[PATCH v2 0/2] mm: batch free swaps for zap_pte_range()

[PATCH v2 0/2] mm: batch free swaps for zap_pte_range()

[Barry Song]

From: Barry Song <v-songbaohua@oppo.com>

Batch free swap slots for zap_pte_range(), making munmap three times
faster when the page table entries are filled with swap entries to
be freed. This is likely another advantage of using mTHP.

-v2:
  * cleanup the name of the instances of swap_info_struct, per
    Andrew, David;
  * refine the code to add fallback in the batch free function,
    Thanks for David's suggestion.
-v1:
  https://lore.kernel.org/all/20240806012409.61962-1-21cnbao@gmail.com/

Barry Song (2):
  mm: rename instances of swap_info_struct to meaningful 'si'
  mm: attempt to batch free swap entries for zap_pte_range()

 mm/swapfile.c | 412 ++++++++++++++++++++++++++++----------------------
 1 file changed, 234 insertions(+), 178 deletions(-)

-- 
2.34.1

[PATCH v2 1/2] mm: rename instances of swap_info_struct to meaningful 'si'

[Barry Song]

From: Barry Song <v-songbaohua@oppo.com>

"P" means "pointer to something", rename it to a more meaningful
identifier - "si".
We also have a case with the name "sis", rename it to "si" as
well.

Signed-off-by: Barry Song <v-songbaohua@oppo.com>
---
 mm/swapfile.c | 334 +++++++++++++++++++++++++-------------------------
 1 file changed, 167 insertions(+), 167 deletions(-)

diff --git a/mm/swapfile.c b/mm/swapfile.c
index ea023fc25d08..35cb58373493 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -532,7 +532,7 @@ static void free_cluster(struct swap_info_struct *si, struct swap_cluster_info *
  * added to free cluster list and its usage counter will be increased by 1.
  * Only used for initialization.
  */
-static void inc_cluster_info_page(struct swap_info_struct *p,
+static void inc_cluster_info_page(struct swap_info_struct *si,
 	struct swap_cluster_info *cluster_info, unsigned long page_nr)
 {
 	unsigned long idx = page_nr / SWAPFILE_CLUSTER;
@@ -553,28 +553,28 @@ static void inc_cluster_info_page(struct swap_info_struct *p,
  * which means no page in the cluster is in use, we can optionally discard
  * the cluster and add it to free cluster list.
  */
-static void dec_cluster_info_page(struct swap_info_struct *p,
+static void dec_cluster_info_page(struct swap_info_struct *si,
 				  struct swap_cluster_info *ci, int nr_pages)
 {
-	if (!p->cluster_info)
+	if (!si->cluster_info)
 		return;
 
 	VM_BUG_ON(ci->count < nr_pages);
 	VM_BUG_ON(cluster_is_free(ci));
-	lockdep_assert_held(&p->lock);
+	lockdep_assert_held(&si->lock);
 	lockdep_assert_held(&ci->lock);
 	ci->count -= nr_pages;
 
 	if (!ci->count) {
-		free_cluster(p, ci);
+		free_cluster(si, ci);
 		return;
 	}
 
 	if (!(ci->flags & CLUSTER_FLAG_NONFULL)) {
 		VM_BUG_ON(ci->flags & CLUSTER_FLAG_FREE);
 		if (ci->flags & CLUSTER_FLAG_FRAG)
-			p->frag_cluster_nr[ci->order]--;
-		list_move_tail(&ci->list, &p->nonfull_clusters[ci->order]);
+			si->frag_cluster_nr[ci->order]--;
+		list_move_tail(&ci->list, &si->nonfull_clusters[ci->order]);
 		ci->flags = CLUSTER_FLAG_NONFULL;
 	}
 }
@@ -872,19 +872,19 @@ static unsigned long cluster_alloc_swap_entry(struct swap_info_struct *si, int o
 	return found;
 }
 
-static void __del_from_avail_list(struct swap_info_struct *p)
+static void __del_from_avail_list(struct swap_info_struct *si)
 {
 	int nid;
 
-	assert_spin_locked(&p->lock);
+	assert_spin_locked(&si->lock);
 	for_each_node(nid)
-		plist_del(&p->avail_lists[nid], &swap_avail_heads[nid]);
+		plist_del(&si->avail_lists[nid], &swap_avail_heads[nid]);
 }
 
-static void del_from_avail_list(struct swap_info_struct *p)
+static void del_from_avail_list(struct swap_info_struct *si)
 {
 	spin_lock(&swap_avail_lock);
-	__del_from_avail_list(p);
+	__del_from_avail_list(si);
 	spin_unlock(&swap_avail_lock);
 }
 
@@ -905,13 +905,13 @@ static void swap_range_alloc(struct swap_info_struct *si, unsigned long offset,
 	}
 }
 
-static void add_to_avail_list(struct swap_info_struct *p)
+static void add_to_avail_list(struct swap_info_struct *si)
 {
 	int nid;
 
 	spin_lock(&swap_avail_lock);
 	for_each_node(nid)
-		plist_add(&p->avail_lists[nid], &swap_avail_heads[nid]);
+		plist_add(&si->avail_lists[nid], &swap_avail_heads[nid]);
 	spin_unlock(&swap_avail_lock);
 }
 
@@ -1291,22 +1291,22 @@ int get_swap_pages(int n_goal, swp_entry_t swp_entries[], int entry_order)
 
 static struct swap_info_struct *_swap_info_get(swp_entry_t entry)
 {
-	struct swap_info_struct *p;
+	struct swap_info_struct *si;
 	unsigned long offset;
 
 	if (!entry.val)
 		goto out;
-	p = swp_swap_info(entry);
-	if (!p)
+	si = swp_swap_info(entry);
+	if (!si)
 		goto bad_nofile;
-	if (data_race(!(p->flags & SWP_USED)))
+	if (data_race(!(si->flags & SWP_USED)))
 		goto bad_device;
 	offset = swp_offset(entry);
-	if (offset >= p->max)
+	if (offset >= si->max)
 		goto bad_offset;
-	if (data_race(!p->swap_map[swp_offset(entry)]))
+	if (data_race(!si->swap_map[swp_offset(entry)]))
 		goto bad_free;
-	return p;
+	return si;
 
 bad_free:
 	pr_err("%s: %s%08lx\n", __func__, Unused_offset, entry.val);
@@ -1339,14 +1339,14 @@ static struct swap_info_struct *swap_info_get_cont(swp_entry_t entry,
 	return p;
 }
 
-static unsigned char __swap_entry_free_locked(struct swap_info_struct *p,
+static unsigned char __swap_entry_free_locked(struct swap_info_struct *si,
 					      unsigned long offset,
 					      unsigned char usage)
 {
 	unsigned char count;
 	unsigned char has_cache;
 
-	count = p->swap_map[offset];
+	count = si->swap_map[offset];
 
 	has_cache = count & SWAP_HAS_CACHE;
 	count &= ~SWAP_HAS_CACHE;
@@ -1362,7 +1362,7 @@ static unsigned char __swap_entry_free_locked(struct swap_info_struct *p,
 		count = 0;
 	} else if ((count & ~COUNT_CONTINUED) <= SWAP_MAP_MAX) {
 		if (count == COUNT_CONTINUED) {
-			if (swap_count_continued(p, offset, count))
+			if (swap_count_continued(si, offset, count))
 				count = SWAP_MAP_MAX | COUNT_CONTINUED;
 			else
 				count = SWAP_MAP_MAX;
@@ -1372,9 +1372,9 @@ static unsigned char __swap_entry_free_locked(struct swap_info_struct *p,
 
 	usage = count | has_cache;
 	if (usage)
-		WRITE_ONCE(p->swap_map[offset], usage);
+		WRITE_ONCE(si->swap_map[offset], usage);
 	else
-		WRITE_ONCE(p->swap_map[offset], SWAP_HAS_CACHE);
+		WRITE_ONCE(si->swap_map[offset], SWAP_HAS_CACHE);
 
 	return usage;
 }
@@ -1453,16 +1453,16 @@ struct swap_info_struct *get_swap_device(swp_entry_t entry)
 	return NULL;
 }
 
