From nobody Fri Dec 19 20:00:39 2025 Received: from mail-pj1-f54.google.com (mail-pj1-f54.google.com [209.85.216.54]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1B299188704 for ; Fri, 14 Feb 2025 04:52:25 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.216.54 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739508747; cv=none; b=uJhnaMTaBQ1pNRYYMXoYaPGTDf9jE4tDDKI6wNxBMCT/yRiJ8b8oHLyaYYgpCulUnI0f4P+862sndbghypBrwujo/nuh9kua/zRLWTo9CcQFPCKUMouEqgYdnE7N7OEHj1nfZAUtwlXQ9aHOD5vrJejgfPE8+LbVsWPgRT90Mt0= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739508747; c=relaxed/simple; bh=Blyd3YPW6njqDUqhcU13sU79nqRZ3wtUsF7vCotFKpw=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=Vole9joegakjdZIfTYsRKzq0csD8VWC3UNJ6dkCjxPeDL2xQ/LrJC1YjOM8HsMMq/A1iiTf/4nU2cy8OjfHyA7WyuP4ddMSjyV0dyQaVx3l3A0t5m+jMQJDxk6caCfybCpMLjMNQAg4lilO8lx1PPHul2GFv7EfLvuwqOOxiuZg= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=chromium.org; spf=pass smtp.mailfrom=chromium.org; dkim=pass (1024-bit key) header.d=chromium.org header.i=@chromium.org header.b=OMYBkowV; arc=none smtp.client-ip=209.85.216.54 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=chromium.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=chromium.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=chromium.org header.i=@chromium.org header.b="OMYBkowV" Received: by mail-pj1-f54.google.com with SMTP id 98e67ed59e1d1-2fa1a3c88c5so2431422a91.3 for ; Thu, 13 Feb 2025 20:52:25 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; t=1739508745; x=1740113545; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=8Ip299Sr+pOGhTseTfOOpc4VtCVbO+2qU2TEqvTRYlA=; b=OMYBkowV2nv1mZuyOh3ftnd8ohDjP7mAAp3Zg8yZw+SYVhqurETqOOAuBj0eMpNW3G 4LkuXOcnLyMCh4sNaDvsvKC0woLUp8hsqHMemUiDM2yjtvrL02bfgfXCvj+1ccFQwyR1 C7LJjQ24dEreiZ6xxsOMchOOZ7B6fSczz3ahY= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1739508745; x=1740113545; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=8Ip299Sr+pOGhTseTfOOpc4VtCVbO+2qU2TEqvTRYlA=; b=dlkzhqZkw/NNaHlqNhbXl2uw6o7o8IPP+zMLrNP0oJNHDQuwVgZCmqSKb7Bsc3hZL0 GfKoKkCsdbOsLA3sM6miiczKD18bGOPIYdE8QLxvxCjQv6YJ7CrqHoi6DSgkT1ZDar02 uyu08mwAtFkEZvL5ViMFtsfVBNdmn7LKRdsZSv2a84yO9rcpHRl29+2gK1cLLfHJ2qZU v1ElmUKFBtIOL3bDjfWqJB8UfhLlBXe9ts39YhDDMVkInddfIJnbdhYeaHEw5L+4YGz7 MjW4aEj4PUBMEH4FXq5utw9Yj4MUq9BoxOVNr3sjdoiwP1z97b9E233NAt1dyOkzOs3B NzDw== X-Forwarded-Encrypted: i=1; AJvYcCVOaCacqKUrEz2zpKfzzjdYCSzlGn42YFkMQ6azyB6uRVYkSppV0i/FW4mqlnjSFiVQe5EGXPDWHyncXLg=@vger.kernel.org X-Gm-Message-State: AOJu0YzwyPKbzBkB6i5l49UOcmkKKzk5H4wzlzIndYbrIlQgMFdVmYob xC5q3pYuKihGzrpz5jVDcBYEaXgl761vCNCV1ehcWutGwDjsxJXHX4pne6jG8g== X-Gm-Gg: ASbGncsqYYrlwtTlLzEbWxP7E3jEtDp/lp/qIMcG6g+dokpEGKKOLy7lLElY4HzKTG4 qfwxQxUBdtNyoTVK9Nm35RweznlOCHCxn6EbvrFQ8A1LoOg8GYiG2v0udKbAwumVjeQrzWlCE7M 8JBNnHL6IWPZcXTqeDWKKbdsgNXyC4kD/EeuLqIaRKbFFMH3cwkCLO6g/1GIO/crN/2XSQMC936 3PGhHNCsOoLoQgD5YIez74WukP9qRr2duaEcX6u+VAml+BjdvU/8pSBTNNmS6A4ewDEw1AhMwmp eY1jmqMkP6uUcUxMZA== X-Google-Smtp-Source: AGHT+IElhSM58kSia8Ygok9EIOPYpgVDSk1Jw5b34RsIuUpVrp592z+ExnE3ByHbPmlZ4fx+OfAh+g== X-Received: by 2002:a05:6a00:3989:b0:729:a31:892d with SMTP id d2e1a72fcca58-7322c591baemr18875311b3a.8.1739508745187; Thu, 13 Feb 2025 20:52:25 -0800 (PST) Received: from localhost ([2401:fa00:8f:203:942d:9291:22aa:8126]) by smtp.gmail.com with UTF8SMTPSA id d2e1a72fcca58-7324f64a39asm588836b3a.69.2025.02.13.20.52.22 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 13 Feb 2025 20:52:24 -0800 (PST) From: Sergey Senozhatsky To: Andrew Morton Cc: Yosry Ahmed , Hillf Danton , Kairui Song , Minchan Kim , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Sergey Senozhatsky Subject: [PATCH v6 01/17] zram: sleepable entry locking Date: Fri, 14 Feb 2025 13:50:13 +0900 Message-ID: <20250214045208.1388854-2-senozhatsky@chromium.org> X-Mailer: git-send-email 2.48.1.601.g30ceb7b040-goog In-Reply-To: <20250214045208.1388854-1-senozhatsky@chromium.org> References: <20250214045208.1388854-1-senozhatsky@chromium.