGE_CACHE_MASK;
-
 	req->in.h.opcode = FUSE_NOTIFY_REPLY;
 	req->in.h.nodeid = outarg->nodeid;
 	req->in.numargs = 2;
@@ -1578,14 +1589,8 @@ static int fuse_retrieve(struct fuse_conn *fc, struct inode *inode,
 	req->end = fuse_retrieve_end;
 
 	index = outarg->offset >> PAGE_CACHE_SHIFT;
-	file_size = i_size_read(inode);
-	num = outarg->size;
-	if (outarg->offset > file_size)
-		num = 0;
-	else if (outarg->offset + num > file_size)
-		num = file_size - outarg->offset;
 
-	while (num && req->num_pages < FUSE_MAX_PAGES_PER_REQ) {
+	while (num && req->num_pages < num_pages) {
 		struct page *page;
 		unsigned int this_num;
 

[PATCH 04/12] fuse: rework fuse_readpages()

[Maxim Patlasov]

The patch uses 'nr_pages' argument of fuse_readpages() as heuristics for the
number of page pointers to allocate.

This can be improved further by taking in consideration fc->max_read and gaps
between page indices, but it's not clear whether it's worthy or not.

Signed-off-by: Maxim Patlasov <mpatlasov@parallels.com>
---
 fs/fuse/file.c |   16 ++++++++++++++--
 1 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index ba7447d..9872acc 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -641,6 +641,7 @@ struct fuse_fill_data {
 	struct fuse_req *req;
 	struct file *file;
 	struct inode *inode;
+	unsigned nr_pages;
 };
 
 static int fuse_readpages_fill(void *_data, struct page *page)
@@ -656,16 +657,25 @@ static int fuse_readpages_fill(void *_data, struct page *page)
 	    (req->num_pages == FUSE_MAX_PAGES_PER_REQ ||
 	     (req->num_pages + 1) * PAGE_CACHE_SIZE > fc->max_read ||
 	     req->pages[req->num_pages - 1]->index + 1 != page->index)) {
+		int nr_alloc = min_t(unsigned, data->nr_pages,
+				     FUSE_MAX_PAGES_PER_REQ);
 		fuse_send_readpages(req, data->file);
-		data->req = req = fuse_get_req(fc, FUSE_MAX_PAGES_PER_REQ);
+		data->req = req = fuse_get_req(fc, nr_alloc);
 		if (IS_ERR(req)) {
 			unlock_page(page);
 			return PTR_ERR(req);
 		}
 	}
+
+	if (WARN_ON(req->num_pages >= req->max_pages)) {
+		fuse_put_request(fc, req);
+		return -EIO;
+	}
+
 	page_cache_get(page);
 	req->pages[req->num_pages] = page;
 	req->num_pages++;
+	data->nr_pages--;
 	return 0;
 }
 
@@ -676,6 +686,7 @@ static int fuse_readpages(struct file *file, struct address_space *mapping,
 	struct fuse_conn *fc = get_fuse_conn(inode);
 	struct fuse_fill_data data;
 	int err;
+	int nr_alloc = min_t(unsigned, nr_pages, FUSE_MAX_PAGES_PER_REQ);
 
 	err = -EIO;
 	if (is_bad_inode(inode))
@@ -683,7 +694,8 @@ static int fuse_readpages(struct file *file, struct address_space *mapping,
 
 	data.file = file;
 	data.inode = inode;
-	data.req = fuse_get_req(fc, FUSE_MAX_PAGES_PER_REQ);
+	data.req = fuse_get_req(fc, nr_alloc);
+	data.nr_pages = nr_pages;
 	err = PTR_ERR(data.req);
 	if (IS_ERR(data.req))
 		goto out;

[PATCH 05/12] fuse: rework fuse_perform_write()

[Maxim Patlasov]

The patch allocates as many page pointers in fuse_req as needed to cover
interval [pos .. pos+len-1]. Inline helper fuse_wr_pages() is introduced
to hide this cumbersome arithmetic.

Signed-off-by: Maxim Patlasov <mpatlasov@parallels.com>
---
 fs/fuse/file.c |   13 +++++++++++--
 1 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 9872acc..ba505bc 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -881,11 +881,19 @@ static ssize_t fuse_fill_write_pages(struct fuse_req *req,
 		if (!fc->big_writes)
 			break;
 	} while (iov_iter_count(ii) && count < fc->max_write &&
-		 req->num_pages < FUSE_MAX_PAGES_PER_REQ && offset == 0);
+		 req->num_pages < req->max_pages && offset == 0);
 
 	return count > 0 ? count : err;
 }
 
+static inline unsigned fuse_wr_pages(loff_t pos, size_t len)
+{
+	return min_t(unsigned,
+		     ((pos + len - 1) >> PAGE_CACHE_SHIFT) -
+		     (pos >> PAGE_CACHE_SHIFT) + 1,
+		     FUSE_MAX_PAGES_PER_REQ);
+}
+
 static ssize_t fuse_perform_write(struct file *file,
 				  struct address_space *mapping,
 				  struct iov_iter *ii, loff_t pos)
@@ -901,8 +909,9 @@ static ssize_t fuse_perform_write(struct file *file,
 	do {
 		struct fuse_req *req;
 		ssize_t count;
+		unsigned nr_pages = fuse_wr_pages(pos, iov_iter_count(ii));
 
-		req = fuse_get_req(fc, FUSE_MAX_PAGES_PER_REQ);
+		req = fuse_get_req(fc, nr_pages);
 		if (IS_ERR(req)) {
 			err = PTR_ERR(req);
 			break;

[PATCH 06/12] fuse: rework fuse_do_ioctl()

[Maxim Patlasov]

fuse_do_ioctl() already calculates the number of pages it's going to use. It is
stored in 'num_pages' variable. So the patch simply uses it for allocating
fuse_req.

