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Sun, 02 Mar 2025 18:25:37 -0800 (PST) From: Sergey Senozhatsky To: Andrew Morton Cc: Yosry Ahmed , Hillf Danton , Kairui Song , Sebastian Andrzej Siewior , Minchan Kim , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Sergey Senozhatsky Subject: [PATCH v10 13/19] zsmalloc: sleepable zspage reader-lock Date: Mon, 3 Mar 2025 11:03:22 +0900 Message-ID: <20250303022425.285971-14-senozhatsky@chromium.org> X-Mailer: git-send-email 2.48.1.711.g2feabab25a-goog In-Reply-To: <20250303022425.285971-1-senozhatsky@chromium.org> References: <20250303022425.285971-1-senozhatsky@chromium.org> MIME-Version: 1.0 X-Rspam-User: X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: BD66718000D X-Stat-Signature: q8pqyfn8ms3hjbj6oaanhp1nkmiopg61 X-HE-Tag: 1740968738-367279 X-HE-Meta: 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 Z6muuNbD BiLeY01kKb0marVlxEdpqKZxfiuBiUgbQFN6r7XqXXlkON00p7sv9iIIu0PutVEVmiBiiTc0hJqg5B0h1c/1Eo85I5AGL8pNrCaSAc76BpLOOsQrqQzIAOyEGERsl22acL93PaXxzYLvPzQ6sH578rmJV2dz9bFpbVGaw4OZbbc3dFZEW01LMjnr2Og2cAZotMB9v4pzqDWKDo3dwke7jf7JEKbrnniJ65V20+YXa9aOMj0IiLHDmXhn254iFH8jsucqqrRV8cwiC0tZQ8I4axpZbd9EeG3zjj/llJsiUeHNfPAndJutDxBcpIdhJWshJOsCnrcTu4a84UsU= 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: In order to implement preemptible object mapping we need a zspage lock that satisfies several preconditions: - it should be reader-write type of a lock - it should be possible to hold it from any context, but also being preemptible if the context allows it - we never sleep while acquiring but can sleep while holding in read mode An rwsemaphore doesn't suffice, due to atomicity requirements, rwlock doesn't satisfy due to reader-preemptability requirement. It's also worth to mention, that per-zspage rwsem is a little too memory heavy (we can easily have double digits megabytes used only on rwsemaphores). Switch over from rwlock_t to a atomic_t-based implementation of a reader-writer semaphore that satisfies all of the preconditions. The spin-lock based zspage_lock is suggested by Hillf Danton. Suggested-by: Hillf Danton Signed-off-by: Sergey Senozhatsky --- mm/zsmalloc.c | 166 ++++++++++++++++++++++++++++++++++---------------- 1 file changed, 114 insertions(+), 52 deletions(-) diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c index 1424ee73cbb5..afbd72363731 100644 --- a/mm/zsmalloc.c +++ b/mm/zsmalloc.c @@ -257,6 +257,15 @@ static inline void free_zpdesc(struct zpdesc *zpdesc) __free_page(page); } +#define ZS_PAGE_UNLOCKED 0 +#define ZS_PAGE_WRLOCKED -1 + +struct zspage_lock { + spinlock_t lock; + int cnt; + struct lockdep_map dep_map; +}; + struct zspage { struct { unsigned int huge:HUGE_BITS; @@ -269,7 +278,7 @@ struct zspage { struct zpdesc *first_zpdesc; struct list_head list; /* fullness list */ struct zs_pool *pool; - rwlock_t lock; + struct zspage_lock zsl; }; struct mapping_area { @@ -279,6 +288,84 @@ struct mapping_area { enum zs_mapmode vm_mm; /* mapping mode */ }; +static void zspage_lock_init(struct zspage *zspage) +{ + static struct lock_class_key __key; + struct zspage_lock *zsl = &zspage->zsl; + + lockdep_init_map(&zsl->dep_map, "zspage->lock", &__key, 0); + spin_lock_init(&zsl->lock); + zsl->cnt = ZS_PAGE_UNLOCKED; +} + +/* + * The zspage lock can be held from atomic contexts, but it needs to remain + * preemptible when held for reading because it remains held outside of those + * atomic contexts, otherwise