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Mon, 25 May 2026 05:23:17 -0700 (PDT) From: Hao Jia To: akpm@linux-foundation.org, tj@kernel.org, hannes@cmpxchg.org, shakeel.butt@linux.dev, mhocko@kernel.org, yosry@kernel.org, mkoutny@suse.com, nphamcs@gmail.com, chengming.zhou@linux.dev, muchun.song@linux.dev, roman.gushchin@linux.dev Cc: cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, Hao Jia Subject: [PATCH v2 3/4] mm/zswap: Add per-memcg stat for proactive writeback Date: Mon, 25 May 2026 20:22:41 +0800 Message-Id: <20260525122242.36127-4-jiahao.kernel@gmail.com> X-Mailer: git-send-email 2.39.2 (Apple Git-143) In-Reply-To: <20260525122242.36127-1-jiahao.kernel@gmail.com> References: <20260525122242.36127-1-jiahao.kernel@gmail.com> Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Hao Jia Currently, zswap writeback can be triggered by either the pool limit being hit or by the proactive writeback mechanism. However, the existing 'zswpwb' metric in memory.stat and /proc/vmstat counts all written back pages, making it difficult to distinguish between pages written back due to the pool limit and those written back proactively. Add a new statistic 'zswpwb_proactive' to memory.stat and /proc/vmstat. This counter tracks the number of pages written back due to proactive writeback. This allows users to better monitor and tune the proactive writeback mechanism. Signed-off-by: Hao Jia --- Documentation/admin-guide/cgroup-v2.rst | 4 +++ include/linux/vm_event_item.h | 1 + mm/memcontrol.c | 1 + mm/vmstat.c | 1 + mm/zswap.c | 41 ++++++++++++++++++------- 5 files changed, 37 insertions(+), 11 deletions(-) diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst index 6564abf0dec5..7d65aef83f7b 100644 --- a/Documentation/admin-guide/cgroup-v2.rst +++ b/Documentation/admin-guide/cgroup-v2.rst @@ -1748,6 +1748,10 @@ The following nested keys are defined. zswpwb Number of pages written from zswap to swap. + zswpwb_proactive + Number of pages written from zswap to swap by proactive + writeback. This is a subset of zswpwb. + zswap_incomp Number of incompressible pages currently stored in zswap without compression. These pages could not be compressed to diff --git a/include/linux/vm_event_item.h b/include/linux/vm_event_item.h index 03fe95f5a020..7a5bee0a20b6 100644 --- a/include/linux/vm_event_item.h +++ b/include/linux/vm_event_item.h @@ -138,6 +138,7 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT, ZSWPIN, ZSWPOUT, ZSWPWB, + ZSWPWB_PROACTIVE, #endif #ifdef CONFIG_X86 DIRECT_MAP_LEVEL2_SPLIT, diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 409c41359dc8..67de71b2a659 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -571,6 +571,7 @@ static const unsigned int memcg_vm_event_stat[] = { ZSWPIN, ZSWPOUT, ZSWPWB, + ZSWPWB_PROACTIVE, #endif #ifdef CONFIG_TRANSPARENT_HUGEPAGE THP_FAULT_ALLOC, diff --git a/mm/vmstat.c b/mm/vmstat.c index f534972f517d..66fd06d1bb01 100644 --- a/mm/vmstat.c +++ b/mm/vmstat.c @@ -1452,6 +1452,7 @@ const char * const vmstat_text[] = { [I(ZSWPIN)] = "zswpin", [I(ZSWPOUT)] = "zswpout", [I(ZSWPWB)] = "zswpwb", + [I(ZSWPWB_PROACTIVE)] = "zswpwb_proactive", #endif #ifdef CONFIG_X86 [I(DIRECT_MAP_LEVEL2_SPLIT)] = "direct_map_level2_splits", diff --git a/mm/zswap.c b/mm/zswap.c index 947507b9a185..78190631e2c4 100644 --- a/mm/zswap.c +++ b/mm/zswap.c @@ -160,6 +160,11 @@ struct zswap_pool { char tfm_name[CRYPTO_MAX_ALG_NAME]; }; +struct zswap_shrink_walk_arg { + bool proactive; + bool encountered_page_in_swapcache; +}; + /* Global