[RESEND v8 0/2] mm: store zero pages to be swapped out in a bitmap

[RESEND v8 0/2] mm: store zero pages to be swapped out in a bitmap

[Usama Arif]

Resending it, as the CC had "Huang, Ying" in one of the initial patches,
and it was rejected by git send-email because of the "," in name.

The original series [1] was almost merged, but was dropped
due to a last minute bug [2]. Resending this with the fix for it,
by handling zeromap in the same way as swap_map and cluster_info in
enable_swap_info, holding swapon_mutex and si->lock, hence avoiding
a race condition between swapon and any point where the lock is held. 
This is the safest way.

The series had already been reviewed and acked by all maintainers.

Hoping that this attempt goes better than the initial one :)

This patchseries is based on mm-unstable from today:
4926e8348e10 - (akpm/mm-unstable) mm: optimization on page allocation when CMA enabled

[1] https://lore.kernel.org/all/20240627105730.3110705-1-usamaarif642@gmail.com/
[2] https://lore.kernel.org/all/202407101031.c6c3c651-lkp@intel.com/

Usama Arif (2):
  mm: store zero pages to be swapped out in a bitmap
  mm: remove code to handle same filled pages

 include/linux/swap.h |   1 +
 mm/page_io.c         | 118 ++++++++++++++++++++++++++++++++++++++++++-
 mm/swapfile.c        |  38 ++++++++++++--
 mm/zswap.c           |  85 +++----------------------------
 4 files changed, 159 insertions(+), 83 deletions(-)

-- 
2.43.5

[RESEND v8 1/2] mm: store zero pages to be swapped out in a bitmap

[Usama Arif]

Approximately 10-20% of pages to be swapped out are zero pages [1].
Rather than reading/writing these pages to flash resulting
in increased I/O and flash wear, a bitmap can be used to mark these
pages as zero at write time, and the pages can be filled at
read time if the bit corresponding to the page is set.
With this patch, NVMe writes in Meta server fleet decreased
by almost 10% with conventional swap setup (zswap disabled).

[1] https://lore.kernel.org/all/20171018104832epcms5p1b2232e2236258de3d03d1344dde9fce0@epcms5p1/

Signed-off-by: Usama Arif <usamaarif642@gmail.com>
Reviewed-by: Chengming Zhou <chengming.zhou@linux.dev>
Reviewed-by: Yosry Ahmed <yosryahmed@google.com>
Reviewed-by: Nhat Pham <nphamcs@gmail.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Usama Arif <usamaarif642@gmail.com>
Cc: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
---
 include/linux/swap.h |   1 +
 mm/page_io.c         | 118 ++++++++++++++++++++++++++++++++++++++++++-
 mm/swapfile.c        |  38 ++++++++++++--
 3 files changed, 151 insertions(+), 6 deletions(-)

diff --git a/include/linux/swap.h b/include/linux/swap.h
index 248db1dd7812..ca533b478c21 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -296,6 +296,7 @@ struct swap_info_struct {
 	signed char	type;		/* strange name for an index */
 	unsigned int	max;		/* extent of the swap_map */
 	unsigned char *swap_map;	/* vmalloc'ed array of usage counts */
+	unsigned long *zeromap;		/* kvmalloc'ed bitmap to track zero pages */
 	struct swap_cluster_info *cluster_info; /* cluster info. Only for SSD */
 	struct list_head free_clusters; /* free clusters list */
 	struct list_head full_clusters; /* full clusters list */
diff --git a/mm/page_io.c b/mm/page_io.c
index a00e2f615118..b6f1519d63b0 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -172,6 +172,80 @@ int generic_swapfile_activate(struct swap_info_struct *sis,
 	goto out;
 }
 