-static unsigned char __swap_entry_free(struct swap_info_struct *p,
+static unsigned char __swap_entry_free(struct swap_info_struct *si,
 				       swp_entry_t entry)
 {
 	struct swap_cluster_info *ci;
 	unsigned long offset = swp_offset(entry);
 	unsigned char usage;
 
-	ci = lock_cluster_or_swap_info(p, offset);
-	usage = __swap_entry_free_locked(p, offset, 1);
-	unlock_cluster_or_swap_info(p, ci);
+	ci = lock_cluster_or_swap_info(si, offset);
+	usage = __swap_entry_free_locked(si, offset, 1);
+	unlock_cluster_or_swap_info(si, ci);
 	if (!usage)
 		free_swap_slot(entry);
 
@@ -1473,27 +1473,27 @@ static unsigned char __swap_entry_free(struct swap_info_struct *p,
  * Drop the last HAS_CACHE flag of swap entries, caller have to
  * ensure all entries belong to the same cgroup.
  */
-static void swap_entry_range_free(struct swap_info_struct *p, swp_entry_t entry,
+static void swap_entry_range_free(struct swap_info_struct *si, swp_entry_t entry,
 				  unsigned int nr_pages)
 {
 	unsigned long offset = swp_offset(entry);
-	unsigned char *map = p->swap_map + offset;
+	unsigned char *map = si->swap_map + offset;
 	unsigned char *map_end = map + nr_pages;
 	struct swap_cluster_info *ci;
 
-	ci = lock_cluster(p, offset);
+	ci = lock_cluster(si, offset);
 	do {
 		VM_BUG_ON(*map != SWAP_HAS_CACHE);
 		*map = 0;
 	} while (++map < map_end);
-	dec_cluster_info_page(p, ci, nr_pages);
+	dec_cluster_info_page(si, ci, nr_pages);
 	unlock_cluster(ci);
 
 	mem_cgroup_uncharge_swap(entry, nr_pages);
-	swap_range_free(p, offset, nr_pages);
+	swap_range_free(si, offset, nr_pages);
 }
 
-static void cluster_swap_free_nr(struct swap_info_struct *sis,
+static void cluster_swap_free_nr(struct swap_info_struct *si,
 		unsigned long offset, int nr_pages,
 		unsigned char usage)
 {
@@ -1501,26 +1501,26 @@ static void cluster_swap_free_nr(struct swap_info_struct *sis,
 	DECLARE_BITMAP(to_free, BITS_PER_LONG) = { 0 };
 	int i, nr;
 
-	ci = lock_cluster_or_swap_info(sis, offset);
+	ci = lock_cluster_or_swap_info(si, offset);
 	while (nr_pages) {
 		nr = min(BITS_PER_LONG, nr_pages);
 		for (i = 0; i < nr; i++) {
-			if (!__swap_entry_free_locked(sis, offset + i, usage))
+			if (!__swap_entry_free_locked(si, offset + i, usage))
 				bitmap_set(to_free, i, 1);
 		}
 		if (!bitmap_empty(to_free, BITS_PER_LONG)) {
-			unlock_cluster_or_swap_info(sis, ci);
+			unlock_cluster_or_swap_info(si, ci);
 			for_each_set_bit(i, to_free, BITS_PER_LONG)
-				free_swap_slot(swp_entry(sis->type, offset + i));
+				free_swap_slot(swp_entry(si->type, offset + i));
 			if (nr == nr_pages)
 				return;
 			bitmap_clear(to_free, 0, BITS_PER_LONG);
-			ci = lock_cluster_or_swap_info(sis, offset);
+			ci = lock_cluster_or_swap_info(si, offset);
 		}
 		offset += nr;
 		nr_pages -= nr;
 	}
-	unlock_cluster_or_swap_info(sis, ci);
+	unlock_cluster_or_swap_info(si, ci);
 }
 
 /*
@@ -1646,28 +1646,28 @@ int swap_swapcount(struct swap_info_struct *si, swp_entry_t entry)
 int swp_swapcount(swp_entry_t entry)
 {
 	int count, tmp_count, n;
-	struct swap_info_struct *p;
+	struct swap_info_struct *si;
 	struct swap_cluster_info *ci;
 	struct page *page;
 	pgoff_t offset;
 	unsigned char *map;
 
-	p = _swap_info_get(entry);
-	if (!p)
+	si = _swap_info_get(entry);
+	if (!si)
 		return 0;
 
 	offset = swp_offset(entry);
 
-	ci = lock_cluster_or_swap_info(p, offset);
+	ci = lock_cluster_or_swap_info(si, offset);
 
-	count = swap_count(p->swap_map[offset]);
+	count = swap_count(si->swap_map[offset]);
 	if (!(count & COUNT_CONTINUED))
 		goto out;
 
 	count &= ~COUNT_CONTINUED;
 	n = SWAP_MAP_MAX + 1;
 
-	page = vmalloc_to_page(p->swap_map + offset);
+	page = vmalloc_to_page(si->swap_map + offset);
 	offset &= ~PAGE_MASK;
 	VM_BUG_ON(page_private(page) != SWP_CONTINUED);
 
@@ -1681,7 +1681,7 @@ int swp_swapcount(swp_entry_t entry)
 		n *= (SWAP_CONT_MAX + 1);
 	} while (tmp_count & COUNT_CONTINUED);
 out:
-	unlock_cluster_or_swap_info(p, ci);
+	unlock_cluster_or_swap_info(si, ci);
 	return count;
 }
 
@@ -2542,52 +2542,52 @@ static int setup_swap_extents(struct swap_info_struct *sis, sector_t *span)
 	return generic_swapfile_activate(sis, swap_file, span);
 }
 
-static int swap_node(struct swap_info_struct *p)
+static int swap_node(struct swap_info_struct *si)
 {
 	struct block_device *bdev;
 
-	if (p->bdev)
-		bdev = p->bdev;
+	if (si->bdev)
+		bdev = si->bdev;
 	else
-		bdev = p->swap_file->f_inode->i_sb->s_bdev;
+		bdev = si->swap_file->f_inode->i_sb->s_bdev;
 
 	return bdev ? bdev->bd_disk->node_id : NUMA_NO_NODE;
 }
 
-static void setup_swap_info(struct swap_info_struct *p, int prio,
+static void setup_swap_info(struct swap_info_struct *si, int prio,
 			    unsigned char *swap_map,
 			    struct swap_cluster_info *cluster_info)
 {
 	int i;
 
 	if (prio >= 0)
-		p->prio = prio;
+		si->prio = prio;
 	else
-		p->prio = --least_priority;
+		si->prio = --least_priority;
 	/*
 	 * the plist prio is negated because plist ordering is
 	 * low-to-high, while swap ordering is high-to-low
 	 */
-	p->list.prio = -p->prio;
+	si->list.prio = -si->prio;
 	for_each_node(i) {
-		if (p->prio >= 0)
-			p->avail_lists[i].prio = -p->prio;
+		if (si->prio >= 0)
+			si->avail_lists[i].prio = -si->prio;
 		else {
-			if (swap_node(p) == i)
-				p->avail_lists[i].prio = 1;
+			if (swap_node(si) == i)
+				si->avail_lists[i].prio = 1;
 			else
-				p->avail_lists[i].prio = -p->prio;
+				si->avail_lists[i].prio = -si->prio;
 		}
 	}
-	p->swap_map = swap_map;
-	p->cluster_info = cluster_info;
+	si->swap_map = swap_map;
+	si->cluster_info = cluster_info;
 }
 
-static void _enable_swap_info(struct swap_info_struct *p)
+static void _enable_swap_info(struct swap_info_struct *si)
 {
-	p->flags |= SWP_WRITEOK;
-	atomic_long_add(p->pages, &nr_swap_pages);
-	total_swap_pages += p->pages;
+	si->flags |= SWP_WRITEOK;
+	atomic_long_add(si->pages, &nr_swap_pages);
+	total_swap_pages += si->pages;
 
 	assert_spin_locked(&swap_lock);
 	/*
@@ -2600,40 +2600,40 @@ static void _enable_swap_info(struct swap_info_struct *p)
 	 * which allocates swap pages from the highest available priority
 	 * swap_info_struct.
 	 */
-	plist_add(&p->list, &swap_active_head);
+	plist_add(&si->list, &swap_active_head);
 
