From nobody Thu Dec 18 20:38:25 2025 Received: from mail-pl1-f174.google.com (mail-pl1-f174.google.com [209.85.214.174]) (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 4DB231FBC8C for ; Wed, 12 Feb 2025 06:32:08 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.174 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739341930; cv=none; b=rgor+hFsr90LeGNHM/G3K/O6h6P1RhjM7k68aEW/Kp9qRZ8c/vR5wun3jxK0rEGWFOoHqwXpCOzP4d3PgOvPRTttPWIMeheIPBDg3R8DbPK1pJZPhtj/s6WSq//1/FaiNeWMT53XuWHNPtfJYeRxcg+e1eqd7jvLu7SlL9H28DM= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739341930; c=relaxed/simple; bh=ftM5GNwd6HoMW8lSepoMzzNcEpey/3RV/ln/tuvRXA4=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=LBlN7zUFXKdnSt7PTQn+WlPnLPoYHBtszYSRU9yyIQjJe45pkzyrQRi+H01JcnlaDzRg6D8+rIAimEdPWzyO9JA2QtNvAQg/M+EUNGSnwwoOyrMPjfNsKb6SR/eFAQkXOuhvw6Q8u9srUW+6g5qsVo/LkgMdfIwFcEPRX+sf3dg= 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=TjsqoVTP; arc=none smtp.client-ip=209.85.214.174 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="TjsqoVTP" Received: by mail-pl1-f174.google.com with SMTP id d9443c01a7336-220bfdfb3f4so6530105ad.2 for ; Tue, 11 Feb 2025 22:32:08 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; t=1739341927; x=1739946727; 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=Nbviwh7jX+fyZgx+5zWo4yndOTBdlLf1Q5tRKthE6k8=; b=TjsqoVTPn4JxHTl9NQoIJJ9EddsPP/tnluhoC5vPcBaDWEfP9y5dBVa0lEVIh+d8Zl vuAF2PtxSjTjoKRKreB5S7VvZEjgfBFNF3lZEI2q8SOQsOJ2HKHUuPATsMtLFYA9BxmZ SdUOyZlXHmiWqditg6AaHTSjchxND7a2R4Bk0= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1739341927; x=1739946727; 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=Nbviwh7jX+fyZgx+5zWo4yndOTBdlLf1Q5tRKthE6k8=; b=KkhGt4sAw33P7LKOYmgxq7AbwmKnRkauIGtDjV276n9ejQMLZQYqj5g2EfyRjOGUls qRz9fm4TJvFnDuczsjUKzdGWk9j3goR7HnKzsRR6ee9BCXV1T5WMXSU23edy+BZq+Afd emtTLhjZTEroglqUemLqYoBbIfHcG1Jwkp9zfE574mKj+d3XrGwQ/eqHcLbskiHO9LKN I7JLjEf8pUvEwKk+Wc2wDUbEGhDZ9hBZvZ771BFz4CBSzS2m7KYBMdyioh+yfw2R4YQI 8aG3F0pNYd7YQDS1QYZWliI7dIZbi/G63z+O4tlS25fPyWJZT1hFei01CrkleMAhYe9t 0fjw== X-Forwarded-Encrypted: i=1; AJvYcCV0e9uupSDeCA1jB+wWqlyf8i3XKDCjQwuLjiu8aDoOthUXmrXAbirhdnGZW5yJLCtvfaEdP9CO0UVfr4U=@vger.kernel.org X-Gm-Message-State: AOJu0YzJJu3FLSvqJOFJ1YRoe3FfsKCmwPBUwe6cBGdkAZ+yDWuWzFlE YOcAzmsfWS8FB/ZWBoOgpDiiGQxkXdL4rFpMmlKa9w7QA3Hiqw9SKRvO5kkAxw== X-Gm-Gg: ASbGnctdT8m9K3Y7IIGfgSfUhAHnRyMNdN9452esHUeu2OA+cQttxaMkNqpuJiXZUub qBxU1L51boN2mIDwla/hLupNqHFrNu3PVqB/qaOTJhHHd36jJwdHMpzQ1wyBIpQ0l7LVIsIUbGE Xhf9NnV23U7u63Pd3PzXUzhxsCJSFRwjaeh8+LGNou4PC4enqk6Va4jI7gokrTNSa0qBWhSTF4N RDBSmlP+17IxpA/tc2Zg5e3cyyswuahNzTNMxfZ40DVAwjYG3ohWVPIDWeYs3V3kC2jz8OncF0i N6pkPm33KoQgzOze2Q== X-Google-Smtp-Source: AGHT+IFSvyC57xadlYDsJ2pjEf3GwKRx0RFUmqWoHBxBXjtPHZ1A+qKCAZJUZUiYg24snMECPbVRZA== X-Received: by 2002:a17:902:ea11:b0:216:46f4:7e3d with SMTP id d9443c01a7336-220bbad6f94mr31042255ad.15.1739341925761; Tue, 11 Feb 2025 22:32:05 -0800 (PST) Received: from localhost ([2401:fa00:8f:203:69f5:6852:451e:8142]) by smtp.gmail.com with UTF8SMTPSA id