+static bool is_folio_zero_filled(struct folio *folio)
+{
+	unsigned int pos, last_pos;
+	unsigned long *data;
+	unsigned int i;
+
+	last_pos = PAGE_SIZE / sizeof(*data) - 1;
+	for (i = 0; i < folio_nr_pages(folio); i++) {
+		data = kmap_local_folio(folio, i * PAGE_SIZE);
+		/*
+		 * Check last word first, incase the page is zero-filled at
+		 * the start and has non-zero data at the end, which is common
+		 * in real-world workloads.
+		 */
+		if (data[last_pos]) {
+			kunmap_local(data);
+			return false;
+		}
+		for (pos = 0; pos < last_pos; pos++) {
+			if (data[pos]) {
+				kunmap_local(data);
+				return false;
+			}
+		}
+		kunmap_local(data);
+	}
+
+	return true;
+}
+
+static void swap_zeromap_folio_set(struct folio *folio)
+{
+	struct swap_info_struct *sis = swp_swap_info(folio->swap);
+	swp_entry_t entry;
+	unsigned int i;
+
+	for (i = 0; i < folio_nr_pages(folio); i++) {
+		entry = page_swap_entry(folio_page(folio, i));
+		set_bit(swp_offset(entry), sis->zeromap);
+	}
+}
+
+static void swap_zeromap_folio_clear(struct folio *folio)
+{
+	struct swap_info_struct *sis = swp_swap_info(folio->swap);
+	swp_entry_t entry;
+	unsigned int i;
+
+	for (i = 0; i < folio_nr_pages(folio); i++) {
+		entry = page_swap_entry(folio_page(folio, i));
+		clear_bit(swp_offset(entry), sis->zeromap);
+	}
+}
+
+/*
+ * Return the index of the first subpage which is not zero-filled
+ * according to swap_info_struct->zeromap.
+ * If all pages are zero-filled according to zeromap, it will return
+ * folio_nr_pages(folio).
+ */
+static unsigned int swap_zeromap_folio_test(struct folio *folio)
+{
+	struct swap_info_struct *sis = swp_swap_info(folio->swap);
+	swp_entry_t entry;
+	unsigned int i;
+
+	for (i = 0; i < folio_nr_pages(folio); i++) {
+		entry = page_swap_entry(folio_page(folio, i));
+		if (!test_bit(swp_offset(entry), sis->zeromap))
+			return i;
+	}
+	return i;
+}
+
 /*
  * We may have stale swap cache pages in memory: notice
  * them here and get rid of the unnecessary final write.
@@ -195,6 +269,25 @@ int swap_writepage(struct page *page, struct writeback_control *wbc)
 		folio_unlock(folio);
 		return ret;
 	}
+
+	/*
+	 * Use a bitmap (zeromap) to avoid doing IO for zero-filled pages.
+	 * The bits in zeromap are protected by the locked swapcache folio
+	 * and atomic updates are used to protect against read-modify-write
+	 * corruption due to other zero swap entries seeing concurrent updates.
+	 */
+	if (is_folio_zero_filled(folio)) {
+		swap_zeromap_folio_set(folio);
+		folio_unlock(folio);
+		return 0;
+	} else {
+		/*
+		 * Clear bits this folio occupies in the zeromap to prevent
+		 * zero data being read in from any previous zero writes that
+		 * occupied the same swap entries.
+		 */
+		swap_zeromap_folio_clear(folio);
+	}
 	if (zswap_store(folio)) {
 		folio_unlock(folio);
 		return 0;
@@ -427,6 +520,26 @@ static void sio_read_complete(struct kiocb *iocb, long ret)
 	mempool_free(sio, sio_pool);
 }
 
+static bool swap_read_folio_zeromap(struct folio *folio)
+{
+	unsigned int idx = swap_zeromap_folio_test(folio);
+
+	if (idx == 0)
+		return false;
+
+	/*
+	 * Swapping in a large folio that is partially in the zeromap is not
+	 * currently handled. Return true without marking the folio uptodate so
+	 * that an IO error is emitted (e.g. do_swap_page() will sigbus).
+	 */
+	if (WARN_ON_ONCE(idx < folio_nr_pages(folio)))
+		return true;
+
+	folio_zero_range(folio, 0, folio_size(folio));
+	folio_mark_uptodate(folio);
+	return true;
+}
+
 static void swap_read_folio_fs(struct folio *folio, struct swap_iocb **plug)
 {
 	struct swap_info_struct *sis = swp_swap_info(folio->swap);
@@ -517,7 +630,10 @@ void swap_read_folio(struct folio *folio, struct swap_iocb **plug)
 	}
 	delayacct_swapin_start();
 