Signed-off-by: Maxim Patlasov <mpatlasov@parallels.com>
---
 fs/fuse/file.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index ba505bc..d5d23de 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -1894,7 +1894,7 @@ long fuse_do_ioctl(struct file *file, unsigned int cmd, unsigned long arg,
 		num_pages++;
 	}
 
-	req = fuse_get_req(fc, FUSE_MAX_PAGES_PER_REQ);
+	req = fuse_get_req(fc, num_pages);
 	if (IS_ERR(req)) {
 		err = PTR_ERR(req);
 		req = NULL;

[PATCH 07/12] fuse: add per-page descriptor <offset, length> to fuse_req

[Maxim Patlasov]

The ability to save page pointers along with lengths and offsets in fuse_req
will be useful to cover several iovec-s with a single fuse_req.

Per-request page_offset is removed because anybody who need it can use
req->page_descs[0].offset instead.

Signed-off-by: Maxim Patlasov <mpatlasov@parallels.com>
---
 fs/fuse/dev.c    |   28 ++++++++++++++++++++--------
 fs/fuse/file.c   |   10 +++++-----
 fs/fuse/fuse_i.h |   15 ++++++++++++---
 3 files changed, 37 insertions(+), 16 deletions(-)

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index 1266a5c..5530fb3 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -35,15 +35,18 @@ static struct fuse_conn *fuse_get_conn(struct file *file)
 }
 
 static void fuse_request_init(struct fuse_req *req, struct page **pages,
+			      struct fuse_page_desc *page_descs,
 			      unsigned npages)
 {
 	memset(req, 0, sizeof(*req));
 	memset(pages, 0, sizeof(*pages) * npages);
+	memset(page_descs, 0, sizeof(*page_descs) * npages);
 	INIT_LIST_HEAD(&req->list);
 	INIT_LIST_HEAD(&req->intr_entry);
 	init_waitqueue_head(&req->waitq);
 	atomic_set(&req->count, 1);
 	req->pages = pages;
+	req->page_descs = page_descs;
 	req->max_pages = npages;
 }
 
@@ -52,18 +55,25 @@ static struct fuse_req *__fuse_request_alloc(unsigned npages, gfp_t flags)
 	struct fuse_req *req = kmem_cache_alloc(fuse_req_cachep, flags);
 	if (req) {
 		struct page **pages;
+		struct fuse_page_desc *page_descs;
 
-		if (npages <= FUSE_REQ_INLINE_PAGES)
+		if (npages <= FUSE_REQ_INLINE_PAGES) {
 			pages = req->inline_pages;
-		else
+			page_descs = req->inline_page_descs;
+		} else {
 			pages = kmalloc(sizeof(struct page *) * npages, flags);
+			page_descs = kmalloc(sizeof(struct fuse_page_desc) *
+					     npages, flags);
+		}
 
-		if (!pages) {
+		if (!pages || !page_descs) {
+			kfree(pages);
+			kfree(page_descs);
 			kmem_cache_free(fuse_req_cachep, req);
 			return NULL;
 		}
 
-		fuse_request_init(req, pages, npages);
+		fuse_request_init(req, pages, page_descs, npages);
 	}
 	return req;
 }
@@ -81,8 +91,10 @@ struct fuse_req *fuse_request_alloc_nofs(unsigned npages)
 
 void fuse_request_free(struct fuse_req *req)
 {
-	if (req->pages != req->inline_pages)
+	if (req->pages != req->inline_pages) {
 		kfree(req->pages);
+		kfree(req->page_descs);
+	}
 	kmem_cache_free(fuse_req_cachep, req);
 }
 
