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From: Chengming Zhou In-Reply-To: <20240322001001.1562517-1-yosryahmed@google.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: ACFEA4000E X-Stat-Signature: scxn8hkkyrppd7mtjb7wfjwgke66fdo6 X-Rspam-User: X-HE-Tag: 1711075608-792632 X-HE-Meta: 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 Z34zxVJA 45LdG8286lMfIojgL3FtsR5x8twrIc7W14GTpdmvWdgTZVEiZFhZi3Xe5A3ViE/LEOXja13E5vOyCr4Fzf9x3zkOWuBEThxLR0uEtxYqM7sCHfnGih4cOTcY3XK0spGHrRJzm1tbnumqEEbFXvws8J5gsE2ZTaP8gILR2CGW4DenoQNs5YoGkptCe3w== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2024/3/22 08:10, Yosry Ahmed wrote: > nr_stored was introduced by commit b5ba474f3f51 ("zswap: shrink zswap > pool based on memory pressure") as a per zswap_pool counter of the > number of stored pages that are not same-filled pages. It is used in > zswap_shrinker_count() to scale the number of freeable compressed pages > by the compression ratio. That is, to reduce the amount of writeback > from zswap with higher compression ratios as the ROI from IO diminishes. > > Later on, commit bf9b7df23cb3 ("mm/zswap: global lru and shrinker shared > by all zswap_pools") made the shrinker global (not per zswap_pool), and > replaced nr_stored with nr_zswap_stored (initially introduced as > zswap.nr_stored), which is now a global counter. > > The counter is now awfully close to zswap_stored_pages. The only > difference is that the latter also includes same-filled pages. Also, > when memcgs are enabled, we use memcg_page_state(memcg, MEMCG_ZSWAPPED), > which includes same-filled pages anyway (i.e. equivalent to > zswap_stored_pages). > > Use zswap_stored_pages instead in zswap_shrinker_count() to keep things > consistent whether memcgs are enabled or not, and add a comment about > the number of freeable pages possibly being scaled down more than it > should if we have lots of same-filled pages (i.e. inflated compression > ratio). > > Remove nr_zswap_stored and one atomic operation in the store and free > paths. > > Signed-off-by: Yosry Ahmed > Reviewed-by: Nhat Pham Reviewed-by: Chengming Zhou Thanks. > --- > mm/zswap.c | 11 ++++++----- > 1 file changed, 6 insertions(+), 5 deletions(-) > > diff --git a/mm/zswap.c b/mm/zswap.c > index b31c977f53e9c..1a79f99606cef 100644 > --- a/mm/zswap.c > +++ b/mm/zswap.c > @@ -181,8 +181,6 @@ struct zswap_pool { > > /* Global LRU lists shared by all zswap pools. */ > static struct list_lru zswap_list_lru; > -/* counter of pages stored in all zswap pools. */ > -static atomic_t zswap_nr_stored = ATOMIC_INIT(0); > > /* The lock protects zswap_next_shrink updates. */ > static DEFINE_SPINLOCK(zswap_shrink_lock); > @@ -885,7 +883,6 @@ static void zswap_entry_free(struct zswap_entry *entry) > else { > zswap_lru_del(&zswap_list_lru, entry); > zpool_free(zswap_find_zpool(entry), entry->handle); > - atomic_dec(&zswap_nr_stored); > zswap_pool_put(entry->pool); > } > if (entry->objcg) { > @@ -1310,7 +1307,7 @@ static unsigned long zswap_shrinker_count(struct shrinker *shrinker, > #else > /* use pool stats instead of memcg stats */ > nr_backing = zswap_total_pages(); > - nr_stored = atomic_read(&zswap_nr_stored); > + nr_stored = atomic_read(&zswap_stored_pages); > #endif > > if (!nr_stored) > @@ -1330,6 +1327,11 @@ 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); > } > @@ -1575,7 +1577,6 @@ bool zswap_store(struct folio *folio) > if (entry->length) { > INIT_LIST_HEAD(&entry->lru); > zswap_lru_add(&zswap_list_lru, entry); > - atomic_inc(&zswap_nr_stored); > } > spin_unlock(&tree->lock); >