-	if (zswap_load(folio)) {
+	if (swap_read_folio_zeromap(folio)) {
+		folio_unlock(folio);
+		goto finish;
+	} else if (zswap_load(folio)) {
 		folio_unlock(folio);
 		goto finish;
 	}
diff --git a/mm/swapfile.c b/mm/swapfile.c
index aff73a3d0ead..1cfb7c63cdcc 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -940,6 +940,14 @@ static void swap_range_free(struct swap_info_struct *si, unsigned long offset,
 	unsigned long begin = offset;
 	unsigned long end = offset + nr_entries - 1;
 	void (*swap_slot_free_notify)(struct block_device *, unsigned long);
+	unsigned int i;
+
+	/*
+	 * Use atomic clear_bit operations only on zeromap instead of non-atomic
+	 * bitmap_clear to prevent adjacent bits corruption due to simultaneous writes.
+	 */
+	for (i = 0; i < nr_entries; i++)
+		clear_bit(offset + i, si->zeromap);
 
 	if (offset < si->lowest_bit)
 		si->lowest_bit = offset;
@@ -2607,7 +2615,8 @@ static int swap_node(struct swap_info_struct *si)
 
 static void setup_swap_info(struct swap_info_struct *si, int prio,
 			    unsigned char *swap_map,
-			    struct swap_cluster_info *cluster_info)
+			    struct swap_cluster_info *cluster_info,
+			    unsigned long *zeromap)
 {
 	int i;
 
@@ -2632,6 +2641,7 @@ static void setup_swap_info(struct swap_info_struct *si, int prio,
 	}
 	si->swap_map = swap_map;
 	si->cluster_info = cluster_info;
+	si->zeromap = zeromap;
 }
 
 static void _enable_swap_info(struct swap_info_struct *si)
@@ -2660,11 +2670,12 @@ static void _enable_swap_info(struct swap_info_struct *si)
 
 static void enable_swap_info(struct swap_info_struct *si, int prio,
 				unsigned char *swap_map,
-				struct swap_cluster_info *cluster_info)
+				struct swap_cluster_info *cluster_info,
+				unsigned long *zeromap)
 {
 	spin_lock(&swap_lock);
 	spin_lock(&si->lock);
-	setup_swap_info(si, prio, swap_map, cluster_info);
+	setup_swap_info(si, prio, swap_map, cluster_info, zeromap);
 	spin_unlock(&si->lock);
 	spin_unlock(&swap_lock);
 	/*
@@ -2682,7 +2693,7 @@ static void reinsert_swap_info(struct swap_info_struct *si)
 {
 	spin_lock(&swap_lock);
 	spin_lock(&si->lock);
-	setup_swap_info(si, si->prio, si->swap_map, si->cluster_info);
+	setup_swap_info(si, si->prio, si->swap_map, si->cluster_info, si->zeromap);
 	_enable_swap_info(si);
 	spin_unlock(&si->lock);
 	spin_unlock(&swap_lock);
@@ -2707,6 +2718,7 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
 {
 	struct swap_info_struct *p = NULL;
 	unsigned char *swap_map;
+	unsigned long *zeromap;
 	struct swap_cluster_info *cluster_info;
 	struct file *swap_file, *victim;
 	struct address_space *mapping;
@@ -2829,6 +2841,8 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
 	p->max = 0;
 	swap_map = p->swap_map;
 	p->swap_map = NULL;
+	zeromap = p->zeromap;
+	p->zeromap = NULL;
 	cluster_info = p->cluster_info;
 	p->cluster_info = NULL;
 	spin_unlock(&p->lock);
@@ -2841,6 +2855,7 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
 	free_percpu(p->cluster_next_cpu);
 	p->cluster_next_cpu = NULL;
 	vfree(swap_map);
+	kvfree(zeromap);
 	kvfree(cluster_info);
 	/* Destroy swap account information */
 	swap_cgroup_swapoff(p->type);
@@ -3338,6 +3353,7 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
 	sector_t span;
 	unsigned long maxpages;
 	unsigned char *swap_map = NULL;
+	unsigned long *zeromap = NULL;
 	struct swap_cluster_info *cluster_info = NULL;
 	struct page *page = NULL;
 	struct inode *inode = NULL;
@@ -3428,6 +3444,17 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
 		goto bad_swap_unlock_inode;
 	}
 
+	/*
+	 * Use kvmalloc_array instead of bitmap_zalloc as the allocation order might
+	 * be above MAX_PAGE_ORDER incase of a large swap file.
+	 */
+	zeromap = kvmalloc_array(BITS_TO_LONGS(maxpages), sizeof(long),
+				    GFP_KERNEL | __GFP_ZERO);
+	if (!zeromap) {
+		error = -ENOMEM;
+		goto bad_swap_unlock_inode;
+	}
+
 	if (si->bdev && bdev_stable_writes(si->bdev))
 		si->flags |= SWP_STABLE_WRITES;
 