@@ -186,7 +198,7 @@ static void put_reserved_req(struct fuse_conn *fc, struct fuse_req *req)
 	struct fuse_file *ff = file->private_data;
 
 	spin_lock(&fc->lock);
-	fuse_request_init(req, req->pages, req->max_pages);
+	fuse_request_init(req, req->pages, req->page_descs, req->max_pages);
 	BUG_ON(ff->reserved_req);
 	ff->reserved_req = req;
 	wake_up_all(&fc->reserved_req_waitq);
@@ -877,7 +889,7 @@ static int fuse_copy_pages(struct fuse_copy_state *cs, unsigned nbytes,
 {
 	unsigned i;
 	struct fuse_req *req = cs->req;
-	unsigned offset = req->page_offset;
+	unsigned offset = req->page_descs[0].offset;
 	unsigned count = min(nbytes, (unsigned) PAGE_SIZE - offset);
 
 	for (i = 0; i < req->num_pages && (nbytes || zeroing); i++) {
@@ -1585,7 +1597,7 @@ static int fuse_retrieve(struct fuse_conn *fc, struct inode *inode,
 	req->in.h.nodeid = outarg->nodeid;
 	req->in.numargs = 2;
 	req->in.argpages = 1;
-	req->page_offset = offset;
+	req->page_descs[0].offset = offset;
 	req->end = fuse_retrieve_end;
 
 	index = outarg->offset >> PAGE_CACHE_SHIFT;
diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index d5d23de..c95ecb5 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -798,7 +798,7 @@ static size_t fuse_send_write_pages(struct fuse_req *req, struct file *file,
 
 	res = fuse_send_write(req, file, pos, count, NULL);
 
-	offset = req->page_offset;
+	offset = req->page_descs[0].offset;
 	count = res;
 	for (i = 0; i < req->num_pages; i++) {
 		struct page *page = req->pages[i];
@@ -829,7 +829,7 @@ static ssize_t fuse_fill_write_pages(struct fuse_req *req,
 	int err;
 
 	req->in.argpages = 1;
-	req->page_offset = offset;
+	req->page_descs[0].offset = offset;
 
 	do {
 		size_t tmp;
@@ -1070,14 +1070,14 @@ static int fuse_get_user_pages(struct fuse_req *req, const char __user *buf,
 		return npages;
 
 	req->num_pages = npages;
-	req->page_offset = offset;
+	req->page_descs[0].offset = offset;
 
 	if (write)
 		req->in.argpages = 1;
 	else
 		req->out.argpages = 1;
 
-	nbytes = (req->num_pages << PAGE_SHIFT) - req->page_offset;
+	nbytes = (req->num_pages << PAGE_SHIFT) - req->page_descs[0].offset;
 	*nbytesp = min(*nbytesp, nbytes);
 
 	return 0;
@@ -1314,7 +1314,7 @@ static int fuse_writepage_locked(struct page *page)
 	req->in.argpages = 1;
 	req->num_pages = 1;
 	req->pages[0] = tmp_page;
-	req->page_offset = 0;
+	req->page_descs[0].offset = 0;
 	req->end = fuse_writepage_end;
 	req->inode = inode;
 
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index 641c8f0..ee7970307f 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -203,6 +203,12 @@ struct fuse_out {
 	struct fuse_arg args[3];
 };
 
+/** FUSE page descriptor */
+struct fuse_page_desc {
+	unsigned int length;
+	unsigned int offset;
+};
+
 /** The request state */
 enum fuse_req_state {
 	FUSE_REQ_INIT = 0,
@@ -296,18 +302,21 @@ struct fuse_req {
 	/** page vector */
 	struct page **pages;
 
+	/** page-descriptor vector */
+	struct fuse_page_desc *page_descs;
+
 	/** size of the 'pages' array */
 	unsigned max_pages;
 
 	/** inline page vector */
 	struct page *inline_pages[FUSE_REQ_INLINE_PAGES];
 
+	/** inline page-descriptor vector */
+	struct fuse_page_desc inline_page_descs[FUSE_REQ_INLINE_PAGES];
+
 	/** number of pages in vector */
 	unsigned num_pages;
 
-	/** offset of data on first page */
-	unsigned page_offset;
-
 	/** File used in the request (or NULL) */
 	struct fuse_file *ff;
 

[PATCH 08/12] fuse: use req->page_descs[] for argpages cases

[Maxim Patlasov]

Previously, anyone who set flag 'argpages' only filled req->pages[] and set
per-request page_offset. This patch re-works all cases where argpages=1 to
fill req->page_descs[] properly.

Having req->page_descs[] filled properly allows to re-work fuse_copy_pages()
to copy page fragments described by req->page_descs[]. This will be useful
for next patches optimizing direct_IO.

Signed-off-by: Maxim Patlasov <mpatlasov@parallels.com>
---
 fs/fuse/cuse.c |    1 +
 fs/fuse/dev.c  |    7 +++----
 fs/fuse/dir.c  |    1 +
 fs/fuse/file.c |   20 ++++++++++++++++++++
 4 files changed, 25 insertions(+), 4 deletions(-)

diff --git a/fs/fuse/cuse.c b/fs/fuse/cuse.c
index 901a91a..a2001f0 100644
--- a/fs/fuse/cuse.c
+++ b/fs/fuse/cuse.c
@@ -441,6 +441,7 @@ static int cuse_send_init(struct cuse_conn *cc)
 	req->out.argvar = 1;
 	req->out.argpages = 1;
 	req->pages[0] = page;
+	req->page_descs[0].length = req->out.args[1].size;
 	req->num_pages = 1;
 	req->end = cuse_process_init_reply;
 	fuse_request_send_background(fc, req);
diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index 5530fb3..ece7fcf 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -889,11 +889,11 @@ static int fuse_copy_pages(struct fuse_copy_state *cs, unsigned nbytes,
 {
 	unsigned i;
 	struct fuse_req *req = cs->req;
-	unsigned offset = req->page_descs[0].offset;
-	unsigned count = min(nbytes, (unsigned) PAGE_SIZE - offset);
 
