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Fri, 21 Feb 2025 01:38:47 -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 v7 01/17] zram: sleepable entry locking Date: Fri, 21 Feb 2025 18:37:54 +0900 Message-ID: <20250221093832.1949691-2-senozhatsky@chromium.org> X-Mailer: git-send-email 2.48.1.601.g30ceb7b040-goog In-Reply-To: <20250221093832.1949691-1-senozhatsky@chromium.org> References: <20250221093832.1949691-1-senozhatsky@chromium.org> MIME-Version: 1.0 X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 5AE1BC0004 X-Stat-Signature: 5ot45gfjn77p6xn4jazmcxwj8js1qtd7 X-HE-Tag: 1740130729-565502 X-HE-Meta: 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 cpTx5hJV ALf5/cvadO7iYrL6q2KHAs6MchJBlJmAV+MFT/OvjPv1CRpSQlmrHjJXc2Bg3FZqACcZFRRFH3OzL1CofYNsb8JDDmtcsFgOBhpUsxAL7G0AJG+FDJPKSrYL7sPHf4ikq9vkplBUWMs6Ka+jTUfQEYQI+tAV+8AE/4+Q0IYUEpQctl5aJvVMOCI309kIa5owXhVdRY9rtSj9hKazUkbvljB6NxdGHJhzuEd8XZb+HxfoVw/NwHuza4aaanOIv7JmHXiQFHElMJMOdOyLa7zweHfYnvyg5oWkHo6lMzRJAQayoTZyRgDt1uuN8SA== 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: Concurrent modifications of meta table entries is now handled by per-entry spin-lock. This has a number of shortcomings. First, this imposes atomic requirements on compression backends. zram can call both zcomp_compress() and zcomp_decompress() under entry spin-lock, which implies that we can use only compression algorithms that don't schedule/sleep/wait during compression and decompression. This, for instance, makes it impossible to use some of the ASYNC compression algorithms (H/W compression, etc.) implementations. Second, this can potentially trigger watchdogs. For example, entry re-compression with secondary algorithms is performed under entry spin-lock. Given that we chain secondary compression algorithms and that some of them can be configured for best compression ratio (and worst compression speed) zram can stay under spin-lock for quite some time. Having a per-entry mutex (or, for instance, a rw-semaphore) significantly increases sizeof() of each entry and hence the meta table. Therefore entry locking returns back to bit locking, as before, however, this time also preempt-rt friendly, because if waits-on-bit instead of spinning-on-bit. Lock owners are also now permitted to schedule, which is a first step on the path of making zram non-atomic. Signed-off-by: Sergey Senozhatsky --- drivers/block/zram/zram_drv.c | 68 +++++++++++++++++++++++++++++------ drivers/block/zram/zram_drv.h | 20 +++++++---- 2 files changed, 71 insertions(+), 17 deletions(-) diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c index 9f5020b077c5..31bce7c3ce8b 100644 --- a/drivers/block/zram/zram_drv.c +++ b/drivers/block/zram/zram_drv.c @@ -58,19 +58,62 @@ static void zram_free_page(struct zram *zram, size_t index); static int zram_read_from_zspool(struct zram *zram, struct page *page, u32 index); -static int zram_slot_trylock(struct zram *zram, u32 index) +static void zram_slot_lock_init(struct zram *zram, u32 index) { - return spin_trylock(&zram->table[index].lock); +#ifdef CONFIG_DEBUG_LOCK_ALLOC + lockdep_init_map(&zram->table[index].dep_map, + "zram->table[index].lock", + &zram->lock_class, 0); +#endif +} + +#ifdef CONFIG_DEBUG_LOCK_ALLOC +#define slot_dep_map(zram, index) (&(zram)->table[(index)].dep_map) +#else +#define slot_dep_map(zram, index) NULL +#endif + +/* + * entry locking rules: + * + * 1) Lock is exclusive + * + * 2) lock() function can sleep waiting for the lock + * + * 3) Lock owner can sleep + * + * 4) Use TRY lock variant when in atomic context + * - must check return value and handle locking failers + */ +static __must_check bool zram_slot_trylock(struct zram *zram, u32 index) +{ + unsigned long *lock = &zram->table[index].flags; + + if (!test_and_set_bit_lock(ZRAM_ENTRY_LOCK, lock)) { + mutex_acquire(slot_dep_map(zram, index), 0, 1, _RET_IP_); + lock_acquired(slot_dep_map(zram, index), _RET_IP_); + return true; + } + + lock_contended(slot_dep_map(zram, index), _RET_IP_); + return false; } static void zram_slot_lock(struct zram *zram, u32 index) { - spin_lock(&zram->table[index].lock); + unsigned long *lock = &zram->table[index].flags; + + mutex_acquire(slot_dep_map(zram, index), 0, 0, _RET_IP_); + wait_on_bit_lock(lock, ZRAM_ENTRY_LOCK, TASK_UNINTERRUPTIBLE); + lock_acquired(slot_dep_map(zram, index), _RET_IP_); } static void zram_slot_unlock(struct zram *zram, u32 index) { - spin_unlock(&zram->table[index].lock); + unsigned long *lock = &zram->table[index].flags; + + mutex_release(slot_dep_map(zram, index), _RET_IP_); + clear_and_wake_up_bit(ZRAM_ENTRY_LOCK, lock); } static inline bool init_done(struct zram *zram) @@ -93,7 +136,6 @@ static void zram_set_handle(struct zram *zram, u32 index, unsigned long handle) zram->table[index].handle = handle; } -/* flag operations require table entry bit_spin_lock() being held */ static bool zram_test_flag(struct zram *zram, u32 index, enum zram_pageflags flag) { @@ -1473,15 +1515,11 @@ static bool zram_meta_alloc(struct zram *zram, u64 disksize) huge_class_size = zs_huge_class_size(zram->mem_pool); for (index = 0; index < num_pages; index++) - spin_lock_init(&zram->table[index].lock); + zram_slot_lock_init(zram, index); + return true; } -/* - * To protect concurrent access to the same index entry, - * caller should hold this table index entry's bit_spinlock to - * indicate this index entry is accessing. - */ static void zram_free_page(struct zram *zram, size_t index) { unsigned long handle; @@ -2625,6 +2663,10 @@ static int zram_add(void) if (ret) goto out_cleanup_disk; +#ifdef CONFIG_DEBUG_LOCK_ALLOC + lockdep_register_key(&zram->lock_class); +#endif + zram_debugfs_register(zram); pr_info("Added device: %s\n", zram->disk->disk_name); return device_id; @@ -2681,6 +2723,10 @@ static int zram_remove(struct zram *zram) */ zram_reset_device(zram); +#ifdef CONFIG_DEBUG_LOCK_ALLOC + lockdep_unregister_key(&zram->lock_class); +#endif + put_disk(zram->disk); kfree(zram); return 0; diff --git a/drivers/block/zram/zram_drv.h b/drivers/block/zram/zram_drv.h index db78d7c01b9a..794c9234e627 100644 --- a/drivers/block/zram/zram_drv.h +++ b/drivers/block/zram/zram_drv.h @@ -28,7 +28,6 @@ #define ZRAM_SECTOR_PER_LOGICAL_BLOCK \ (1 << (ZRAM_LOGICAL_BLOCK_SHIFT - SECTOR_SHIFT)) - /* * ZRAM is mainly used for memory efficiency so we want to keep memory * footprint small and thus squeeze size and zram pageflags into a flags @@ -46,6 +45,7 @@ /* Flags for zram pages (table[page_no].flags) */ enum zram_pageflags { ZRAM_SAME = ZRAM_FLAG_SHIFT, /* Page consists the same element */ + ZRAM_ENTRY_LOCK, /* entry access lock bit */ ZRAM_WB, /* page is stored on backing_device */ ZRAM_PP_SLOT, /* Selected for post-processing */ ZRAM_HUGE, /* Incompressible page */ @@ -58,13 +58,18 @@ enum zram_pageflags { __NR_ZRAM_PAGEFLAGS, }; -/*-- Data structures */ - -/* Allocated for each disk page */ +/* + * Allocated for each disk page. We use bit-lock (ZRAM_ENTRY_LOCK bit + * of flags) to save memory. There can be plenty of entries and standard + * locking primitives (e.g. mutex) will significantly increase sizeof() + * of each entry and hence of the meta table. + */ struct zram_table_entry { unsigned long handle; - unsigned int flags; - spinlock_t lock; + unsigned long flags; +#ifdef CONFIG_DEBUG_LOCK_ALLOC + struct lockdep_map dep_map; +#endif #ifdef CONFIG_ZRAM_TRACK_ENTRY_ACTIME ktime_t ac_time; #endif @@ -137,5 +142,8 @@ struct zram { struct dentry *debugfs_dir; #endif atomic_t pp_in_progress; +#ifdef CONFIG_DEBUG_LOCK_ALLOC + struct lock_class_key lock_class; +#endif }; #endif