@@ -3503,7 +3530,7 @@ 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(si, prio, swap_map, cluster_info);
+	enable_swap_info(si, prio, swap_map, cluster_info, zeromap);
 
 	pr_info("Adding %uk swap on %s.  Priority:%d extents:%d across:%lluk %s%s%s%s\n",
 		K(si->pages), name->name, si->prio, nr_extents,
@@ -3538,6 +3565,7 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
 	si->flags = 0;
 	spin_unlock(&swap_lock);
 	vfree(swap_map);
+	kvfree(zeromap);
 	kvfree(cluster_info);
 	if (inced_nr_rotate_swap)
 		atomic_dec(&nr_rotate_swap);
-- 
2.43.5

Re: [RESEND v8 1/2] mm: store zero pages to be swapped out in a bitmap

[Christophe JAILLET]

Le 23/08/2024 à 21:04, Usama Arif a écrit :
> Approximately 10-20% of pages to be swapped out are zero pages [1].
> Rather than reading/writing these pages to flash resulting
> in increased I/O and flash wear, a bitmap can be used to mark these
> pages as zero at write time, and the pages can be filled at
> read time if the bit corresponding to the page is set.
> With this patch, NVMe writes in Meta server fleet decreased
> by almost 10% with conventional swap setup (zswap disabled).
> 
> [1] https://lore.kernel.org/all/20171018104832epcms5p1b2232e2236258de3d03d1344dde9fce0@epcms5p1/
> 

...

> @@ -3428,6 +3444,17 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
>   		goto bad_swap_unlock_inode;
>   	}
>   
> +	/*
> +	 * Use kvmalloc_array instead of bitmap_zalloc as the allocation order might
> +	 * be above MAX_PAGE_ORDER incase of a large swap file.
> +	 */
> +	zeromap = kvmalloc_array(BITS_TO_LONGS(maxpages), sizeof(long),
> +				    GFP_KERNEL | __GFP_ZERO);

Nitpick: kvcalloc() maybe, to be slightly less verbose?

> +	if (!zeromap) {
> +		error = -ENOMEM;
> +		goto bad_swap_unlock_inode;
> +	}
> +
>   	if (si->bdev && bdev_stable_writes(si->bdev))
>   		si->flags |= SWP_STABLE_WRITES;
>   

...

CJ

Re: [RESEND v8 1/2] mm: store zero pages to be swapped out in a bitmap

[Usama Arif]

On 24/08/2024 02:55, Christophe JAILLET wrote:
> Le 23/08/2024 à 21:04, Usama Arif a écrit :
>> Approximately 10-20% of pages to be swapped out are zero pages [1].
>> Rather than reading/writing these pages to flash resulting
>> in increased I/O and flash wear, a bitmap can be used to mark these
>> pages as zero at write time, and the pages can be filled at
>> read time if the bit corresponding to the page is set.
>> With this patch, NVMe writes in Meta server fleet decreased
>> by almost 10% with conventional swap setup (zswap disabled).
>>
>> [1] https://lore.kernel.org/all/20171018104832epcms5p1b2232e2236258de3d03d1344dde9fce0@epcms5p1/
>>
> 
> ...
> 
>> @@ -3428,6 +3444,17 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
>>           goto bad_swap_unlock_inode;
>>       }
>>   +    /*
>> +     * Use kvmalloc_array instead of bitmap_zalloc as the allocation order might
>> +     * be above MAX_PAGE_ORDER incase of a large swap file.
>> +     */
>> +    zeromap = kvmalloc_array(BITS_TO_LONGS(maxpages), sizeof(long),
>> +                    GFP_KERNEL | __GFP_ZERO);
> 
> Nitpick: kvcalloc() maybe, to be slightly less verbose?
> 

There was quite a long discussion [1] on this in v5 of the series, and we settled no kvmalloc_array in the end. I think best to leave it as it is at kvmalloc_array.

Thanks

[1] https://lore.kernel.org/all/159061bc-27b5-4127-a85d-223bed0ddfd5@gmail.com/

[RESEND v8 2/2] mm: remove code to handle same filled pages

[Usama Arif]

With an earlier commit to handle zero-filled pages in swap directly,
and with only 1% of the same-filled pages being non-zero, zswap no
longer needs to handle same-filled pages and can just work on compressed
pages.