LRU lists shared by all zswap pools. */ static struct list_lru zswap_list_lru; @@ -1042,7 +1047,8 @@ static bool zswap_decompress(struct zswap_entry *entry, struct folio *folio) * freed. */ static int zswap_writeback_entry(struct zswap_entry *entry, - swp_entry_t swpentry) + swp_entry_t swpentry, + bool proactive) { struct xarray *tree; pgoff_t offset = swp_offset(swpentry); @@ -1102,6 +1108,12 @@ static int zswap_writeback_entry(struct zswap_entry *entry, if (entry->objcg) count_objcg_events(entry->objcg, ZSWPWB, 1); + if (proactive) { + count_vm_event(ZSWPWB_PROACTIVE); + if (entry->objcg) + count_objcg_events(entry->objcg, ZSWPWB_PROACTIVE, 1); + } + zswap_entry_free(entry); /* folio is up to date */ @@ -1151,7 +1163,8 @@ static enum lru_status shrink_memcg_cb(struct list_head *item, struct list_lru_o void *arg) { struct zswap_entry *entry = container_of(item, struct zswap_entry, lru); - bool *encountered_page_in_swapcache = (bool *)arg; + struct zswap_shrink_walk_arg *walk_arg = arg; + bool proactive_wb = walk_arg && walk_arg->proactive; swp_entry_t swpentry; enum lru_status ret = LRU_REMOVED_RETRY; int writeback_result; @@ -1206,7 +1219,7 @@ static enum lru_status shrink_memcg_cb(struct list_head *item, struct list_lru_o */ spin_unlock(&l->lock); - writeback_result = zswap_writeback_entry(entry, swpentry); + writeback_result = zswap_writeback_entry(entry, swpentry, proactive_wb); if (writeback_result) { zswap_reject_reclaim_fail++; @@ -1217,9 +1230,9 @@ static enum lru_status shrink_memcg_cb(struct list_head *item, struct list_lru_o * into the warmer region. We should terminate shrinking (if we're in the dynamic * shrinker context). */ - if (writeback_result == -EEXIST && encountered_page_in_swapcache) { + if (writeback_result == -EEXIST && walk_arg) { ret = LRU_STOP; - *encountered_page_in_swapcache = true; + walk_arg->encountered_page_in_swapcache = true; } } else { zswap_written_back_pages++; @@ -1231,8 +1244,11 @@ static enum lru_status shrink_memcg_cb(struct list_head *item, struct list_lru_o static unsigned long zswap_shrinker_scan(struct shrinker *shrinker, struct shrink_control *sc) { + struct zswap_shrink_walk_arg walk_arg = { + .proactive = false, + .encountered_page_in_swapcache = false, + }; unsigned long shrink_ret; - bool encountered_page_in_swapcache = false; if (!zswap_shrinker_enabled || !mem_cgroup_zswap_writeback_enabled(sc->memcg)) { @@ -1241,9 +1257,9 @@ static unsigned long zswap_shrinker_scan(struct shrinker *shrinker, } shrink_ret = list_lru_shrink_walk(&zswap_list_lru, sc, &shrink_memcg_cb, - &encountered_page_in_swapcache); + &walk_arg); - if (encountered_page_in_swapcache) + if (walk_arg.encountered_page_in_swapcache) return SHRINK_STOP; return shrink_ret ? shrink_ret : SHRINK_STOP; @@ -1714,7 +1730,10 @@ static long zswap_proactive_shrink_memcg(struct mem_cgroup *memcg, return -ENOENT; for_each_node_state(nid, N_NORMAL_MEMORY) { - bool encountered_page_in_swapcache = false; + struct zswap_shrink_walk_arg walk_arg = { + .proactive = true, + .encountered_page_in_swapcache = false, + }; unsigned long nr_to_scan, nr_scanned = 0; /* @@ -1748,12 +1767,12 @@ static long zswap_proactive_shrink_memcg(struct mem_cgroup *memcg, nr_written += list_lru_walk_one(&zswap_list_lru, nid, memcg, &shrink_memcg_cb, - &encountered_page_in_swapcache, + &walk_arg, &nr_to_walk); if (nr_written >= nr_to_write) return nr_written; - if (encountered_page_in_swapcache) + if (walk_arg.encountered_page_in_swapcache) break; cond_resched(); -- 2.34.1