From 2d4d2b1cfb85cc07f6d5619acb882d8b11e55cf4 Mon Sep 17 00:00:00 2001 From: Yosry Ahmed Date: Tue, 11 Jun 2024 02:45:15 +0000 Subject: [PATCH] mm: zswap: add zswap_never_enabled() Add zswap_never_enabled() to skip the xarray lookup in zswap_load() if zswap was never enabled on the system. It is implemented using static branches for efficiency, as enabling zswap should be a rare event. This could shave some cycles off zswap_load() when CONFIG_ZSWAP is used but zswap is never enabled. However, the real motivation behind this patch is two-fold: - Incoming large folio swapin work will need to fallback to order-0 folios if zswap was ever enabled, because any part of the folio could be in zswap, until proper handling of large folios with zswap is added. - A warning and recovery attempt will be added in a following change in case the above was not done incorrectly. Zswap will fail the read if the folio is large and it was ever enabled. Expose zswap_never_enabled() in the header for the swapin work to use it later. [yosryahmed@google.com: expose zswap_never_enabled() in the header] Link: https://lkml.kernel.org/r/Zmjf0Dr8s9xSW41X@google.com Link: https://lkml.kernel.org/r/20240611024516.1375191-2-yosryahmed@google.com Signed-off-by: Yosry Ahmed Reviewed-by: Nhat Pham Cc: Barry Song Cc: Chengming Zhou Cc: Chris Li Cc: David Hildenbrand Cc: Johannes Weiner Cc: Matthew Wilcox (Oracle) Signed-off-by: Andrew Morton --- include/linux/zswap.h | 6 ++++++ mm/zswap.c | 10 ++++++++++ 2 files changed, 16 insertions(+) diff --git a/include/linux/zswap.h b/include/linux/zswap.h index ce5e7bfe8f1e..bf83ae5e285d 100644 --- a/include/linux/zswap.h +++ b/include/linux/zswap.h @@ -36,6 +36,7 @@ void zswap_memcg_offline_cleanup(struct mem_cgroup *memcg); void zswap_lruvec_state_init(struct lruvec *lruvec); void zswap_folio_swapin(struct folio *folio); bool zswap_is_enabled(void); +bool zswap_never_enabled(void); #else struct zswap_lruvec_state {}; @@ -65,6 +66,11 @@ static inline bool zswap_is_enabled(void) return false; } +static inline bool zswap_never_enabled(void) +{ + return false; +} + #endif #endif /* _LINUX_ZSWAP_H */ diff --git a/mm/zswap.c b/mm/zswap.c index a8c8dd8cfe6f..9d4e54282b5f 100644 --- a/mm/zswap.c +++ b/mm/zswap.c @@ -83,6 +83,7 @@ static bool zswap_pool_reached_full; static int zswap_setup(void); /* Enable/disable zswap */ +static DEFINE_STATIC_KEY_MAYBE(CONFIG_ZSWAP_DEFAULT_ON, zswap_ever_enabled); static bool zswap_enabled = IS_ENABLED(CONFIG_ZSWAP_DEFAULT_ON); static int zswap_enabled_param_set(const char *, const struct kernel_param *); @@ -136,6 +137,11 @@ bool zswap_is_enabled(void) return zswap_enabled; } +bool zswap_never_enabled(void) +{ + return !static_branch_maybe(CONFIG_ZSWAP_DEFAULT_ON, &zswap_ever_enabled); +} + /********************************* * data structures **********************************/ @@ -1557,6 +1563,9 @@ bool zswap_load(struct folio *folio) VM_WARN_ON_ONCE(!folio_test_locked(folio)); + if (zswap_never_enabled()) + return false; + /* * When reading into the swapcache, invalidate our entry. The * swapcache can be the authoritative owner of the page and @@ -1735,6 +1744,7 @@ static int zswap_setup(void) zpool_get_type(pool->zpools[0])); list_add(&pool->list, &zswap_pools); zswap_has_pool = true; + static_branch_enable(&zswap_ever_enabled); } else { pr_err("pool creation failed\n"); zswap_enabled = false;