 	/* add to available list iff swap device is not full */
-	if (p->highest_bit)
-		add_to_avail_list(p);
+	if (si->highest_bit)
+		add_to_avail_list(si);
 }
 
-static void enable_swap_info(struct swap_info_struct *p, int prio,
+static void enable_swap_info(struct swap_info_struct *si, int prio,
 				unsigned char *swap_map,
 				struct swap_cluster_info *cluster_info)
 {
 	spin_lock(&swap_lock);
-	spin_lock(&p->lock);
-	setup_swap_info(p, prio, swap_map, cluster_info);
-	spin_unlock(&p->lock);
+	spin_lock(&si->lock);
+	setup_swap_info(si, prio, swap_map, cluster_info);
+	spin_unlock(&si->lock);
 	spin_unlock(&swap_lock);
 	/*
 	 * Finished initializing swap device, now it's safe to reference it.
 	 */
-	percpu_ref_resurrect(&p->users);
+	percpu_ref_resurrect(&si->users);
 	spin_lock(&swap_lock);
-	spin_lock(&p->lock);
-	_enable_swap_info(p);
-	spin_unlock(&p->lock);
+	spin_lock(&si->lock);
+	_enable_swap_info(si);
+	spin_unlock(&si->lock);
 	spin_unlock(&swap_lock);
 }
 
-static void reinsert_swap_info(struct swap_info_struct *p)
+static void reinsert_swap_info(struct swap_info_struct *si)
 {
 	spin_lock(&swap_lock);
-	spin_lock(&p->lock);
-	setup_swap_info(p, p->prio, p->swap_map, p->cluster_info);
-	_enable_swap_info(p);
-	spin_unlock(&p->lock);
+	spin_lock(&si->lock);
+	setup_swap_info(si, si->prio, si->swap_map, si->cluster_info);
+	_enable_swap_info(si);
+	spin_unlock(&si->lock);
 	spin_unlock(&swap_lock);
 }
 
@@ -3019,20 +3019,20 @@ static struct swap_info_struct *alloc_swap_info(void)
 	return p;
 }
 
-static int claim_swapfile(struct swap_info_struct *p, struct inode *inode)
+static int claim_swapfile(struct swap_info_struct *si, struct inode *inode)
 {
 	if (S_ISBLK(inode->i_mode)) {
-		p->bdev = I_BDEV(inode);
+		si->bdev = I_BDEV(inode);
 		/*
 		 * Zoned block devices contain zones that have a sequential
 		 * write only restriction.  Hence zoned block devices are not
 		 * suitable for swapping.  Disallow them here.
 		 */
-		if (bdev_is_zoned(p->bdev))
+		if (bdev_is_zoned(si->bdev))
 			return -EINVAL;
-		p->flags |= SWP_BLKDEV;
+		si->flags |= SWP_BLKDEV;
 	} else if (S_ISREG(inode->i_mode)) {
-		p->bdev = inode->i_sb->s_bdev;
+		si->bdev = inode->i_sb->s_bdev;
 	}
 
 	return 0;
@@ -3067,7 +3067,7 @@ __weak unsigned long arch_max_swapfile_size(void)
 	return generic_max_swapfile_size();
 }
 
-static unsigned long read_swap_header(struct swap_info_struct *p,
+static unsigned long read_swap_header(struct swap_info_struct *si,
 					union swap_header *swap_header,
 					struct inode *inode)
 {
@@ -3098,9 +3098,9 @@ static unsigned long read_swap_header(struct swap_info_struct *p,
 		return 0;
 	}
 
-	p->lowest_bit  = 1;
-	p->cluster_next = 1;
-	p->cluster_nr = 0;
+	si->lowest_bit  = 1;
+	si->cluster_next = 1;
+	si->cluster_nr = 0;
 
 	maxpages = swapfile_maximum_size;
 	last_page = swap_header->info.last_page;
@@ -3118,7 +3118,7 @@ static unsigned long read_swap_header(struct swap_info_struct *p,
 		if ((unsigned int)maxpages == 0)
 			maxpages = UINT_MAX;
 	}
-	p->highest_bit = maxpages - 1;
+	si->highest_bit = maxpages - 1;
 
 	if (!maxpages)
 		return 0;
@@ -3142,7 +3142,7 @@ static unsigned long read_swap_header(struct swap_info_struct *p,
 #define SWAP_CLUSTER_COLS						\
 	max_t(unsigned int, SWAP_CLUSTER_INFO_COLS, SWAP_CLUSTER_SPACE_COLS)
 
-static int setup_swap_map_and_extents(struct swap_info_struct *p,
+static int setup_swap_map_and_extents(struct swap_info_struct *si,
 					union swap_header *swap_header,
 					unsigned char *swap_map,
 					struct swap_cluster_info *cluster_info,
@@ -3153,19 +3153,19 @@ static int setup_swap_map_and_extents(struct swap_info_struct *p,
 	unsigned int nr_good_pages;
 	int nr_extents;
 	unsigned long nr_clusters = DIV_ROUND_UP(maxpages, SWAPFILE_CLUSTER);
-	unsigned long col = p->cluster_next / SWAPFILE_CLUSTER % SWAP_CLUSTER_COLS;
+	unsigned long col = si->cluster_next / SWAPFILE_CLUSTER % SWAP_CLUSTER_COLS;
 	unsigned long i, idx;
 
 	nr_good_pages = maxpages - 1;	/* omit header page */
 
-	INIT_LIST_HEAD(&p->free_clusters);
-	INIT_LIST_HEAD(&p->full_clusters);
-	INIT_LIST_HEAD(&p->discard_clusters);
+	INIT_LIST_HEAD(&si->free_clusters);
+	INIT_LIST_HEAD(&si->full_clusters);
+	INIT_LIST_HEAD(&si->discard_clusters);
 
 	for (i = 0; i < SWAP_NR_ORDERS; i++) {
-		INIT_LIST_HEAD(&p->nonfull_clusters[i]);
-		INIT_LIST_HEAD(&p->frag_clusters[i]);
-		p->frag_cluster_nr[i] = 0;
+		INIT_LIST_HEAD(&si->nonfull_clusters[i]);
+		INIT_LIST_HEAD(&si->frag_clusters[i]);
+		si->frag_cluster_nr[i] = 0;
 	}
 
 	for (i = 0; i < swap_header->info.nr_badpages; i++) {
@@ -3179,13 +3179,13 @@ static int setup_swap_map_and_extents(struct swap_info_struct *p,
 			 * Haven't marked the cluster free yet, no list
 			 * operation involved
 			 */
-			inc_cluster_info_page(p, cluster_info, page_nr);
+			inc_cluster_info_page(si, cluster_info, page_nr);
 		}
 	}
 
 	/* Haven't marked the cluster free yet, no list operation involved */
 	for (i = maxpages; i < round_up(maxpages, SWAPFILE_CLUSTER); i++)
-		inc_cluster_info_page(p, cluster_info, i);
+		inc_cluster_info_page(si, cluster_info, i);
 
 	if (nr_good_pages) {
 		swap_map[0] = SWAP_MAP_BAD;
@@ -3193,13 +3193,13 @@ static int setup_swap_map_and_extents(struct swap_info_struct *p,
 		 * Not mark the cluster free yet, no list
 		 * operation involved
 		 */
-		inc_cluster_info_page(p, cluster_info, 0);
-		p->max = maxpages;
-		p->pages = nr_good_pages;
-		nr_extents = setup_swap_extents(p, span);
+		inc_cluster_info_page(si, cluster_info, 0);
+		si->max = maxpages;
+		si->pages = nr_good_pages;
+		nr_extents = setup_swap_extents(si, span);
 		if (nr_extents < 0)
 			return nr_extents;
-		nr_good_pages = p->pages;
+		nr_good_pages = si->pages;
 	}
 	if (!nr_good_pages) {
 		pr_warn("Empty swap-file\n");
@@ -3223,11 +3223,11 @@ static int setup_swap_map_and_extents(struct swap_info_struct *p,
 				continue;
 			if (ci->count) {
 				ci->flags = CLUSTER_FLAG_NONFULL;
-				list_add_tail(&ci->list, &p->nonfull_clusters[0]);
+				list_add_tail(&ci->list, &si->nonfull_clusters[0]);
 				continue;
 			}
 			ci->flags = CLUSTER_FLAG_FREE;
-			list_add_tail(&ci->list, &p->free_clusters);
+			list_add_tail(&ci->list, &si->free_clusters);
 		}
 	}
 	return nr_extents;
@@ -3235,7 +3235,7 @@ static int setup_swap_map_and_extents(struct swap_info_struct *p,
 
 SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
 {
-	struct swap_info_struct *p;
+	struct swap_info_struct *si;
 	struct filename *name;
 	struct file *swap_file = NULL;
 	struct address_space *mapping;
@@ -3261,11 +3261,11 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
 	if (!swap_avail_heads)
 		return -ENOMEM;
 
-	p = alloc_swap_info();
-	if (IS_ERR(p))
-		return PTR_ERR(p);
+	si = alloc_swap_info();
+	if (IS_ERR(si))
+		return PTR_ERR(si);
 
-	INIT_WORK(&p->discard_work, swap_discard_work);
+	INIT_WORK(&si->discard_work, swap_discard_work);
 
 	name = getname(specialfile);
 	if (IS_ERR(name)) {
@@ -3280,12 +3280,12 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
 		goto bad_swap;
 	}
 
-	p->swap_file = swap_file;
+	si->swap_file = swap_file;
 	mapping = swap_file->f_mapping;
 	dentry = swap_file->f_path.dentry;
 	inode = mapping->host;
 
-	error = claim_swapfile(p, inode);
+	error = claim_swapfile(si, inode);
 	if (unlikely(error))
 		goto bad_swap;
 
@@ -3313,7 +3313,7 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
 	}
 	swap_header = kmap(page);
 
-	maxpages = read_swap_header(p, swap_header, inode);
+	maxpages = read_swap_header(si, swap_header, inode);
 	if (unlikely(!maxpages)) {
 		error = -EINVAL;
 		goto bad_swap_unlock_inode;
@@ -3326,19 +3326,19 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
 		goto bad_swap_unlock_inode;
 	}
 
-	if (p->bdev && bdev_stable_writes(p->bdev))
-		p->flags |= SWP_STABLE_WRITES;
+	if (si->bdev && bdev_stable_writes(si->bdev))
+		si->flags |= SWP_STABLE_WRITES;
 
-	if (p->bdev && bdev_synchronous(p->bdev))
-		p->flags |= SWP_SYNCHRONOUS_IO;
+	if (si->bdev && bdev_synchronous(si->bdev))
+		si->flags |= SWP_SYNCHRONOUS_IO;
 
-	if (p->bdev && bdev_nonrot(p->bdev)) {
+	if (si->bdev && bdev_nonrot(si->bdev)) {
 		int cpu, i;
 		unsigned long ci, nr_cluster;
 
-		p->flags |= SWP_SOLIDSTATE;
-		p->cluster_next_cpu = alloc_percpu(unsigned int);
-		if (!p->cluster_next_cpu) {
+		si->flags |= SWP_SOLIDSTATE;
+		si->cluster_next_cpu = alloc_percpu(unsigned int);
+		if (!si->cluster_next_cpu) {
 			error = -ENOMEM;
 			goto bad_swap_unlock_inode;
 		}
@@ -3347,8 +3347,8 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
 		 * SSD
 		 */
 		for_each_possible_cpu(cpu) {
-			per_cpu(*p->cluster_next_cpu, cpu) =
-				get_random_u32_inclusive(1, p->highest_bit);
+			per_cpu(*si->cluster_next_cpu, cpu) =
+				get_random_u32_inclusive(1, si->highest_bit);
 		}
 		nr_cluster = DIV_ROUND_UP(maxpages, SWAPFILE_CLUSTER);
 
@@ -3362,15 +3362,15 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
 		for (ci = 0; ci < nr_cluster; ci++)
 			spin_lock_init(&((cluster_info + ci)->lock));
 
-		p->percpu_cluster = alloc_percpu(struct percpu_cluster);
-		if (!p->percpu_cluster) {
+		si->percpu_cluster = alloc_percpu(struct percpu_cluster);
+		if (!si->percpu_cluster) {
 			error = -ENOMEM;
 			goto bad_swap_unlock_inode;
 		}
 		for_each_possible_cpu(cpu) {
 			struct percpu_cluster *cluster;
 
-			cluster = per_cpu_ptr(p->percpu_cluster, cpu);
+			cluster = per_cpu_ptr(si->percpu_cluster, cpu);
 			for (i = 0; i < SWAP_NR_ORDERS; i++)
 				cluster->next[i] = SWAP_NEXT_INVALID;
 		}
@@ -3379,11 +3379,11 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
 		inced_nr_rotate_swap = true;
 	}
 
-	error = swap_cgroup_swapon(p->type, maxpages);
+	error = swap_cgroup_swapon(si->type, maxpages);
 	if (error)
 		goto bad_swap_unlock_inode;
 
-	nr_extents = setup_swap_map_and_extents(p, swap_header, swap_map,
+	nr_extents = setup_swap_map_and_extents(si, swap_header, swap_map,
 		cluster_info, maxpages, &span);
 	if (unlikely(nr_extents < 0)) {
 		error = nr_extents;
@@ -3391,14 +3391,14 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
 	}
 
 	if ((swap_flags & SWAP_FLAG_DISCARD) &&
-	    p->bdev && bdev_max_discard_sectors(p->bdev)) {
+	    si->bdev && bdev_max_discard_sectors(si->bdev)) {
 		/*
 		 * When discard is enabled for swap with no particular
 		 * policy flagged, we set all swap discard flags here in
 		 * order to sustain backward compatibility with older
 		 * swapon(8) releases.
 		 */
-		p->flags |= (SWP_DISCARDABLE | SWP_AREA_DISCARD |
+		si->flags |= (SWP_DISCARDABLE | SWP_AREA_DISCARD |
 			     SWP_PAGE_DISCARD);
 
 		/*
@@ -3408,24 +3408,24 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
 		 * Now it's time to adjust the p->flags accordingly.
 		 */
 		if (swap_flags & SWAP_FLAG_DISCARD_ONCE)
-			p->flags &= ~SWP_PAGE_DISCARD;
+			si->flags &= ~SWP_PAGE_DISCARD;
 		else if (swap_flags & SWAP_FLAG_DISCARD_PAGES)
-			p->flags &= ~SWP_AREA_DISCARD;
+			si->flags &= ~SWP_AREA_DISCARD;
 
 		/* issue a swapon-time discard if it's still required */
-		if (p->flags & SWP_AREA_DISCARD) {
-			int err = discard_swap(p);
+		if (si->flags & SWP_AREA_DISCARD) {
+			int err = discard_swap(si);
 			if (unlikely(err))
 				pr_err("swapon: discard_swap(%p): %d\n",
-					p, err);
+					si, err);
 		}
 	}
 
-	error = init_swap_address_space(p->type, maxpages);
+	error = init_swap_address_space(si->type, maxpages);
 	if (error)
 		goto bad_swap_unlock_inode;
 
-	error = zswap_swapon(p->type, maxpages);
+	error = zswap_swapon(si->type, maxpages);
 	if (error)
 		goto free_swap_address_space;
 
