Commit 20a5532f authored by Usama Arif's avatar Usama Arif Committed by Andrew Morton
Browse files

mm: remove code to handle same filled pages 

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.

Link: https://lkml.kernel.org/r/20240823190545.979059-3-usamaarif642@gmail.com


Signed-off-by: default avatarUsama Arif <usamaarif642@gmail.com>
Reviewed-by: default avatarChengming Zhou <chengming.zhou@linux.dev>
Acked-by: default avatarYosry Ahmed <yosryahmed@google.com>
Reviewed-by: default avatarNhat Pham <nphamcs@gmail.com>
Acked-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
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: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 0ca0c24e

mm/zswap.c

+8 −77
Original line number Diff line number Diff line
@@ -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;

	};

	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);

	}

	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);

put_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);



	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;

}