 	for (i = 0; i < req->num_pages && (nbytes || zeroing); i++) {
 		int err;
+		unsigned offset = req->page_descs[i].offset;
+		unsigned count = min(nbytes, req->page_descs[i].length);
 
 		err = fuse_copy_page(cs, &req->pages[i], offset, count,
 				     zeroing);
@@ -901,8 +901,6 @@ static int fuse_copy_pages(struct fuse_copy_state *cs, unsigned nbytes,
 			return err;
 
 		nbytes -= count;
-		count = min(nbytes, (unsigned) PAGE_SIZE);
-		offset = 0;
 	}
 	return 0;
 }
@@ -1612,6 +1610,7 @@ static int fuse_retrieve(struct fuse_conn *fc, struct inode *inode,
 
 		this_num = min_t(unsigned, num, PAGE_CACHE_SIZE - offset);
 		req->pages[req->num_pages] = page;
+		req->page_descs[req->num_pages].length = this_num;
 		req->num_pages++;
 
 		offset = 0;
diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
index 1929bfb..95e4016 100644
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -1179,6 +1179,7 @@ static int fuse_readdir(struct file *file, void *dstbuf, filldir_t filldir)
 	req->out.argpages = 1;
 	req->num_pages = 1;
 	req->pages[0] = page;
+	req->page_descs[0].length = PAGE_SIZE;
 	fuse_read_fill(req, file, file->f_pos, PAGE_SIZE, FUSE_READDIR);
 	fuse_request_send(fc, req);
 	nbytes = req->out.args[0].size;
diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index c95ecb5..51996af 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -555,6 +555,7 @@ static int fuse_readpage(struct file *file, struct page *page)
 	req->out.argpages = 1;
 	req->num_pages = 1;
 	req->pages[0] = page;
+	req->page_descs[0].length = count;
 	num_read = fuse_send_read(req, file, pos, count, NULL);
 	err = req->out.h.error;
 	fuse_put_request(fc, req);
@@ -674,6 +675,7 @@ static int fuse_readpages_fill(void *_data, struct page *page)
 
 	page_cache_get(page);
 	req->pages[req->num_pages] = page;
+	req->page_descs[req->num_pages].length = PAGE_SIZE;
 	req->num_pages++;
 	data->nr_pages--;
 	return 0;
@@ -869,6 +871,7 @@ static ssize_t fuse_fill_write_pages(struct fuse_req *req,
 
 		err = 0;
 		req->pages[req->num_pages] = page;
+		req->page_descs[req->num_pages].length = tmp;
 		req->num_pages++;
 
 		iov_iter_advance(ii, tmp);
@@ -1044,6 +1047,15 @@ static void fuse_release_user_pages(struct fuse_req *req, int write)
 	}
 }
 
+static inline void fuse_page_descs_length_init(struct fuse_req *req)
+{
+	int i;
+
+	for (i = 0; i < req->num_pages; i++)
+		req->page_descs[i].length = PAGE_SIZE -
+			req->page_descs[i].offset;
+}
+
 static int fuse_get_user_pages(struct fuse_req *req, const char __user *buf,
 			       size_t *nbytesp, int write)
 {
@@ -1071,6 +1083,7 @@ static int fuse_get_user_pages(struct fuse_req *req, const char __user *buf,
 
 	req->num_pages = npages;
 	req->page_descs[0].offset = offset;
+	fuse_page_descs_length_init(req);
 
 	if (write)
 		req->in.argpages = 1;
@@ -1078,6 +1091,11 @@ static int fuse_get_user_pages(struct fuse_req *req, const char __user *buf,
 		req->out.argpages = 1;
 
 	nbytes = (req->num_pages << PAGE_SHIFT) - req->page_descs[0].offset;
+
+	if (*nbytesp < nbytes)
+		req->page_descs[req->num_pages - 1].length -=
+			nbytes - *nbytesp;
+
 	*nbytesp = min(*nbytesp, nbytes);
 
 	return 0;
@@ -1315,6 +1333,7 @@ static int fuse_writepage_locked(struct page *page)
 	req->num_pages = 1;
 	req->pages[0] = tmp_page;
 	req->page_descs[0].offset = 0;
+	req->page_descs[0].length = PAGE_SIZE;
 	req->end = fuse_writepage_end;
 	req->inode = inode;
 
@@ -1902,6 +1921,7 @@ long fuse_do_ioctl(struct file *file, unsigned int cmd, unsigned long arg,
 	}
 	memcpy(req->pages, pages, sizeof(req->pages[0]) * num_pages);
 	req->num_pages = num_pages;
+	fuse_page_descs_length_init(req);
 
 	/* okay, let's send it to the client */
 	req->in.h.opcode = FUSE_IOCTL;

[PATCH 09/12] mm: minor cleanup of iov_iter_single_seg_count()

[Maxim Patlasov]

The function does not modify iov_iter which 'i' points to.