@@ -3445,15 +3445,15 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
 	if (swap_flags & SWAP_FLAG_PREFER)
 		prio =
 		  (swap_flags & SWAP_FLAG_PRIO_MASK) >> SWAP_FLAG_PRIO_SHIFT;
-	enable_swap_info(p, prio, swap_map, cluster_info);
+	enable_swap_info(si, prio, swap_map, cluster_info);
 
 	pr_info("Adding %uk swap on %s.  Priority:%d extents:%d across:%lluk %s%s%s%s\n",
-		K(p->pages), name->name, p->prio, nr_extents,
+		K(si->pages), name->name, si->prio, nr_extents,
 		K((unsigned long long)span),
-		(p->flags & SWP_SOLIDSTATE) ? "SS" : "",
-		(p->flags & SWP_DISCARDABLE) ? "D" : "",
-		(p->flags & SWP_AREA_DISCARD) ? "s" : "",
-		(p->flags & SWP_PAGE_DISCARD) ? "c" : "");
+		(si->flags & SWP_SOLIDSTATE) ? "SS" : "",
+		(si->flags & SWP_DISCARDABLE) ? "D" : "",
+		(si->flags & SWP_AREA_DISCARD) ? "s" : "",
+		(si->flags & SWP_PAGE_DISCARD) ? "c" : "");
 
 	mutex_unlock(&swapon_mutex);
 	atomic_inc(&proc_poll_event);
@@ -3462,22 +3462,22 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
 	error = 0;
 	goto out;
 free_swap_zswap:
-	zswap_swapoff(p->type);
+	zswap_swapoff(si->type);
 free_swap_address_space:
-	exit_swap_address_space(p->type);
+	exit_swap_address_space(si->type);
 bad_swap_unlock_inode:
 	inode_unlock(inode);
 bad_swap:
-	free_percpu(p->percpu_cluster);
-	p->percpu_cluster = NULL;
-	free_percpu(p->cluster_next_cpu);
-	p->cluster_next_cpu = NULL;
+	free_percpu(si->percpu_cluster);
+	si->percpu_cluster = NULL;
+	free_percpu(si->cluster_next_cpu);
+	si->cluster_next_cpu = NULL;
 	inode = NULL;
-	destroy_swap_extents(p);
-	swap_cgroup_swapoff(p->type);
+	destroy_swap_extents(si);
+	swap_cgroup_swapoff(si->type);
 	spin_lock(&swap_lock);
-	p->swap_file = NULL;
-	p->flags = 0;
+	si->swap_file = NULL;
+	si->flags = 0;
 	spin_unlock(&swap_lock);
 	vfree(swap_map);
 	kvfree(cluster_info);
@@ -3529,23 +3529,23 @@ void si_swapinfo(struct sysinfo *val)
  */
 static int __swap_duplicate(swp_entry_t entry, unsigned char usage, int nr)
 {
-	struct swap_info_struct *p;
+	struct swap_info_struct *si;
 	struct swap_cluster_info *ci;
 	unsigned long offset;
 	unsigned char count;
 	unsigned char has_cache;
 	int err, i;
 
-	p = swp_swap_info(entry);
+	si = swp_swap_info(entry);
 
 	offset = swp_offset(entry);
 	VM_WARN_ON(nr > SWAPFILE_CLUSTER - offset % SWAPFILE_CLUSTER);
 	VM_WARN_ON(usage == 1 && nr > 1);
-	ci = lock_cluster_or_swap_info(p, offset);
+	ci = lock_cluster_or_swap_info(si, offset);
 
 	err = 0;
 	for (i = 0; i < nr; i++) {
-		count = p->swap_map[offset + i];
+		count = si->swap_map[offset + i];
 
 		/*
 		 * swapin_readahead() doesn't check if a swap entry is valid, so the
@@ -3573,7 +3573,7 @@ static int __swap_duplicate(swp_entry_t entry, unsigned char usage, int nr)
 	}
 
 	for (i = 0; i < nr; i++) {
-		count = p->swap_map[offset + i];
+		count = si->swap_map[offset + i];
 		has_cache = count & SWAP_HAS_CACHE;
 		count &= ~SWAP_HAS_CACHE;
 
@@ -3581,7 +3581,7 @@ static int __swap_duplicate(swp_entry_t entry, unsigned char usage, int nr)
 			has_cache = SWAP_HAS_CACHE;
 		else if ((count & ~COUNT_CONTINUED) < SWAP_MAP_MAX)
 			count += usage;
-		else if (swap_count_continued(p, offset + i, count))
+		else if (swap_count_continued(si, offset + i, count))
 			count = COUNT_CONTINUED;
 		else {
 			/*
@@ -3592,11 +3592,11 @@ static int __swap_duplicate(swp_entry_t entry, unsigned char usage, int nr)
 			goto unlock_out;
 		}
 
-		WRITE_ONCE(p->swap_map[offset + i], count | has_cache);
+		WRITE_ONCE(si->swap_map[offset + i], count | has_cache);
 	}
 
 unlock_out:
-	unlock_cluster_or_swap_info(p, ci);
+	unlock_cluster_or_swap_info(si, ci);
 	return err;
 }
 
-- 
2.34.1

Re: [PATCH v2 1/2] mm: rename instances of swap_info_struct to meaningful 'si'

[David Hildenbrand]

On 07.08.24 10:25, Barry Song wrote:
> From: Barry Song <v-songbaohua@oppo.com>
> 
> "P" means "pointer to something", rename it to a more meaningful
> identifier - "si".
> We also have a case with the name "sis", rename it to "si" as
> well.
> 
> Signed-off-by: Barry Song <v-songbaohua@oppo.com>
> ---
>   mm/swapfile.c | 334 +++++++++++++++++++++++++-------------------------
>   1 file changed, 167 insertions(+), 167 deletions(-)

It's a bit of churn but all straight forward. No opinion against it from 
my side.

Acked-by: David Hildenbrand <david@redhat.com>

-- 
Cheers,

David / dhildenb

[PATCH v2 2/2] mm: attempt to batch free swap entries for zap_pte_range()

[Barry Song]

From: Barry Song <v-songbaohua@oppo.com>

Zhiguo reported that swap release could be a serious bottleneck
during process exits[1]. With mTHP, we have the opportunity to
batch free swaps.
Thanks to the work of Chris and Kairui[2], I was able to achieve
this optimization with minimal code changes by building on their
efforts.
If swap_count is 1, which is likely true as most anon memory are
private, we can free all contiguous swap slots all together.

Ran the below test program for measuring the bandwidth of munmap
using zRAM and 64KiB mTHP:

 #include <sys/mman.h>
 #include <sys/time.h>
 #include <stdlib.h>

 unsigned long long tv_to_ms(struct timeval tv)
 {
        return tv.tv_sec * 1000 + tv.tv_usec / 1000;
 }

 main()
 {
        struct timeval tv_b, tv_e;
        int i;
 #define SIZE 1024*1024*1024
        void *p = mmap(NULL, SIZE, PROT_READ | PROT_WRITE,
                                MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
        if (!p) {
                perror("fail to get memory");
                exit(-1);
        }

        madvise(p, SIZE, MADV_HUGEPAGE);
        memset(p, 0x11, SIZE); /* write to get mem */

        madvise(p, SIZE, MADV_PAGEOUT);

        gettimeofday(&tv_b, NULL);
        munmap(p, SIZE);
        gettimeofday(&tv_e, NULL);

        printf("munmap in bandwidth: %ld bytes/ms\n",
                        SIZE/(tv_to_ms(tv_e) - tv_to_ms(tv_b)));
 }

The result is as below (munmap bandwidth):
                mm-unstable  mm-unstable-with-patch
   round1       21053761      63161283
   round2       21053761      63161283
   round3       21053761      63161283
   round4       20648881      67108864
   round5       20648881      67108864

munmap bandwidth becomes 3X faster.

