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Message-ID: <0e17c634-842b-40f6-b3bd-e4b98ed1dc8f@linux.dev>
Date: Fri, 14 Jun 2024 20:07:25 +0800
From: Chengming Zhou <chengming.zhou@...ux.dev>
To: Usama Arif <usamaarif642@...il.com>, akpm@...ux-foundation.org
Cc: hannes@...xchg.org, shakeel.butt@...ux.dev, david@...hat.com,
ying.huang@...el.com, hughd@...gle.com, willy@...radead.org,
yosryahmed@...gle.com, nphamcs@...il.com, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, kernel-team@...a.com
Subject: Re: [PATCH v5 2/2] mm: remove code to handle same filled pages
On 2024/6/14 18:07, Usama Arif wrote:
> 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.
>
> Signed-off-by: Usama Arif <usamaarif642@...il.com>
Looks good to me, thanks.
Reviewed-by: Chengming Zhou <chengming.zhou@...ux.dev>
> ---
> mm/zswap.c | 86 +++++-------------------------------------------------
> 1 file changed, 8 insertions(+), 78 deletions(-)
>
> diff --git a/mm/zswap.c b/mm/zswap.c
> index a546c01602aa..e25a6808c2ed 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
> @@ -188,11 +186,9 @@ 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.
> * pool - the zswap_pool the entry's data is in
> * handle - zpool allocation handle that stores the compressed page data
> - * value - value of the same-value filled pages which have same content
> * objcg - the obj_cgroup that the compressed memory is charged to
> * lru - handle to the pool's lru used to evict pages.
> */
> @@ -200,10 +196,7 @@ struct zswap_entry {
> swp_entry_t swpentry;
> unsigned int length;
> struct zswap_pool *pool;
> - union {
> - unsigned long handle;
> - unsigned long value;
> - };
> + unsigned long handle;
> struct obj_cgroup *objcg;
> struct list_head lru;
> };
> @@ -820,13 +813,9 @@ static struct zpool *zswap_find_zpool(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(zswap_find_zpool(entry), entry->handle);
> - zswap_pool_put(entry->pool);
> - }
> + zswap_lru_del(&zswap_list_lru, entry);
> + zpool_free(zswap_find_zpool(entry), entry->handle);
> + zswap_pool_put(entry->pool);
> if (entry->objcg) {
> obj_cgroup_uncharge_zswap(entry->objcg, entry->length);
> obj_cgroup_put(entry->objcg);
> @@ -1268,11 +1257,6 @@ 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);
> }
> @@ -1376,42 +1360,6 @@ 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
> **********************************/
> @@ -1423,7 +1371,6 @@ 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));
> @@ -1456,13 +1403,6 @@ 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)
> @@ -1480,7 +1420,6 @@ bool zswap_store(struct folio *folio)
> if (!zswap_compress(folio, entry))
> goto put_pool;
>
> -store_entry:
> entry->swpentry = swp;
> entry->objcg = objcg;
>
> @@ -1528,13 +1467,9 @@ bool zswap_store(struct folio *folio)
> return true;
>
> store_failed:
> - if (!entry->length)
> - atomic_dec(&zswap_same_filled_pages);
> - else {
> - zpool_free(zswap_find_zpool(entry), entry->handle);
> + zpool_free(zswap_find_zpool(entry), entry->handle);
> put_pool:
> - zswap_pool_put(entry->pool);
> - }
> + zswap_pool_put(entry->pool);
> freepage:
> zswap_entry_cache_free(entry);
> reject:
> @@ -1597,10 +1532,7 @@ 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)
> @@ -1703,8 +1635,6 @@ 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;
> }
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