From nobody Thu Dec 18 00:49:45 2025 Received: from mail-pl1-f170.google.com (mail-pl1-f170.google.com [209.85.214.170]) (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 12A252036E3 for ; Fri, 21 Feb 2025 09:38:48 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.170 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1740130730; cv=none; b=q7XYKfD+WzbypRT1rhc6gMSyy11AnZZlej4eNzhNmkiOQSEjTPWwsh6Na28XJFGcDORw1KTqo09W/PPVIVrz+Ttishbh0SqVQAqkYDi1K95ToNACrMrq/WvKhkE4HaidINj0aCLWOjcJOdbPTJhx7+LZxVao7rppV5XVtz87Gpo= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1740130730; c=relaxed/simple; bh=2PHeV8nT/CIs0wVCCrZiQbqt2KzPBiFqKqwqGxUlrRY=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=ZyUbgfGKT6Izbr8rhFGxDpvzWXhxDoxPcdeahYPzy/vjaQnTxsJc715mQfELmM9p0nvNbr2yC8noHgwUuuBAR4r7LAOBzqopJ6VhvrybzeGASJZieCOs9xKOizc45ZWlUQ5wbo1ivz+1uby25GhD/nk4alwjBGJDHqbJhmWrAuQ= 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=UQzPHBQN; arc=none smtp.client-ip=209.85.214.170 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="UQzPHBQN" Received: by mail-pl1-f170.google.com with SMTP id d9443c01a7336-220c4159f87so25834195ad.0 for ; Fri, 21 Feb 2025 01:38:48 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; t=1740130728; x=1740735528; 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=tEamf86sHM0Ptusd1ivjV+FzA+4m9NR9VbFHQMTSZrc=; b=UQzPHBQNiMxVvSgPDxEzVYSdYIRAOzIG30SyOO/8ilTW8Mz6U15c57V2VTNMUuBH1V lUR53fwlbw5nkA1bg3tmtuhkAb/DUc3lZ59V2okMdmDHA1LLSp1ETY6RTTLqhE3MfklS GJHvar3Xic033RMPRXx/Xt98NM3KfdQCeeoUE= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1740130728; x=1740735528; 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=tEamf86sHM0Ptusd1ivjV+FzA+4m9NR9VbFHQMTSZrc=; b=Jd/UE4ReB/Nuxxvqa70eljM7ggLiOp+36tdGV93TwRIYpOYs2ZEoBBf2Xu+cQjMJnP Ax1YP6K3fvVSH+oKtGet8qMjFfsVEAqtLpG86oSSTRvl0mKgXsH/WFzG+DfuQfs5p8dS cDne9HQxWR7IoRAnAq9VGXEVswSQMgC9Fx3597J044lPMiLOALfPn4N46Tpckxdn7i5R eRFn3jL9FT5Pqk8yK4CduJ6uO90FzDMMcW8Xor+KyQTufHBL05dSyGZ+XQi7lCXpp57E t1He9mkja78E34nrIDVqQvYD1tnxtzlqk7BIE6D/UJp7jqkDia3bnnIxMuqSo7s9aNUs LV4w== X-Forwarded-Encrypted: i=1; AJvYcCUDeVs9GdTJLUw/62qYCXMOTVFb9OWHuXtFU/zUjcWO+BhrhT+CMYwljG1xJlCC7f8w8u6sNoODrDJcT5Y=@vger.kernel.org X-Gm-Message-State: AOJu0YxxBFrTjeuNWOLxXbnH8dSh5OiXezDxngtsUsDu8uMYxDN9WE8+ lK4KMzoJK1vMowwR9o0MRE7oevwXK42yItPRs6rq/gspTyTOgxQ8rrTz0URIFA== X-Gm-Gg: ASbGncs2F/iHx9dIv/bYJHhzKh+jHMcfaQfJIutJdeYawKq9xoDQbtbNpfU8nmpV/Ua fxV0gDLwiPf6yN+PCF2WuK5qRzYkCm2xDsNUd4LnPWHfNrOoVN1tSXACuiSmYONTSqxSmaqRw3G w1G40QK77lFrNBNLPspak4fRNy6ZwEJPZi7joT9+WlTfxhkeHyHjwQ5dWdJTQyHQcwhMtWlObnX VkQLonqT/56C/pZGQwHUNtQ0S/u2J8lUbnx06DXkep1neOpygH0LhOdr2hCTB3SjPZwAMIC5xTB 8IB6j3+2yAiUxcx2ZalSyEWEaQs= X-Google-Smtp-Source: AGHT+IF6XPk6PTdI7TGgSavL9+4vaZz+bvaqDiLmdjUKVz/91xc480zPlBnpKvLh5Q/90+8Bn/sTSA== X-Received: by 2002:a17:903:2350:b0:21f:515:d61 with SMTP id d9443c01a7336-2219ff4e78emr42043375ad.21.1740130728316; Fri, 21 Feb 2025 01:38:48 -0800 (PST) Received: from localhost ([2401:fa00:8f:203:f987:e1e:3dbb:2191]) by smtp.gmail.com with UTF8SMTPSA id d9443c01a7336-220d556fb40sm132682925ad.193.2025.02.21.01.38.45 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); 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> 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 | 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 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 +#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 =3D &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; } =20 static void zram_slot_lock(struct zram *zram, u32 index) { - spin_lock(&zram->table[index].lock); + unsigned long *lock =3D &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_); } =20 static void zram_slot_unlock(struct zram *zram, u32 index) { - spin_unlock(&zram->table[index].lock); + unsigned long *lock =3D &zram->table[index].flags; + + mutex_release(slot_dep_map(zram, index), _RET_IP_); + clear_and_wake_up_bit(ZRAM_ENTRY_LOCK, lock); } =20 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 =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 +1515,11 @@ 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 +2663,10 @@ 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 +2723,10 @@ 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