[1] https://lore.kernel.org/linux-mm/20240731133318.527-1-justinjiang@vivo.com/
[2] https://lore.kernel.org/linux-mm/20240730-swap-allocator-v5-0-cb9c148b9297@kernel.org/

Cc: Kairui Song <kasong@tencent.com>
Cc: Chris Li <chrisl@kernel.org>
Cc: "Huang, Ying" <ying.huang@intel.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Kalesh Singh <kaleshsingh@google.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: David Hildenbrand <david@redhat.com>
Signed-off-by: Barry Song <v-songbaohua@oppo.com>
---
 mm/swapfile.c | 78 +++++++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 67 insertions(+), 11 deletions(-)

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 35cb58373493..25c3f98fa8d5 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -156,6 +156,25 @@ static bool swap_is_has_cache(struct swap_info_struct *si,
 	return true;
 }
 
+static bool swap_is_last_map(struct swap_info_struct *si,
+			      unsigned long offset, int nr_pages,
+			      bool *has_cache)
+{
+	unsigned char *map = si->swap_map + offset;
+	unsigned char *map_end = map + nr_pages;
+	bool cached = false;
+
+	do {
+		if ((*map & ~SWAP_HAS_CACHE) != 1)
+			return false;
+		if (*map & SWAP_HAS_CACHE)
+			cached = true;
+	} while (++map < map_end);
+
+	*has_cache = cached;
+	return true;
+}
+
 /*
  * returns number of pages in the folio that backs the swap entry. If positive,
  * the folio was reclaimed. If negative, the folio was not reclaimed. If 0, no
@@ -1469,6 +1488,53 @@ static unsigned char __swap_entry_free(struct swap_info_struct *si,
 	return usage;
 }
 
+static bool __swap_entries_free(struct swap_info_struct *si,
+				swp_entry_t entry, int nr)
+{
+	unsigned long offset = swp_offset(entry);
+	unsigned int type = swp_type(entry);
+	struct swap_cluster_info *ci;
+	bool has_cache = false;
+	unsigned char count;
+	bool can_batch;
+	int i;
+
+	if (nr <= 1 || swap_count(data_race(si->swap_map[offset])) != 1)
+		goto fallback;
+	/* cross into another cluster */
+	if (nr > SWAPFILE_CLUSTER - offset % SWAPFILE_CLUSTER)
+		goto fallback;
+
+	ci = lock_cluster_or_swap_info(si, offset);
+	can_batch = swap_is_last_map(si, offset, nr, &has_cache);
+	if (can_batch) {
+		for (i = 0; i < nr; i++)
+			WRITE_ONCE(si->swap_map[offset + i], SWAP_HAS_CACHE);
+	}
+	unlock_cluster_or_swap_info(si, ci);
+
+	if (!can_batch)
+		goto fallback;
+	if (!has_cache) {
+		spin_lock(&si->lock);
+		swap_entry_range_free(si, entry, nr);
+		spin_unlock(&si->lock);
+	}
+	return has_cache;
+
+fallback:
+	for (i = 0; i  < nr; i++) {
+		if (data_race(si->swap_map[offset + i])) {
+			count = __swap_entry_free(si, swp_entry(type, offset + i));
+			if (count == SWAP_HAS_CACHE)
+				has_cache = true;
+		} else {
+			WARN_ON_ONCE(1);
+		}
+	}
+	return has_cache;
+}
+
 /*
  * Drop the last HAS_CACHE flag of swap entries, caller have to
  * ensure all entries belong to the same cgroup.
@@ -1792,11 +1858,9 @@ void free_swap_and_cache_nr(swp_entry_t entry, int nr)
 {
 	const unsigned long start_offset = swp_offset(entry);
 	const unsigned long end_offset = start_offset + nr;
-	unsigned int type = swp_type(entry);
 	struct swap_info_struct *si;
 	bool any_only_cache = false;
 	unsigned long offset;
-	unsigned char count;
 
 	if (non_swap_entry(entry))
 		return;
@@ -1811,15 +1875,7 @@ void free_swap_and_cache_nr(swp_entry_t entry, int nr)
 	/*
 	 * First free all entries in the range.
 	 */
-	for (offset = start_offset; offset < end_offset; offset++) {
-		if (data_race(si->swap_map[offset])) {
-			count = __swap_entry_free(si, swp_entry(type, offset));
-			if (count == SWAP_HAS_CACHE)
-				any_only_cache = true;
-		} else {
-			WARN_ON_ONCE(1);
-		}
-	}
+	any_only_cache = __swap_entries_free(si, entry, nr);
 
 	/*
 	 * Short-circuit the below loop if none of the entries had their
-- 
2.34.1

Re: [PATCH v2 2/2] mm: attempt to batch free swap entries for zap_pte_range()

[David Hildenbrand]

>   mm/swapfile.c | 78 +++++++++++++++++++++++++++++++++++++++++++--------
>   1 file changed, 67 insertions(+), 11 deletions(-)
> 
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index 35cb58373493..25c3f98fa8d5 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -156,6 +156,25 @@ static bool swap_is_has_cache(struct swap_info_struct *si,
>   	return true;
>   }
>   
> +static bool swap_is_last_map(struct swap_info_struct *si,
> +			      unsigned long offset, int nr_pages,
> +			      bool *has_cache)

Please use double tabs for indenting parameters on 2nd line on 
new/changed code:

		unsigned long offset, int nr_pages, bool *has_cache)

Results in less churn when renaming functions and we can frequently 
avoid some lines.

> +{
> +	unsigned char *map = si->swap_map + offset;
> +	unsigned char *map_end = map + nr_pages;
> +	bool cached = false;
> +
> +	do {
> +		if ((*map & ~SWAP_HAS_CACHE) != 1)
> +			return false;
> +		if (*map & SWAP_HAS_CACHE)
> +			cached = true;
> +	} while (++map < map_end);
> +
> +	*has_cache = cached;
> +	return true;
> +}
> +
>   /*
>    * returns number of pages in the folio that backs the swap entry. If positive,
>    * the folio was reclaimed. If negative, the folio was not reclaimed. If 0, no
> @@ -1469,6 +1488,53 @@ static unsigned char __swap_entry_free(struct swap_info_struct *si,
>   	return usage;
>   }
>   
> +static bool __swap_entries_free(struct swap_info_struct *si,
> +				swp_entry_t entry, int nr)

Dito.

> +{
> +	unsigned long offset = swp_offset(entry);
> +	unsigned int type = swp_type(entry);
> +	struct swap_cluster_info *ci;
> +	bool has_cache = false;
> +	unsigned char count;
> +	bool can_batch;
> +	int i;
> +
> +	if (nr <= 1 || swap_count(data_race(si->swap_map[offset])) != 1)
> +		goto fallback;
> +	/* cross into another cluster */
> +	if (nr > SWAPFILE_CLUSTER - offset % SWAPFILE_CLUSTER)
> +		goto fallback;
> +
> +	ci = lock_cluster_or_swap_info(si, offset);
> +	can_batch = swap_is_last_map(si, offset, nr, &has_cache);
> +	if (can_batch) {
> +		for (i = 0; i < nr; i++)
> +			WRITE_ONCE(si->swap_map[offset + i], SWAP_HAS_CACHE);
> +	}
> +	unlock_cluster_or_swap_info(si, ci);
> +
> +	if (!can_batch)
> +		goto fallback;

I'd avoid "can_batch" and just do:

ci = lock_cluster_or_swap_info(si, offset);
if (!swap_is_last_map(si, offset, nr, &has_cache)) {
	unlock_cluster_or_swap_info(si, ci);
	goto fallback;
}
for (i = 0; i < nr; i++)
	WRITE_ONCE(si->swap_map[offset + i], SWAP_HAS_CACHE);
unlock_cluster_or_swap_info(si, ci);

> +	if (!has_cache) {
> +		spin_lock(&si->lock);

I'm no expert on that code, but we might drop the cluster lock the take 
the swap_info lock and then retake the cluster lock. I assume there are 
no races we are worrying about here, right?

> +		swap_entry_range_free(si, entry, nr);
> +		spin_unlock(&si->lock);
> +	}
> +	return has_cache;
> +
> +fallback:
> +	for (i = 0; i  < nr; i++) {

One space too much before the "<".

