[PATCH v4 5/5] udmabuf: remove udmabuf_folio

[Huan Yang <link@vivo.com>]

Currently, udmabuf handles folio by creating an unpin list to record
each folio obtained from the list and unpinning them when released. To
maintain this approach, many data structures have been established.

However, maintaining this type of data structure requires a significant
amount of memory and traversing the list is a substantial overhead,
which is not friendly to the CPU cache.

We actually don't need to use unpin_list to unpin during release.
Instead, just use a folios array record each folio is ok.
Compare udmabuf_folio 24 byte, folio array is 8 byte. Even if array need
to be pgcnt*8, may waste some memory when use large folio.
The access of array is faster than list, also, if 4K, array can also
save memory than list.

Signed-off-by: Huan Yang <link@vivo.com>
---
 drivers/dma-buf/udmabuf.c | 80 ++++++++++++++++++---------------------
 1 file changed, 37 insertions(+), 43 deletions(-)

diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
index eb55bb4a5fcc..a45cec1f82b3 100644
--- a/drivers/dma-buf/udmabuf.c
+++ b/drivers/dma-buf/udmabuf.c
@@ -27,15 +27,21 @@ MODULE_PARM_DESC(size_limit_mb, "Max size of a dmabuf, in megabytes. Default is
 struct udmabuf {
 	pgoff_t pagecount;
 	struct folio **folios;
+
+	/**
+	 * Unlike folios, pinned_folios is only used for unpin.
+	 * So, nr_pinned is not the same to pagecount, the pinned_folios
+	 * only set each folio which already pinned when udmabuf_create.
+	 * Note that, since a folio may be pinned multiple times, each folio
+	 * can be added to pinned_folios multiple times, depending on how many
+	 * times the folio has been pinned when create.
+	 */
+	pgoff_t nr_pinned;
+	struct folio **pinned_folios;
+
 	struct sg_table *sg;
 	struct miscdevice *device;
 	pgoff_t *offsets;
-	struct list_head unpin_list;
-};
-
-struct udmabuf_folio {
-	struct folio *folio;
-	struct list_head list;
 };
 
 static vm_fault_t udmabuf_vm_fault(struct vm_fault *vmf)
@@ -189,32 +195,12 @@ static void unmap_udmabuf(struct dma_buf_attachment *at,
 	return put_sg_table(at->dev, sg, direction);
 }
 
-static void unpin_all_folios(struct list_head *unpin_list)
-{
-	struct udmabuf_folio *ubuf_folio;
-
-	while (!list_empty(unpin_list)) {
-		ubuf_folio = list_first_entry(unpin_list,
-					      struct udmabuf_folio, list);
-		unpin_folio(ubuf_folio->folio);
-
-		list_del(&ubuf_folio->list);
-		kfree(ubuf_folio);
-	}
-}
-
-static int add_to_unpin_list(struct list_head *unpin_list,
-			     struct folio *folio)
+static __always_inline void unpin_all_folios(struct udmabuf *ubuf)
 {
-	struct udmabuf_folio *ubuf_folio;
-
-	ubuf_folio = kzalloc(sizeof(*ubuf_folio), GFP_KERNEL);
-	if (!ubuf_folio)
-		return -ENOMEM;
+	pgoff_t i;
 
-	ubuf_folio->folio = folio;
-	list_add_tail(&ubuf_folio->list, unpin_list);
-	return 0;
+	for (i = 0; i < ubuf->nr_pinned; ++i)
+		unpin_folio(ubuf->pinned_folios[i]);
 }
 
 static void release_udmabuf(struct dma_buf *buf)
@@ -225,7 +211,8 @@ static void release_udmabuf(struct dma_buf *buf)
 	if (ubuf->sg)
 		put_sg_table(dev, ubuf->sg, DMA_BIDIRECTIONAL);
 