Signed-off-by: Maxim Patlasov <mpatlasov@parallels.com>
---
 include/linux/fs.h |    2 +-
 mm/filemap.c       |    2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index b33cfc9..8967baa 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -300,7 +300,7 @@ size_t iov_iter_copy_from_user(struct page *page,
 		struct iov_iter *i, unsigned long offset, size_t bytes);
 void iov_iter_advance(struct iov_iter *i, size_t bytes);
 int iov_iter_fault_in_readable(struct iov_iter *i, size_t bytes);
-size_t iov_iter_single_seg_count(struct iov_iter *i);
+size_t iov_iter_single_seg_count(const struct iov_iter *i);
 
 static inline void iov_iter_init(struct iov_iter *i,
 			const struct iovec *iov, unsigned long nr_segs,
diff --git a/mm/filemap.c b/mm/filemap.c
index 83efee7..24a7ea5 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2056,7 +2056,7 @@ EXPORT_SYMBOL(iov_iter_fault_in_readable);
 /*
  * Return the count of just the current iov_iter segment.
  */
-size_t iov_iter_single_seg_count(struct iov_iter *i)
+size_t iov_iter_single_seg_count(const struct iov_iter *i)
 {
 	const struct iovec *iov = i->iov;
 	if (i->nr_segs == 1)

[PATCH 10/12] fuse: pass iov[] to fuse_get_user_pages()

[Maxim Patlasov]

The patch makes preliminary work for the next patch optimizing scatter-gather
direct IO. The idea is to allow fuse_get_user_pages() to pack as many iov-s
to each fuse request as possible. So, here we only rework all related
call-paths to carry iov[] from fuse_direct_IO() to fuse_get_user_pages().

Signed-off-by: Maxim Patlasov <mpatlasov@parallels.com>
---
 fs/fuse/file.c |  103 +++++++++++++++++++++++++++-----------------------------
 1 files changed, 49 insertions(+), 54 deletions(-)

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 51996af..9934321 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -1056,14 +1056,18 @@ static inline void fuse_page_descs_length_init(struct fuse_req *req)
 			req->page_descs[i].offset;
 }
 
-static int fuse_get_user_pages(struct fuse_req *req, const char __user *buf,
+static int fuse_get_user_pages(struct fuse_req *req, struct iov_iter *ii,
 			       size_t *nbytesp, int write)
 {
 	size_t nbytes = *nbytesp;
-	unsigned long user_addr = (unsigned long) buf;
-	unsigned offset = user_addr & ~PAGE_MASK;
+	size_t frag_size = min(iov_iter_single_seg_count(ii), nbytes);
+	unsigned long user_addr;
+	unsigned offset;
 	int npages;
 
+	user_addr = (unsigned long)ii->iov->iov_base + ii->iov_offset;
+	offset = user_addr & ~PAGE_MASK;
+
 	/* Special case for kernel I/O: can copy directly into the buffer */
 	if (segment_eq(get_fs(), KERNEL_DS)) {
 		if (write)
@@ -1071,10 +1075,12 @@ static int fuse_get_user_pages(struct fuse_req *req, const char __user *buf,
 		else
 			req->out.args[0].value = (void *) user_addr;
 
+		iov_iter_advance(ii, frag_size);
+		*nbytesp = frag_size;
 		return 0;
 	}
 
-	nbytes = min_t(size_t, nbytes, FUSE_MAX_PAGES_PER_REQ << PAGE_SHIFT);
+	nbytes = min_t(size_t, frag_size, FUSE_MAX_PAGES_PER_REQ << PAGE_SHIFT);
 	npages = (nbytes + offset + PAGE_SIZE - 1) >> PAGE_SHIFT;
 	npages = clamp(npages, 1, FUSE_MAX_PAGES_PER_REQ);
 	npages = get_user_pages_fast(user_addr, npages, !write, req->pages);
@@ -1092,17 +1098,19 @@ static int fuse_get_user_pages(struct fuse_req *req, const char __user *buf,
 
 	nbytes = (req->num_pages << PAGE_SHIFT) - req->page_descs[0].offset;
 
-	if (*nbytesp < nbytes)
+	if (frag_size < nbytes)
 		req->page_descs[req->num_pages - 1].length -=
-			nbytes - *nbytesp;
+			nbytes - frag_size;
 