we unnecessarily lose preemptibility. + * + * To achieve this, the following rules are enforced on readers and writers: + * + * - Writers are blocked by both writers and readers, while readers are only + * blocked by writers (i.e. normal rwlock semantics). + * + * - Writers are always atomic (to allow readers to spin waiting for them). + * + * - Writers always use trylock (as the lock may be held be sleeping readers). + * + * - Readers may spin on the lock (as they can only wait for atomic writers). + * + * - Readers may sleep while holding the lock (as writes only use trylock). + */ +static void zspage_read_lock(struct zspage *zspage) +{ + struct zspage_lock *zsl = &zspage->zsl; + + rwsem_acquire_read(&zsl->dep_map, 0, 0, _RET_IP_); + + spin_lock(&zsl->lock); + zsl->cnt++; + spin_unlock(&zsl->lock); + + lock_acquired(&zsl->dep_map, _RET_IP_); +} + +static void zspage_read_unlock(struct zspage *zspage) +{ + struct zspage_lock *zsl = &zspage->zsl; + + rwsem_release(&zsl->dep_map, _RET_IP_); + + spin_lock(&zsl->lock); + zsl->cnt--; + spin_unlock(&zsl->lock); +} + +static __must_check bool zspage_write_trylock(struct zspage *zspage) +{ + struct zspage_lock *zsl = &zspage->zsl; + + spin_lock(&zsl->lock); + if (zsl->cnt == ZS_PAGE_UNLOCKED) { + zsl->cnt = ZS_PAGE_WRLOCKED; + rwsem_acquire(&zsl->dep_map, 0, 1, _RET_IP_); + lock_acquired(&zsl->dep_map, _RET_IP_); + return true; + } + + spin_unlock(&zsl->lock); + return false; +} + +static void zspage_write_unlock(struct zspage *zspage) +{ + struct zspage_lock *zsl = &zspage->zsl; + + rwsem_release(&zsl->dep_map, _RET_IP_); + + zsl->cnt = ZS_PAGE_UNLOCKED; + spin_unlock(&zsl->lock); +} + /* huge object: pages_per_zspage == 1 && maxobj_per_zspage == 1 */ static void SetZsHugePage(struct zspage *zspage) { @@ -290,12 +377,6 @@ static bool ZsHugePage(struct zspage *zspage) return zspage->huge; } -static void migrate_lock_init(struct zspage *zspage); -static void migrate_read_lock(struct zspage *zspage); -static void migrate_read_unlock(struct zspage *zspage); -static void migrate_write_lock(struct zspage *zspage); -static void migrate_write_unlock(struct zspage *zspage); - #ifdef CONFIG_COMPACTION static void kick_deferred_free(struct zs_pool *pool); static void init_deferred_free(struct zs_pool *pool); @@ -992,7 +1073,9 @@ static struct zspage *alloc_zspage(struct zs_pool *pool, return NULL; zspage->magic = ZSPAGE_MAGIC; - migrate_lock_init(zspage); + zspage->pool = pool; + zspage->class = class->index; + zspage_lock_init(zspage); for (i = 0; i < class->pages_per_zspage; i++) { struct zpdesc *zpdesc; @@ -1015,8 +1098,6 @@ static struct zspage *alloc_zspage(struct zs_pool *pool, create_page_chain(class, zspage, zpdescs); init_zspage(class, zspage); - zspage->pool = pool; - zspage->class = class->index; return zspage; } @@ -1217,7 +1298,7 @@ void *zs_map_object(struct zs_pool *pool, unsigned long handle, * zs_unmap_object API so delegate the locking from class to zspage * which is smaller granularity. */ - migrate_read_lock(zspage); + zspage_read_lock(zspage); read_unlock(&pool->lock); class = zspage_class(pool, zspage); @@ -1277,7 +1358,7 @@ void zs_unmap_object(struct zs_pool *pool, unsigned long handle) } local_unlock(&zs_map_area.lock); - migrate_read_unlock(zspage); + zspage_read_unlock(zspage); } EXPORT_SYMBOL_GPL(zs_unmap_object); @@ -1671,18 +1752,18 @@ static void lock_zspage(struct zspage *zspage) /* * Pages we haven't locked yet can be migrated