Reviewed-by: Chengming Zhou <chengming.zhou@linux.dev>
Acked-by: Yosry Ahmed <yosryahmed@google.com>
Reviewed-by: Nhat Pham <nphamcs@gmail.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Usama Arif <usamaarif642@gmail.com>
---
 mm/zswap.c | 85 +++++-------------------------------------------------
 1 file changed, 8 insertions(+), 77 deletions(-)

diff --git a/mm/zswap.c b/mm/zswap.c
index df66ab102d27..449914ea9919 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -44,8 +44,6 @@
 **********************************/
 /* The number of compressed pages currently stored in zswap */
 atomic_t zswap_stored_pages = ATOMIC_INIT(0);
-/* The number of same-value filled pages currently stored in zswap */
-static atomic_t zswap_same_filled_pages = ATOMIC_INIT(0);
 
 /*
  * The statistics below are not protected from concurrent access for
@@ -185,8 +183,7 @@ static struct shrinker *zswap_shrinker;
  *
  * swpentry - associated swap entry, the offset indexes into the red-black tree
  * length - the length in bytes of the compressed page data.  Needed during
- *          decompression. For a same value filled page length is 0, and both
- *          pool and lru are invalid and must be ignored.
+ *          decompression.
  * referenced - true if the entry recently entered the zswap pool. Unset by the
  *              writeback logic. The entry is only reclaimed by the writeback
  *              logic if referenced is unset. See comments in the shrinker
@@ -202,10 +199,7 @@ struct zswap_entry {
 	unsigned int length;
 	bool referenced;
 	struct zswap_pool *pool;
-	union {
-		unsigned long handle;
-		unsigned long value;
-	};
+	unsigned long handle;
 	struct obj_cgroup *objcg;
 	struct list_head lru;
 };
@@ -801,13 +795,9 @@ static void zswap_entry_cache_free(struct zswap_entry *entry)
  */
 static void zswap_entry_free(struct zswap_entry *entry)
 {
-	if (!entry->length)
-		atomic_dec(&zswap_same_filled_pages);
-	else {
-		zswap_lru_del(&zswap_list_lru, entry);
-		zpool_free(entry->pool->zpool, entry->handle);
-		zswap_pool_put(entry->pool);
-	}
+	zswap_lru_del(&zswap_list_lru, entry);
+	zpool_free(entry->pool->zpool, entry->handle);
+	zswap_pool_put(entry->pool);
 	if (entry->objcg) {
 		obj_cgroup_uncharge_zswap(entry->objcg, entry->length);
 		obj_cgroup_put(entry->objcg);
@@ -1277,11 +1267,6 @@ static unsigned long zswap_shrinker_count(struct shrinker *shrinker,
 	 * This ensures that the better zswap compresses memory, the fewer
 	 * pages we will evict to swap (as it will otherwise incur IO for
 	 * relatively small memory saving).
-	 *
-	 * The memory saving factor calculated here takes same-filled pages into
-	 * account, but those are not freeable since they almost occupy no
-	 * space. Hence, we may scale nr_freeable down a little bit more than we
-	 * should if we have a lot of same-filled pages.
 	 */
 	return mult_frac(nr_freeable, nr_backing, nr_stored);
 }
@@ -1416,42 +1401,6 @@ static void shrink_worker(struct work_struct *w)
 	} while (zswap_total_pages() > thr);
 }
 
-/*********************************
-* same-filled functions
-**********************************/
-static bool zswap_is_folio_same_filled(struct folio *folio, unsigned long *value)
-{
-	unsigned long *data;
-	unsigned long val;
-	unsigned int pos, last_pos = PAGE_SIZE / sizeof(*data) - 1;
-	bool ret = false;
-
-	data = kmap_local_folio(folio, 0);
-	val = data[0];
-
-	if (val != data[last_pos])
-		goto out;
-
-	for (pos = 1; pos < last_pos; pos++) {
-		if (val != data[pos])
-			goto out;
-	}
-
-	*value = val;
-	ret = true;
-out:
-	kunmap_local(data);
-	return ret;
-}
-
-static void zswap_fill_folio(struct folio *folio, unsigned long value)
-{
-	unsigned long *data = kmap_local_folio(folio, 0);
-
-	memset_l(data, value, PAGE_SIZE / sizeof(unsigned long));
-	kunmap_local(data);
-}
-
 /*********************************
 * main API
 **********************************/
@@ -1463,7 +1412,6 @@ bool zswap_store(struct folio *folio)
 	struct zswap_entry *entry, *old;
 	struct obj_cgroup *objcg = NULL;
 	struct mem_cgroup *memcg = NULL;
-	unsigned long value;
 
