From nobody Wed Dec 17 03:00:07 2025 Received: from mail-pj1-f44.google.com (mail-pj1-f44.google.com [209.85.216.44]) (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 B1B8217CA1B for ; Mon, 3 Mar 2025 02:24:41 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.216.44 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1740968683; cv=none; b=Jh7MyIrLDr0INay0xHqKP50yV8idmhWRNz00NuRX9BriO5Fl5rybz0Ts188sZ19gqquOUNnPMQzSSyh5kZl6K2GePdyg3xvW5ANyJSbVnH6UW2pnJkJ+IY/B/ypxVAFccYlYaI98bHtEezcwMs9EgeYIYSzA0ch+MYrpRWTs6ws= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1740968683; c=relaxed/simple; bh=Ueba+oa0oa0PlNzLN9Uzd8MRvSnqENM622OyfHdWL+o=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=rc0aAWALOqxUV8SRzZHOn8Kiux6p+wsxz0cuznukNkKS9BtURNODTdiXb6Dt91X5lpNWDSKuflYb7FWTvcqOiDAzcvebU/U19d1vbDW2YjxRObLMMOQvkVq2yjWaoh1RyA3S/4GNL7rblLoy72q/OD0DMILOQFYQMXTWjSxlw7I= 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=fcdQkdjA; arc=none smtp.client-ip=209.85.216.44 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="fcdQkdjA" Received: by mail-pj1-f44.google.com with SMTP id 98e67ed59e1d1-2f9b9c0088fso6591084a91.0 for ; Sun, 02 Mar 2025 18:24:41 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; t=1740968681; x=1741573481; 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=24epfTRD5B0/Gn0qvdHVkfmT+fNP4MZPLg9AakHcZPk=; b=fcdQkdjArD+e0N5ajKPC2TgXyj2kIraBpBQpLvB9yzX+eYZwvHH863qGOu3eTO0/5F 6zOa9pcUdPcompt4bmCo0QlqC2D8iTdD9yTi8WGEHsb/2I6RASB9EumE2aUPELfa3T2c ADgR6OFpm7Ys4MzY1QWzPICrQUxezV5Ct22Lg= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1740968681; x=1741573481; 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=24epfTRD5B0/Gn0qvdHVkfmT+fNP4MZPLg9AakHcZPk=; b=BxWHpTu3ZLBhUGlxa/PO/R/e2sKtMlQOypxchNvJVMpD9wl38gYcT2IR5NsTJL8IX3 5yLoI9hvnAu2hueLRL9xOPc30zMorEZ4Ax24HSru0WAx5KGr8fKHI3TKqnD9kICn2CYV B2vmVUT4l0RINduZIj8CZLVA26xzpXKpfOjm28uC2+o5aqtpfW9WIHyxwmKBp37FxNbX B1PfhY9+o3pi3QyTNVJiXG/Jriycs5vyE/ZW6rEJ1TnyPFQJgliDQFSGUFx35eOpe4I/ c1czYVuMkb5f/Rm9Rf3CAzqajSwI7pGqP/Axo9zbYzaZrFrjkNXO6KIw6ndAf7pI5Faq TGzg== X-Forwarded-Encrypted: i=1; AJvYcCVNrKxGz/RcDExgmbpNkExSSv/UpP8Op+cL4QkS27k7CKS6xelA9+etJEB5dEWXvWyds+8fl7vcPTxxNcc=@vger.kernel.org X-Gm-Message-State: AOJu0YzzmcCZjFWbAjhR1dYijyACkOXaQ7yT5001pNczlCFKzS05uLpd RsIWk0uAR0JLDxejT8nUp2Ig6Ko6iPjyKjPOYTa9ch7BzS7RPRSzGx4nVJdZYQ== X-Gm-Gg: ASbGncuA6TNXwRk5qsYIHWbaHwPvZMbRWgu16IxLzCIofq3ErC2S4sf/tuu8kEe8Thc V6NWJ6I52tZ/Veqgg4ZbE+O18T3OKSi79nTpwkUU5NHZueTWEwTSa7wpKBsuCz4M/0yxDQ4dxxp qARUn4hUS2jv9b0+3w2X/16dVcOzeODDMRGXfw2uxK300il7PhOQp0/WssBDBqbPxEAez+urZiV JgCReOzybKKFPZYpM1obAAwREYXh5dNkrMusnDnaGS1qcwR8hDx6G3kHaZIHpAt7iX8nk2Z05jv T9xRgMYJZrPyJYSYKfD5GWwR/GymChDGEuZf9EHuFO0/ovc= X-Google-Smtp-Source: AGHT+IEzPpFTdNA4qdxJB0dxJj4fKFXJpJ2zIhvE5aIYLQNZyq296Wz9RmH9FDhwIK3/6h7XuPIjIQ== X-Received: by 2002:a17:90b:3884:b0:2fa:2252:f436 with SMTP id 98e67ed59e1d1-2feba5ced0cmr17673056a91.3.1740968680936; Sun, 02 Mar 2025 18:24:40 -0800 (PST) Received: from localhost ([2401:fa00:8f:203:1513:4f61:a4d3:b418]) by smtp.gmail.com with UTF8SMTPSA id d9443c01a7336-223501d2610sm66715445ad.14.2025.03.02.18.24.38 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sun, 02 Mar 2025 18:24:40 -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 01/19] zram: sleepable entry locking Date: Mon, 3 Mar 2025 11:03:10 +0900 Message-ID: <20250303022425.285971-2-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> 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 | 54 ++++++++++++++++++++++++++++------- drivers/block/zram/zram_drv.h | 15 ++++++---- 2 files changed, 52 insertions(+), 17 deletions(-) diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c index 9f5020b077c5..70599d41b828 100644 --- a/drivers/block/zram/zram_drv.c +++ b/drivers/block/zram/zram_drv.c @@ -58,19 +58,56 @@ 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) +#define slot_dep_map(zram, index) (&(zram)->table[(index)].dep_map) + +static void zram_slot_lock_init(struct zram *zram, u32 index) +{ + static struct lock_class_key __key; + + lockdep_init_map(slot_dep_map(zram, index), "zram->table[index].lock", + &__key, 0); +} + +/* + * 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 spin_trylock(&zram->table[index].lock); + 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; + } + + 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 +130,6 @@ 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 +1509,11 @@ 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; diff --git a/drivers/block/zram/zram_drv.h b/drivers/block/zram/zram_drv.h index db78d7c01b9a..c804f78a7fa8 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 */ @@ -58,16 +58,19 @@ 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_ZRAM_TRACK_ENTRY_ACTIME ktime_t ac_time; #endif + struct lockdep_map dep_map; }; =20 struct zram_stats { --=20 2.48.1.711.g2feabab25a-goog