off the list while we're * trying to lock them, so we need to be careful and only attempt to - * lock each page under migrate_read_lock(). Otherwise, the page we lock + * lock each page under zspage_read_lock(). Otherwise, the page we lock * may no longer belong to the zspage. This means that we may wait for * the wrong page to unlock, so we must take a reference to the page - * prior to waiting for it to unlock outside migrate_read_lock(). + * prior to waiting for it to unlock outside zspage_read_lock(). */ while (1) { - migrate_read_lock(zspage); + zspage_read_lock(zspage); zpdesc = get_first_zpdesc(zspage); if (zpdesc_trylock(zpdesc)) break; zpdesc_get(zpdesc); - migrate_read_unlock(zspage); + zspage_read_unlock(zspage); zpdesc_wait_locked(zpdesc); zpdesc_put(zpdesc); } @@ -1693,41 +1774,16 @@ static void lock_zspage(struct zspage *zspage) curr_zpdesc = zpdesc; } else { zpdesc_get(zpdesc); - migrate_read_unlock(zspage); + zspage_read_unlock(zspage); zpdesc_wait_locked(zpdesc); zpdesc_put(zpdesc); - migrate_read_lock(zspage); + zspage_read_lock(zspage); } } - migrate_read_unlock(zspage); + zspage_read_unlock(zspage); } #endif /* CONFIG_COMPACTION */ -static void migrate_lock_init(struct zspage *zspage) -{ - rwlock_init(&zspage->lock); -} - -static void migrate_read_lock(struct zspage *zspage) __acquires(&zspage->lock) -{ - read_lock(&zspage->lock); -} - -static void migrate_read_unlock(struct zspage *zspage) __releases(&zspage->lock) -{ - read_unlock(&zspage->lock); -} - -static void migrate_write_lock(struct zspage *zspage) -{ - write_lock(&zspage->lock); -} - -static void migrate_write_unlock(struct zspage *zspage) -{ - write_unlock(&zspage->lock); -} - #ifdef CONFIG_COMPACTION static const struct movable_operations zsmalloc_mops; @@ -1785,9 +1841,6 @@ static int zs_page_migrate(struct page *newpage, struct page *page, VM_BUG_ON_PAGE(!zpdesc_is_isolated(zpdesc), zpdesc_page(zpdesc)); - /* We're committed, tell the world that this is a Zsmalloc page. */ - __zpdesc_set_zsmalloc(newzpdesc); - /* The page is locked, so this pointer must remain valid */ zspage = get_zspage(zpdesc); pool = zspage->pool; @@ -1803,8 +1856,15 @@ static int zs_page_migrate(struct page *newpage, struct page *page, * the class lock protects zpage alloc/free in the zspage. */ spin_lock(&class->lock); - /* the migrate_write_lock protects zpage access via zs_map_object */ - migrate_write_lock(zspage); + /* the zspage write_lock protects zpage access via zs_map_object */ + if (!zspage_write_trylock(zspage)) { + spin_unlock(&class->lock); + write_unlock(&pool->lock); + return -EINVAL; + } + + /* We're committed, tell the world that this is a Zsmalloc page. */ + __zpdesc_set_zsmalloc(newzpdesc); offset = get_first_obj_offset(zpdesc); s_addr = kmap_local_zpdesc(zpdesc); @@ -1835,7 +1895,7 @@ static int zs_page_migrate(struct page *newpage, struct page *page, */ write_unlock(&pool->lock); spin_unlock(&class->lock); - migrate_write_unlock(zspage); + zspage_write_unlock(zspage); zpdesc_get(newzpdesc); if (zpdesc_zone(newzpdesc) != zpdesc_zone(zpdesc)) { @@ -1971,9 +2031,11 @@ static unsigned long __zs_compact(struct zs_pool *pool, if (!src_zspage) break; - migrate_write_lock(src_zspage); + if (!zspage_write_trylock(src_zspage)) + break; + migrate_zspage(pool, src_zspage, dst_zspage); - migrate_write_unlock(src_zspage); + zspage_write_unlock(src_zspage); fg = putback_zspage(class, src_zspage); if (fg == ZS_INUSE_RATIO_0) {