> +		if (data_race(si->swap_map[offset + i])) {
> +			count = __swap_entry_free(si, swp_entry(type, offset + i));
> +			if (count == SWAP_HAS_CACHE)
> +				has_cache = true;
> +		} else {
> +			WARN_ON_ONCE(1);
> +		}
> +	}
> +	return has_cache;
> +}
> +

-- 
Cheers,

David / dhildenb

Re: [PATCH v2 2/2] mm: attempt to batch free swap entries for zap_pte_range()

[Barry Song]

On Wed, Aug 7, 2024 at 9:29 PM David Hildenbrand <david@redhat.com> wrote:
>
> >   mm/swapfile.c | 78 +++++++++++++++++++++++++++++++++++++++++++--------
> >   1 file changed, 67 insertions(+), 11 deletions(-)
> >
> > diff --git a/mm/swapfile.c b/mm/swapfile.c
> > index 35cb58373493..25c3f98fa8d5 100644
> > --- a/mm/swapfile.c
> > +++ b/mm/swapfile.c
> > @@ -156,6 +156,25 @@ static bool swap_is_has_cache(struct swap_info_struct *si,
> >       return true;
> >   }
> >
> > +static bool swap_is_last_map(struct swap_info_struct *si,
> > +                           unsigned long offset, int nr_pages,
> > +                           bool *has_cache)
>
> Please use double tabs for indenting parameters on 2nd line on
> new/changed code:
>
>                 unsigned long offset, int nr_pages, bool *has_cache)
>
> Results in less churn when renaming functions and we can frequently
> avoid some lines.

ack.

>
> > +{
> > +     unsigned char *map = si->swap_map + offset;
> > +     unsigned char *map_end = map + nr_pages;
> > +     bool cached = false;
> > +
> > +     do {
> > +             if ((*map & ~SWAP_HAS_CACHE) != 1)
> > +                     return false;
> > +             if (*map & SWAP_HAS_CACHE)
> > +                     cached = true;
> > +     } while (++map < map_end);
> > +
> > +     *has_cache = cached;
> > +     return true;
> > +}
> > +
> >   /*
> >    * returns number of pages in the folio that backs the swap entry. If positive,
> >    * the folio was reclaimed. If negative, the folio was not reclaimed. If 0, no
> > @@ -1469,6 +1488,53 @@ static unsigned char __swap_entry_free(struct swap_info_struct *si,
> >       return usage;
> >   }
> >
> > +static bool __swap_entries_free(struct swap_info_struct *si,
> > +                             swp_entry_t entry, int nr)
>
> Dito.

ack.

>
> > +{
> > +     unsigned long offset = swp_offset(entry);
> > +     unsigned int type = swp_type(entry);
> > +     struct swap_cluster_info *ci;
> > +     bool has_cache = false;
> > +     unsigned char count;
> > +     bool can_batch;
> > +     int i;
> > +
> > +     if (nr <= 1 || swap_count(data_race(si->swap_map[offset])) != 1)
> > +             goto fallback;
> > +     /* cross into another cluster */
> > +     if (nr > SWAPFILE_CLUSTER - offset % SWAPFILE_CLUSTER)
> > +             goto fallback;
> > +
> > +     ci = lock_cluster_or_swap_info(si, offset);
> > +     can_batch = swap_is_last_map(si, offset, nr, &has_cache);
> > +     if (can_batch) {
> > +             for (i = 0; i < nr; i++)
> > +                     WRITE_ONCE(si->swap_map[offset + i], SWAP_HAS_CACHE);
> > +     }
> > +     unlock_cluster_or_swap_info(si, ci);
> > +
> > +     if (!can_batch)
> > +             goto fallback;
>
> I'd avoid "can_batch" and just do:
>
> ci = lock_cluster_or_swap_info(si, offset);
> if (!swap_is_last_map(si, offset, nr, &has_cache)) {
>         unlock_cluster_or_swap_info(si, ci);
>         goto fallback;
> }
> for (i = 0; i < nr; i++)
>         WRITE_ONCE(si->swap_map[offset + i], SWAP_HAS_CACHE);
> unlock_cluster_or_swap_info(si, ci);

ack.

>
> > +     if (!has_cache) {
> > +             spin_lock(&si->lock);
>
> I'm no expert on that code, but we might drop the cluster lock the take
> the swap_info lock and then retake the cluster lock. I assume there are
> no races we are worrying about here, right?

I suppose so. Even the original single-entry code follows the same pattern:

static unsigned char __swap_entry_free(struct swap_info_struct *p,
       swp_entry_t entry)
{
         struct swap_cluster_info *ci;
         unsigned long offset = swp_offset(entry);
         unsigned char usage;

         ci = lock_cluster_or_swap_info(p, offset);
         usage = __swap_entry_free_locked(p, offset, 1);
         unlock_cluster_or_swap_info(p, ci);
         if (!usage)
                  free_swap_slot(entry);

         return usage;
}

I assume that once we mark them as SWAP_HAS_CACHE, no one else
will touch them except ourselves.

>
> > +             swap_entry_range_free(si, entry, nr);
> > +             spin_unlock(&si->lock);
> > +     }
> > +     return has_cache;
> > +
> > +fallback:
> > +     for (i = 0; i  < nr; i++) {
>
> One space too much before the "<".

ack.

>
> > +             if (data_race(si->swap_map[offset + i])) {
> > +                     count = __swap_entry_free(si, swp_entry(type, offset + i));
> > +                     if (count == SWAP_HAS_CACHE)
> > +                             has_cache = true;
> > +             } else {
> > +                     WARN_ON_ONCE(1);
> > +             }
> > +     }
> > +     return has_cache;
> > +}
> > +
>
> --
> Cheers,
>
> David / dhildenb
>

Thanks
Barry

Re: [PATCH v2 2/2] mm: attempt to batch free swap entries for zap_pte_range()

[David Hildenbrand]

>>
>>> +     if (!has_cache) {
>>> +             spin_lock(&si->lock);
>>
>> I'm no expert on that code, but we might drop the cluster lock the take
>> the swap_info lock and then retake the cluster lock. I assume there are
>> no races we are worrying about here, right?
> 
> I suppose so. Even the original single-entry code follows the same pattern:
> 
> static unsigned char __swap_entry_free(struct swap_info_struct *p,
>         swp_entry_t entry)
> {
>           struct swap_cluster_info *ci;
>           unsigned long offset = swp_offset(entry);
>           unsigned char usage;
> 
>           ci = lock_cluster_or_swap_info(p, offset);
>           usage = __swap_entry_free_locked(p, offset, 1);
>           unlock_cluster_or_swap_info(p, ci);
>           if (!usage)
>                    free_swap_slot(entry);
> 
>           return usage;
> }
> 
> I assume that once we mark them as SWAP_HAS_CACHE, no one else
> will touch them except ourselves.

That makes sense, thanks!

-- 
Cheers,

David / dhildenb

Re: [PATCH v2 2/2] mm: attempt to batch free swap entries for zap_pte_range()

[Kairui Song]

On Wed, Aug 7, 2024 at 4:25 PM Barry Song <21cnbao@gmail.com> wrote:
>
> From: Barry Song <v-songbaohua@oppo.com>
>
> Zhiguo reported that swap release could be a serious bottleneck
> during process exits[1]. With mTHP, we have the opportunity to
> batch free swaps.
> Thanks to the work of Chris and Kairui[2], I was able to achieve
> this optimization with minimal code changes by building on their
> efforts.
> If swap_count is 1, which is likely true as most anon memory are
> private, we can free all contiguous swap slots all together.
>
> Ran the below test program for measuring the bandwidth of munmap
> using zRAM and 64KiB mTHP:
>
>  #include <sys/mman.h>
>  #include <sys/time.h>
>  #include <stdlib.h>
>
>  unsigned long long tv_to_ms(struct timeval tv)
>  {
>         return tv.tv_sec * 1000 + tv.tv_usec / 1000;
>  }
>
>  main()
>  {
>         struct timeval tv_b, tv_e;
>         int i;
>  #define SIZE 1024*1024*1024
>         void *p = mmap(NULL, SIZE, PROT_READ | PROT_WRITE,
>                                 MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
>         if (!p) {
>                 perror("fail to get memory");
>                 exit(-1);
>         }
>
>         madvise(p, SIZE, MADV_HUGEPAGE);
>         memset(p, 0x11, SIZE); /* write to get mem */
>
>         madvise(p, SIZE, MADV_PAGEOUT);
>
>         gettimeofday(&tv_b, NULL);
>         munmap(p, SIZE);
>         gettimeofday(&tv_e, NULL);
>
>         printf("munmap in bandwidth: %ld bytes/ms\n",
>                         SIZE/(tv_to_ms(tv_e) - tv_to_ms(tv_b)));
>  }
>
> The result is as below (munmap bandwidth):
>                 mm-unstable  mm-unstable-with-patch
>    round1       21053761      63161283
>    round2       21053761      63161283
>    round3       21053761      63161283
>    round4       20648881      67108864
>    round5       20648881      67108864
>
> munmap bandwidth becomes 3X faster.