 	VM_WARN_ON_ONCE(!folio_test_locked(folio));
 	VM_WARN_ON_ONCE(!folio_test_swapcache(folio));
@@ -1496,13 +1444,6 @@ bool zswap_store(struct folio *folio)
 		goto reject;
 	}
 
-	if (zswap_is_folio_same_filled(folio, &value)) {
-		entry->length = 0;
-		entry->value = value;
-		atomic_inc(&zswap_same_filled_pages);
-		goto store_entry;
-	}
-
 	/* if entry is successfully added, it keeps the reference */
 	entry->pool = zswap_pool_current_get();
 	if (!entry->pool)
@@ -1520,7 +1461,6 @@ bool zswap_store(struct folio *folio)
 	if (!zswap_compress(folio, entry))
 		goto put_pool;
 
-store_entry:
 	entry->swpentry = swp;
 	entry->objcg = objcg;
 	entry->referenced = true;
@@ -1569,13 +1509,9 @@ bool zswap_store(struct folio *folio)
 	return true;
 
 store_failed:
-	if (!entry->length)
-		atomic_dec(&zswap_same_filled_pages);
-	else {
-		zpool_free(entry->pool->zpool, entry->handle);
+	zpool_free(entry->pool->zpool, entry->handle);
 put_pool:
-		zswap_pool_put(entry->pool);
-	}
+	zswap_pool_put(entry->pool);
 freepage:
 	zswap_entry_cache_free(entry);
 reject:
@@ -1638,10 +1574,7 @@ bool zswap_load(struct folio *folio)
 	if (!entry)
 		return false;
 
-	if (entry->length)
-		zswap_decompress(entry, folio);
-	else
-		zswap_fill_folio(folio, entry->value);
+	zswap_decompress(entry, folio);
 
 	count_vm_event(ZSWPIN);
 	if (entry->objcg)
@@ -1744,8 +1677,6 @@ static int zswap_debugfs_init(void)
 			    zswap_debugfs_root, NULL, &total_size_fops);
 	debugfs_create_atomic_t("stored_pages", 0444,
 				zswap_debugfs_root, &zswap_stored_pages);
-	debugfs_create_atomic_t("same_filled_pages", 0444,
-				zswap_debugfs_root, &zswap_same_filled_pages);
 
 	return 0;
 }
-- 
2.43.5

Re: [RESEND v8 0/2] mm: store zero pages to be swapped out in a bitmap

[Andrew Morton]

On Fri, 23 Aug 2024 20:04:38 +0100 Usama Arif <usamaarif642@gmail.com> wrote:

> Resending it, as the CC had "Huang, Ying" in one of the initial patches,
> and it was rejected by git send-email because of the "," in name.
> 
> The original series [1] was almost merged, but was dropped
> due to a last minute bug [2]. Resending this with the fix for it,
> by handling zeromap in the same way as swap_map and cluster_info in
> enable_swap_info, holding swapon_mutex and si->lock, hence avoiding
> a race condition between swapon and any point where the lock is held. 
> This is the safest way.
> 
> The series had already been reviewed and acked by all maintainers.
> 
> Hoping that this attempt goes better than the initial one :)

Yup ;)

We're missing the [0/n] words here.  I pasted the text from the v1
series.  Please check that it remains the truth, the whole truth and
nothing but the truth.

Re: [RESEND v8 0/2] mm: store zero pages to be swapped out in a bitmap

[Usama Arif]

On 24/08/2024 01:06, Andrew Morton wrote:
> On Fri, 23 Aug 2024 20:04:38 +0100 Usama Arif <usamaarif642@gmail.com> wrote:
> 
>> Resending it, as the CC had "Huang, Ying" in one of the initial patches,
>> and it was rejected by git send-email because of the "," in name.
>>
>> The original series [1] was almost merged, but was dropped
>> due to a last minute bug [2]. Resending this with the fix for it,
>> by handling zeromap in the same way as swap_map and cluster_info in
>> enable_swap_info, holding swapon_mutex and si->lock, hence avoiding
>> a race condition between swapon and any point where the lock is held. 
>> This is the safest way.
>>
>> The series had already been reviewed and acked by all maintainers.
>>
>> Hoping that this attempt goes better than the initial one :)
> 
> Yup ;)
> 
> We're missing the [0/n] words here.  I pasted the text from the v1
> series.  Please check that it remains the truth, the whole truth and
> nothing but the truth.

Yes, Thanks! The cover letter remains the same.