d9443c01a7336-220c34f443bsm2839685ad.5.2025.02.11.22.32.03 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 11 Feb 2025 22:32:05 -0800 (PST) From: Sergey Senozhatsky To: Andrew Morton Cc: Yosry Ahmed , Kairui Song , Minchan Kim , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Sergey Senozhatsky Subject: [PATCH v5 01/18] zram: sleepable entry locking Date: Wed, 12 Feb 2025 15:26:59 +0900 Message-ID: <20250212063153.179231-2-senozhatsky@chromium.org> X-Mailer: git-send-email 2.48.1.502.g6dc24dfdaf-goog In-Reply-To: <20250212063153.179231-1-senozhatsky@chromium.org> References: <20250212063153.179231-1-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 | 65 ++++++++++++++++++++++++++++------- drivers/block/zram/zram_drv.h | 20 +++++++---- 2 files changed, 67 insertions(+), 18 deletions(-) diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c index 9f5020b077c5..3708436f1d1f 100644 --- a/drivers/block/zram/zram_drv.c +++ b/drivers/block/zram/zram_drv.c @@ -58,19 +58,57 @@ 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].lockdep_map, "zram-entry->lock", + &zram->table_lockdep_key, 0); +#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_try_lock(struct zram *zram, u32 index) +{ + unsigned long *lock =3D &zram->table[index].flags; + + if (!test_and_set_bit_lock(ZRAM_ENTRY_LOCK, lock)) { +#ifdef CONFIG_DEBUG_LOCK_ALLOC + mutex_acquire(&zram->table[index].lockdep_map, 0, 1, _RET_IP_); +#endif + 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; + +#ifdef CONFIG_DEBUG_LOCK_ALLOC + mutex_acquire(&zram->table[index].lockdep_map, 0, 0, _RET_IP_); +#endif + wait_on_bit_lock(lock, ZRAM_ENTRY_LOCK, TASK_UNINTERRUPTIBLE); } =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; + +#ifdef CONFIG_DEBUG_LOCK_ALLOC + mutex_release(&zram->table[index].lockdep_map, _RET_IP_); +#endif + clear_and_wake_up_bit(ZRAM_ENTRY_LOCK, lock); } =20 static inline bool init_done(struct zram *zram) @@ -93,7 +131,6 @@ 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 +1510,11 @@ 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; @@ -2321,7 +2354,7 @@ static void zram_slot_free_notify(struct block_device= *bdev, zram =3D bdev->bd_disk->private_data; =20 atomic64_inc(&zram->stats.notify_free); - if (!zram_slot_trylock(zram, index)) { + if (!zram_slot_try_lock(zram, index)) { atomic64_inc(&zram->stats.miss_free); return; } @@ -2625,6 +2658,10 @@ static int zram_add(void) if (ret) goto out_cleanup_disk; =20 +#ifdef CONFIG_DEBUG_LOCK_ALLOC + lockdep_register_key(&zram->table_lockdep_key); +#endif + zram_debugfs_register(zram); pr_info("Added device: %s\n", zram->disk->disk_name); return device_id; @@ -2681,6 +2718,10 @@ static int zram_remove(struct zram *zram) */ zram_reset_device(zram); =20 +#ifdef CONFIG_DEBUG_LOCK_ALLOC + lockdep_unregister_key(&zram->table_lockdep_key); +#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..63b933059cb6 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 lockdep_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 table_lockdep_key; +#endif }; #endif --=20 2.48.1.502.g6dc24dfdaf-goog