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" 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 | 105 ++++++++++++++++++++++++++++++---- drivers/block/zram/zram_drv.h | 20 +++++-- 2 files changed, 108 insertions(+), 17 deletions(-) diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c index 9f5020b077c5..65e16117f2db 100644 --- a/drivers/block/zram/zram_drv.c +++ b/drivers/block/zram/zram_drv.c @@ -58,19 +58,99 @@ static void zram_free_page(struct zram *zram, size_t in= dex); static int zram_read_from_zspool(struct zram *zram, struct page *page, u32 index); =20 -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 +static inline bool __slot_trylock(struct zram *zram, u32 index) +{ + struct lockdep_map *dep_map =3D &zram->table[index].dep_map; + unsigned long *lock =3D &zram->table[index].flags; + + if (!test_and_set_bit_lock(ZRAM_ENTRY_LOCK, lock)) { + mutex_acquire(dep_map, 0, 1, _RET_IP_); + lock_acquired(dep_map, _RET_IP_); + return true; + } + + lock_contended(dep_map, _RET_IP_); + return false; +} + +static inline void __slot_lock(struct zram *zram, u32 index) +{ + struct lockdep_map *dep_map =3D &zram->table[index].dep_map; + unsigned long *lock =3D &zram->table[index].flags; + + mutex_acquire(dep_map, 0, 0, _RET_IP_); + wait_on_bit_lock(lock, ZRAM_ENTRY_LOCK, TASK_UNINTERRUPTIBLE); + lock_acquired(dep_map, _RET_IP_); +} + +static inline void __slot_unlock(struct zram *zram, u32 index) +{ + struct lockdep_map *dep_map =3D &zram->table[index].dep_map; + unsigned long *lock =3D &zram->table[index].flags; + + mutex_release(dep_map, _RET_IP_); + clear_and_wake_up_bit(ZRAM_ENTRY_LOCK, lock); +} +#else +static inline bool __slot_trylock(struct zram *zram, u32 index) +{ + unsigned long *lock =3D &zram->table[index].flags; + + if (!test_and_set_bit_lock(ZRAM_ENTRY_LOCK, lock)) + return true; + return false; +} + +static inline void __slot_lock(struct zram *zram, u32 index) +{ + unsigned long *lock =3D &zram->table[index].flags; + + wait_on_bit_lock(lock, ZRAM_ENTRY_LOCK, TASK_UNINTERRUPTIBLE); +} + +static inline void __slot_unlock(struct zram *zram, u32 index) +{ + unsigned long *lock =3D &zram->table[index].flags; + + clear_and_wake_up_bit(ZRAM_ENTRY_LOCK, lock); +} +#endif /* CONFIG_DEBUG_LOCK_ALLOC */ + +/* + * 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) +{ + return __slot_trylock(zram, index); } =20 static void zram_slot_lock(struct zram *zram, u32 index) { - spin_lock(&zram->table[index].lock); + return __slot_lock(zram, index); } =20 static void zram_slot_unlock(struct zram *zram, u32 index) { - spin_unlock(&zram->table[index].lock); + return __slot_unlock(zram, index); } =20 static inline bool init_done(struct zram *zram) @@ -93,7 +173,6 @@ static void zram_set_handle(struct zram *zram, u32 index= , unsigned long handle) zram->table[index].handle =3D handle; } =20 -/* 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 +1552,11 @@ static bool zram_meta_alloc(struct zram *zram, u64 = disksize) huge_class_size =3D zs_huge_class_size(zram->mem_pool); =20 for (index =3D 0; index < num_pages; index++) - spin_lock_init(&zram->table[index].lock); + zram_slot_lock_init(zram, index); + return true; } =20 -/* - * 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 +2700,10 @@ static int zram_add(void) if (ret) goto out_cleanup_disk; =20 +#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 +2760,10 @@ static int zram_remove(struct zram *zram) */ zram_reset_device(zram); =20 +#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)) =20 - /* * 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 =3D 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, }; =20 -/*-- 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 --=20 2.48.1.601.g30ceb7b040-goog