-	*nbytesp = min(*nbytesp, nbytes);
+	*nbytesp = min(frag_size, nbytes);
+	iov_iter_advance(ii, *nbytesp);
 
 	return 0;
 }
 
-ssize_t fuse_direct_io(struct file *file, const char __user *buf,
-		       size_t count, loff_t *ppos, int write)
+static ssize_t __fuse_direct_io(struct file *file, const struct iovec *iov,
+				unsigned long nr_segs, size_t count,
+				loff_t *ppos, int write)
 {
 	struct fuse_file *ff = file->private_data;
 	struct fuse_conn *fc = ff->fc;
@@ -1110,6 +1118,9 @@ ssize_t fuse_direct_io(struct file *file, const char __user *buf,
 	loff_t pos = *ppos;
 	ssize_t res = 0;
 	struct fuse_req *req;
+	struct iov_iter ii;
+
+	iov_iter_init(&ii, iov, nr_segs, count, 0);
 
 	req = fuse_get_req(fc, FUSE_MAX_PAGES_PER_REQ);
 	if (IS_ERR(req))
@@ -1119,7 +1130,7 @@ ssize_t fuse_direct_io(struct file *file, const char __user *buf,
 		size_t nres;
 		fl_owner_t owner = current->files;
 		size_t nbytes = min(count, nmax);
-		int err = fuse_get_user_pages(req, buf, &nbytes, write);
+		int err = fuse_get_user_pages(req, &ii, &nbytes, write);
 		if (err) {
 			res = err;
 			break;
@@ -1142,7 +1153,6 @@ ssize_t fuse_direct_io(struct file *file, const char __user *buf,
 		count -= nres;
 		res += nres;
 		pos += nres;
-		buf += nres;
 		if (nres != nbytes)
 			break;
 		if (count) {
@@ -1159,10 +1169,17 @@ ssize_t fuse_direct_io(struct file *file, const char __user *buf,
 
 	return res;
 }
+
+ssize_t fuse_direct_io(struct file *file, const char __user *buf,
+		       size_t count, loff_t *ppos, int write)
+{
+	struct iovec iov = { .iov_base = (void *)buf, .iov_len = count };
+	return __fuse_direct_io(file, &iov, 1, count, ppos, write);
+}
 EXPORT_SYMBOL_GPL(fuse_direct_io);
 
-static ssize_t fuse_direct_read(struct file *file, char __user *buf,
-				     size_t count, loff_t *ppos)
+static ssize_t __fuse_direct_read(struct file *file, const struct iovec *iov,
+				  unsigned long nr_segs, loff_t *ppos)
 {
 	ssize_t res;
 	struct inode *inode = file->f_path.dentry->d_inode;
@@ -1170,22 +1187,31 @@ static ssize_t fuse_direct_read(struct file *file, char __user *buf,
 	if (is_bad_inode(inode))
 		return -EIO;
 
-	res = fuse_direct_io(file, buf, count, ppos, 0);
+	res = __fuse_direct_io(file, iov, nr_segs, iov_length(iov, nr_segs),
+			       ppos, 0);
 
 	fuse_invalidate_attr(inode);
 
 	return res;
 }
 
-static ssize_t __fuse_direct_write(struct file *file, const char __user *buf,
-				   size_t count, loff_t *ppos)
+static ssize_t fuse_direct_read(struct file *file, char __user *buf,
+				     size_t count, loff_t *ppos)
+{
+	struct iovec iov = { .iov_base = (void *)buf, .iov_len = count };
+	return __fuse_direct_read(file, &iov, 1, ppos);
+}
+
+static ssize_t __fuse_direct_write(struct file *file, const struct iovec *iov,
+				   unsigned long nr_segs, loff_t *ppos)
 {
 	struct inode *inode = file->f_path.dentry->d_inode;
+	size_t count = iov_length(iov, nr_segs);
 	ssize_t res;
 
 	res = generic_write_checks(file, ppos, &count, 0);
 	if (!res) {
-		res = fuse_direct_io(file, buf, count, ppos, 1);
+		res = __fuse_direct_io(file, iov, nr_segs, count, ppos, 1);
 		if (res > 0)
 			fuse_write_update_size(inode, *ppos);
 	}
@@ -1198,6 +1224,7 @@ static ssize_t __fuse_direct_write(struct file *file, const char __user *buf,
 static ssize_t fuse_direct_write(struct file *file, const char __user *buf,
 				 size_t count, loff_t *ppos)
 {
+	struct iovec iov = { .iov_base = (void *)buf, .iov_len = count };
 	struct inode *inode = file->f_path.dentry->d_inode;
 	ssize_t res;
 
@@ -1206,7 +1233,7 @@ static ssize_t fuse_direct_write(struct file *file, const char __user *buf,
 
 	/* Don't allow parallel writes to the same file */
 	mutex_lock(&inode->i_mutex);
-	res = __fuse_direct_write(file, buf, count, ppos);
+	res = __fuse_direct_write(file, &iov, 1, ppos);
 	mutex_unlock(&inode->i_mutex);
 
 	return res;
@@ -2167,41 +2194,6 @@ int fuse_notify_poll_wakeup(struct fuse_conn *fc,
 	return 0;
 }
 