-	unpin_all_folios(&ubuf->unpin_list);
+	unpin_all_folios(ubuf);
+	kvfree(ubuf->pinned_folios);
 	kvfree(ubuf->offsets);
 	kvfree(ubuf->folios);
 	kfree(ubuf);
@@ -326,9 +313,9 @@ static int __udmabuf_pin_list_folios(struct udmabuf_create_item *item,
 				     struct folio **folios)
 {
 	struct file *memfd = NULL;
-	pgoff_t pgoff, ipgcnt, upgcnt = ubuf->pagecount;
+	pgoff_t pgoff, ipgcnt, upgcnt, nr_pinned;
 	u32 cur_folio, cur_pgcnt;
-	struct folio **ubuf_folios;
+	struct folio **ubuf_folios, **pinned_folios;
 	pgoff_t *ubuf_offsets;
 	long nr_folios;
 	loff_t end, start;
@@ -351,22 +338,21 @@ static int __udmabuf_pin_list_folios(struct udmabuf_create_item *item,
 	}
 
 	cur_pgcnt = 0;
+	nr_pinned = ubuf->nr_pinned;
+	upgcnt = ubuf->pagecount;
 	ubuf_folios = ubuf->folios;
 	ubuf_offsets = ubuf->offsets;
+	pinned_folios = ubuf->pinned_folios;
 
 	for (cur_folio = 0; cur_folio < nr_folios; ++cur_folio) {
 		pgoff_t subpgoff = pgoff;
 		long fsize = folio_size(folios[cur_folio]);
 
-		ret = add_to_unpin_list(&ubuf->unpin_list, folios[cur_folio]);
-		if (ret < 0) {
-			kfree(folios);
-			goto err;
-		}
+		pinned_folios[nr_pinned++] = folios[cur_folio];
 
 		for (; subpgoff < fsize; subpgoff += PAGE_SIZE) {
-			ubuf->folios[upgcnt] = folios[cur_folio];
-			ubuf->offsets[upgcnt] = subpgoff;
+			ubuf_folios[upgcnt] = folios[cur_folio];
+			ubuf_offsets[upgcnt] = subpgoff;
 			++upgcnt;
 
 			if (++cur_pgcnt >= ipgcnt)
@@ -381,12 +367,12 @@ static int __udmabuf_pin_list_folios(struct udmabuf_create_item *item,
 	}
 end:
 	ubuf->pagecount = upgcnt;
+	ubuf->nr_pinned = nr_pinned;
 	fput(memfd);
 
 	return 0;
 
 err:
-	ubuf->pagecount = upgcnt;
 	if (memfd)
 		fput(memfd);
 
@@ -407,7 +393,6 @@ static long udmabuf_create(struct miscdevice *device,
 	if (!ubuf)
 		return -ENOMEM;
 
-	INIT_LIST_HEAD(&ubuf->unpin_list);
 	pglimit = (size_limit_mb * 1024 * 1024) >> PAGE_SHIFT;
 	for (i = 0; i < head->count; i++) {
 		pgoff_t itempgcnt;
@@ -442,6 +427,14 @@ static long udmabuf_create(struct miscdevice *device,
 		goto err;
 	}
 
+	ubuf->pinned_folios = kvmalloc_array(pgcnt,
+					     sizeof(*ubuf->pinned_folios),
+					     GFP_KERNEL);
+	if (!ubuf->pinned_folios) {
+		ret = -ENOMEM;
+		goto err;
+	}
+
 	folios = kvmalloc_array(max_ipgcnt, sizeof(*folios), GFP_KERNEL);
 	if (!folios) {
 		ret = -ENOMEM;
@@ -463,8 +456,9 @@ static long udmabuf_create(struct miscdevice *device,
 	return ret;
 
 err:
-	unpin_all_folios(&ubuf->unpin_list);
+	unpin_all_folios(ubuf);
 	kvfree(folios);
+	kvfree(ubuf->pinned_folios);
 	kvfree(ubuf->offsets);
 	kvfree(ubuf->folios);
 	kfree(ubuf);
-- 
2.45.2