Hi Barry,

Thanks for the patch, I also noticed this could be optimized when
working on the batch freeing of mthp pages in the series you
mentioned, a very nice improvement.

>
> [1] https://lore.kernel.org/linux-mm/20240731133318.527-1-justinjiang@vivo.com/
> [2] https://lore.kernel.org/linux-mm/20240730-swap-allocator-v5-0-cb9c148b9297@kernel.org/
>
> Cc: Kairui Song <kasong@tencent.com>
> Cc: Chris Li <chrisl@kernel.org>
> Cc: "Huang, Ying" <ying.huang@intel.com>
> Cc: Hugh Dickins <hughd@google.com>
> Cc: Kalesh Singh <kaleshsingh@google.com>
> Cc: Ryan Roberts <ryan.roberts@arm.com>
> Cc: David Hildenbrand <david@redhat.com>
> Signed-off-by: Barry Song <v-songbaohua@oppo.com>
> ---
>  mm/swapfile.c | 78 +++++++++++++++++++++++++++++++++++++++++++--------
>  1 file changed, 67 insertions(+), 11 deletions(-)
>
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index 35cb58373493..25c3f98fa8d5 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -156,6 +156,25 @@ static bool swap_is_has_cache(struct swap_info_struct *si,
>         return true;
>  }
>
> +static bool swap_is_last_map(struct swap_info_struct *si,
> +                             unsigned long offset, int nr_pages,
> +                             bool *has_cache)
> +{
> +       unsigned char *map = si->swap_map + offset;
> +       unsigned char *map_end = map + nr_pages;
> +       bool cached = false;
> +
> +       do {
> +               if ((*map & ~SWAP_HAS_CACHE) != 1)
> +                       return false;

I haven't tried this yet, but looking at this if. If a mthp or thp was
split, and part of the slots are "1", rest of the slots are "HAS_CACHE
| 1", this will also return true, is this a problem?

These slots with "1" don't have an entry in the swap cache, so the
following reclaim in free_swap_and_cache_nr might not work as
expected, could they be stuck in HAS_CACHE state?

Re: [PATCH v2 2/2] mm: attempt to batch free swap entries for zap_pte_range()

[Barry Song]

On Thu, Aug 8, 2024 at 4:16 AM Kairui Song <ryncsn@gmail.com> wrote:
>
> On Wed, Aug 7, 2024 at 4:25 PM Barry Song <21cnbao@gmail.com> wrote:
> >
> > From: Barry Song <v-songbaohua@oppo.com>
> >
> > Zhiguo reported that swap release could be a serious bottleneck
> > during process exits[1]. With mTHP, we have the opportunity to
> > batch free swaps.
> > Thanks to the work of Chris and Kairui[2], I was able to achieve
> > this optimization with minimal code changes by building on their
> > efforts.
> > If swap_count is 1, which is likely true as most anon memory are
> > private, we can free all contiguous swap slots all together.
> >
> > Ran the below test program for measuring the bandwidth of munmap
> > using zRAM and 64KiB mTHP:
> >
> >  #include <sys/mman.h>
> >  #include <sys/time.h>
> >  #include <stdlib.h>
> >
> >  unsigned long long tv_to_ms(struct timeval tv)
> >  {
> >         return tv.tv_sec * 1000 + tv.tv_usec / 1000;
> >  }
> >
> >  main()
> >  {
> >         struct timeval tv_b, tv_e;
> >         int i;
> >  #define SIZE 1024*1024*1024
> >         void *p = mmap(NULL, SIZE, PROT_READ | PROT_WRITE,
> >                                 MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
> >         if (!p) {
> >                 perror("fail to get memory");
> >                 exit(-1);
> >         }
> >
> >         madvise(p, SIZE, MADV_HUGEPAGE);
> >         memset(p, 0x11, SIZE); /* write to get mem */
> >
> >         madvise(p, SIZE, MADV_PAGEOUT);
> >
> >         gettimeofday(&tv_b, NULL);
> >         munmap(p, SIZE);
> >         gettimeofday(&tv_e, NULL);
> >
> >         printf("munmap in bandwidth: %ld bytes/ms\n",
> >                         SIZE/(tv_to_ms(tv_e) - tv_to_ms(tv_b)));
> >  }
> >
> > The result is as below (munmap bandwidth):
> >                 mm-unstable  mm-unstable-with-patch
> >    round1       21053761      63161283
> >    round2       21053761      63161283
> >    round3       21053761      63161283
> >    round4       20648881      67108864
> >    round5       20648881      67108864
> >
> > munmap bandwidth becomes 3X faster.
>
> Hi Barry,
>
> Thanks for the patch, I also noticed this could be optimized when
> working on the batch freeing of mthp pages in the series you
> mentioned, a very nice improvement.
>
> >
> > [1] https://lore.kernel.org/linux-mm/20240731133318.527-1-justinjiang@vivo.com/
> > [2] https://lore.kernel.org/linux-mm/20240730-swap-allocator-v5-0-cb9c148b9297@kernel.org/
> >
> > Cc: Kairui Song <kasong@tencent.com>
> > Cc: Chris Li <chrisl@kernel.org>
> > Cc: "Huang, Ying" <ying.huang@intel.com>
> > Cc: Hugh Dickins <hughd@google.com>
> > Cc: Kalesh Singh <kaleshsingh@google.com>
> > Cc: Ryan Roberts <ryan.roberts@arm.com>
> > Cc: David Hildenbrand <david@redhat.com>
> > Signed-off-by: Barry Song <v-songbaohua@oppo.com>
> > ---
> >  mm/swapfile.c | 78 +++++++++++++++++++++++++++++++++++++++++++--------
> >  1 file changed, 67 insertions(+), 11 deletions(-)
> >
> > diff --git a/mm/swapfile.c b/mm/swapfile.c
> > index 35cb58373493..25c3f98fa8d5 100644
> > --- a/mm/swapfile.c
> > +++ b/mm/swapfile.c
> > @@ -156,6 +156,25 @@ static bool swap_is_has_cache(struct swap_info_struct *si,
> >         return true;
> >  }
> >
> > +static bool swap_is_last_map(struct swap_info_struct *si,
> > +                             unsigned long offset, int nr_pages,
> > +                             bool *has_cache)
> > +{
> > +       unsigned char *map = si->swap_map + offset;
> > +       unsigned char *map_end = map + nr_pages;
> > +       bool cached = false;
> > +
> > +       do {
> > +               if ((*map & ~SWAP_HAS_CACHE) != 1)
> > +                       return false;
>
> I haven't tried this yet, but looking at this if. If a mthp or thp was
> split, and part of the slots are "1", rest of the slots are "HAS_CACHE
> | 1", this will also return true, is this a problem?
>
> These slots with "1" don't have an entry in the swap cache, so the
> following reclaim in free_swap_and_cache_nr might not work as
> expected, could they be stuck in HAS_CACHE state?

good catch. Kairui, Thanks! In this case, I am leaking swap slots whose
count == 1.
The original non-batch code will still free those slots in non-batched mode
but my code will just write them to SWAP_HAS_CACHE.
this can be fixed by:

static bool swap_is_last_map(struct swap_info_struct *si,
                unsigned long offset, int nr_pages, bool *has_cache)
{
        unsigned char *map = si->swap_map + offset;
        unsigned char *map_end = map + nr_pages;
        unsigned char count = *map;

        if (swap_count(count) != 1)
                return false;

        do {
                if (*map != count)
                        return false;
        } while (++map < map_end);

        *has_cache = !!(count & SWAP_HAS_CACHE);
        return true;
}

Thanks
Barry