-static ssize_t fuse_loop_dio(struct file *filp, const struct iovec *iov,
-			     unsigned long nr_segs, loff_t *ppos, int rw)
-{
-	const struct iovec *vector = iov;
-	ssize_t ret = 0;
-
-	while (nr_segs > 0) {
-		void __user *base;
-		size_t len;
-		ssize_t nr;
-
-		base = vector->iov_base;
-		len = vector->iov_len;
-		vector++;
-		nr_segs--;
-
-		if (rw == WRITE)
-			nr = __fuse_direct_write(filp, base, len, ppos);
-		else
-			nr = fuse_direct_read(filp, base, len, ppos);
-
-		if (nr < 0) {
-			if (!ret)
-				ret = nr;
-			break;
-		}
-		ret += nr;
-		if (nr != len)
-			break;
-	}
-
-	return ret;
-}
-
-
 static ssize_t
 fuse_direct_IO(int rw, struct kiocb *iocb, const struct iovec *iov,
 			loff_t offset, unsigned long nr_segs)
@@ -2213,7 +2205,10 @@ fuse_direct_IO(int rw, struct kiocb *iocb, const struct iovec *iov,
 	file = iocb->ki_filp;
 	pos = offset;
 
-	ret = fuse_loop_dio(file, iov, nr_segs, &pos, rw);
+	if (rw == WRITE)
+		ret = __fuse_direct_write(file, iov, nr_segs, &pos);
+	else
+		ret = __fuse_direct_read(file, iov, nr_segs, &pos);
 
 	return ret;
 }

[PATCH 11/12] fuse: optimize fuse_get_user_pages()

[Maxim Patlasov]

Let fuse_get_user_pages() pack as many iov-s to a single fuse_req as
possible. This is very beneficial in case of iov[] consisting of many
iov-s of relatively small sizes (e.g. PAGE_SIZE).

Signed-off-by: Maxim Patlasov <mpatlasov@parallels.com>
---
 fs/fuse/file.c |   79 ++++++++++++++++++++++++++++++++++++--------------------
 1 files changed, 51 insertions(+), 28 deletions(-)

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 9934321..fad8c7b 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -1047,29 +1047,37 @@ static void fuse_release_user_pages(struct fuse_req *req, int write)
 	}
 }
 
-static inline void fuse_page_descs_length_init(struct fuse_req *req)
+static inline void fuse_page_descs_length_init(struct fuse_req *req,
+		unsigned index, unsigned nr_pages)
 {
 	int i;
 
-	for (i = 0; i < req->num_pages; i++)
+	for (i = index; i < index + nr_pages; i++)
 		req->page_descs[i].length = PAGE_SIZE -
 			req->page_descs[i].offset;
 }
 
+static inline unsigned long fuse_get_user_addr(const struct iov_iter *ii)
+{
+	return (unsigned long)ii->iov->iov_base + ii->iov_offset;
+}
+
+static inline size_t fuse_get_frag_size(const struct iov_iter *ii,
+					size_t max_size)
+{
+	return min(iov_iter_single_seg_count(ii), max_size);
+}
+
 static int fuse_get_user_pages(struct fuse_req *req, struct iov_iter *ii,
 			       size_t *nbytesp, int write)
 {
-	size_t nbytes = *nbytesp;
-	size_t frag_size = min(iov_iter_single_seg_count(ii), nbytes);
-	unsigned long user_addr;
-	unsigned offset;
-	int npages;
-
-	user_addr = (unsigned long)ii->iov->iov_base + ii->iov_offset;
-	offset = user_addr & ~PAGE_MASK;
+	size_t nbytes = 0;  /* # bytes already packed in req */
 
 	/* Special case for kernel I/O: can copy directly into the buffer */
 	if (segment_eq(get_fs(), KERNEL_DS)) {
+		unsigned long user_addr = fuse_get_user_addr(ii);
+		size_t frag_size = fuse_get_frag_size(ii, *nbytesp);
+
 		if (write)
 			req->in.args[1].value = (void *) user_addr;
 		else
@@ -1080,30 +1088,45 @@ static int fuse_get_user_pages(struct fuse_req *req, struct iov_iter *ii,
 		return 0;
 	}
 
-	nbytes = min_t(size_t, frag_size, FUSE_MAX_PAGES_PER_REQ << PAGE_SHIFT);
-	npages = (nbytes + offset + PAGE_SIZE - 1) >> PAGE_SHIFT;
-	npages = clamp(npages, 1, FUSE_MAX_PAGES_PER_REQ);
-	npages = get_user_pages_fast(user_addr, npages, !write, req->pages);
-	if (npages < 0)
-		return npages;
+	while (nbytes < *nbytesp && req->num_pages < FUSE_MAX_PAGES_PER_REQ) {
+		unsigned npages;
+		unsigned long user_addr = fuse_get_user_addr(ii);
+		unsigned offset = user_addr & ~PAGE_MASK;
+		size_t frag_size = fuse_get_frag_size(ii, *nbytesp - nbytes);
+		int ret;
 
-	req->num_pages = npages;
-	req->page_descs[0].offset = offset;
-	fuse_page_descs_length_init(req);
+		unsigned n = FUSE_MAX_PAGES_PER_REQ - req->num_pages;
+		frag_size = min_t(size_t, frag_size, n << PAGE_SHIFT);
+
+		npages = (frag_size + offset + PAGE_SIZE - 1) >> PAGE_SHIFT;
+		npages = clamp(npages, 1U, n);
+
+		ret = get_user_pages_fast(user_addr, npages, !write,
+					  &req->pages[req->num_pages]);
+		if (ret < 0)
+			return ret;
+
+		npages = ret;
+		frag_size = min_t(size_t, frag_size,
+				  (npages << PAGE_SHIFT) - offset);
+		iov_iter_advance(ii, frag_size);
+
+		req->page_descs[req->num_pages].offset = offset;
+		fuse_page_descs_length_init(req, req->num_pages, npages);
+
+		req->num_pages += npages;
+		req->page_descs[req->num_pages - 1].length -=
+			(npages << PAGE_SHIFT) - offset - frag_size;
+
+		nbytes += frag_size;
+	}
 
 	if (write)
 		req->in.argpages = 1;
 	else
 		req->out.argpages = 1;
 
-	nbytes = (req->num_pages << PAGE_SHIFT) - req->page_descs[0].offset;
-
-	if (frag_size < nbytes)
-		req->page_descs[req->num_pages - 1].length -=
-			nbytes - frag_size;
-
-	*nbytesp = min(frag_size, nbytes);
-	iov_iter_advance(ii, *nbytesp);
+	*nbytesp = nbytes;
 
 	return 0;
 }
@@ -1948,7 +1971,7 @@ long fuse_do_ioctl(struct file *file, unsigned int cmd, unsigned long arg,
 	}
 	memcpy(req->pages, pages, sizeof(req->pages[0]) * num_pages);
 	req->num_pages = num_pages;
-	fuse_page_descs_length_init(req);
+	fuse_page_descs_length_init(req, 0, req->num_pages);
 
 	/* okay, let's send it to the client */
 	req->in.h.opcode = FUSE_IOCTL;

[PATCH 12/12] fuse: optimize __fuse_direct_io()

[Maxim Patlasov]

__fuse_direct_io() allocates fuse-requests by calling fuse_get_req(fc, n). The
patch calculates 'n' based on iov[] array. This is useful because allocating
FUSE_MAX_PAGES_PER_REQ page pointers and descriptors for each fuse request
would be waste of memory in case of iov-s of smaller size.

Signed-off-by: Maxim Patlasov <mpatlasov@parallels.com>
---
 fs/fuse/file.c |   25 +++++++++++++++++++++----
 1 files changed, 21 insertions(+), 4 deletions(-)

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index fad8c7b..1a9ae5a 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -1088,14 +1088,14 @@ static int fuse_get_user_pages(struct fuse_req *req, struct iov_iter *ii,
 		return 0;
 	}
 
-	while (nbytes < *nbytesp && req->num_pages < FUSE_MAX_PAGES_PER_REQ) {
+	while (nbytes < *nbytesp && req->num_pages < req->max_pages) {
 		unsigned npages;
 		unsigned long user_addr = fuse_get_user_addr(ii);
 		unsigned offset = user_addr & ~PAGE_MASK;
 		size_t frag_size = fuse_get_frag_size(ii, *nbytesp - nbytes);
 		int ret;
 
-		unsigned n = FUSE_MAX_PAGES_PER_REQ - req->num_pages;
+		unsigned n = req->max_pages - req->num_pages;
 		frag_size = min_t(size_t, frag_size, n << PAGE_SHIFT);
 
 		npages = (frag_size + offset + PAGE_SIZE - 1) >> PAGE_SHIFT;
@@ -1131,6 +1131,23 @@ static int fuse_get_user_pages(struct fuse_req *req, struct iov_iter *ii,
 	return 0;
 }
 
+static inline int fuse_iter_npages(const struct iov_iter *ii_p)
+{
+	struct iov_iter ii = *ii_p;
+	int npages = 0;
+
+	while (iov_iter_count(&ii) && npages < FUSE_MAX_PAGES_PER_REQ) {
+		unsigned long user_addr = fuse_get_user_addr(&ii);
+		unsigned offset = user_addr & ~PAGE_MASK;
+		size_t frag_size = iov_iter_single_seg_count(&ii);
+
+		npages += (frag_size + offset + PAGE_SIZE - 1) >> PAGE_SHIFT;
+		iov_iter_advance(&ii, frag_size);
+	}
+
+	return min(npages, FUSE_MAX_PAGES_PER_REQ);
+}
+
 static ssize_t __fuse_direct_io(struct file *file, const struct iovec *iov,
 				unsigned long nr_segs, size_t count,
 				loff_t *ppos, int write)
@@ -1145,7 +1162,7 @@ static ssize_t __fuse_direct_io(struct file *file, const struct iovec *iov,
 
 	iov_iter_init(&ii, iov, nr_segs, count, 0);
 
-	req = fuse_get_req(fc, FUSE_MAX_PAGES_PER_REQ);
+	req = fuse_get_req(fc, fuse_iter_npages(&ii));
 	if (IS_ERR(req))
 		return PTR_ERR(req);
 
@@ -1180,7 +1197,7 @@ static ssize_t __fuse_direct_io(struct file *file, const struct iovec *iov,
 			break;
 		if (count) {
 			fuse_put_request(fc, req);
-			req = fuse_get_req(fc, FUSE_MAX_PAGES_PER_REQ);
+			req = fuse_get_req(fc, fuse_iter_npages(&ii));
 			if (IS_ERR(req))
 				break;
 		}