From nobody Fri Dec 19 17:13:32 2025 Received: from mail-pl1-f182.google.com (mail-pl1-f182.google.com [209.85.214.182]) (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 44B161E884 for ; Wed, 4 Sep 2024 13:25:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.182 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725456321; cv=none; b=nEeowZXG8trPAY1yOG/pdp1fDxBUmkb9MNZiSK8i+XUNIO5hEVgAKRA8Q03/ciQoMvRfZuzcAJ4F/AaLBY4haOSmPdVmGGExQuPADEqQ7yijo6bo9lWuaFFE1+f8jnQixdqPcO9xSgMQmhTJpqzIN36Rcu1HSifXXwdOq0Rk+pY= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725456321; c=relaxed/simple; bh=H51Ud3CZIyk+NjFn1860hGhDUtqgBzkBz8CLbDVsRPQ=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=dWXfKPG3uk6m7OScmQGq+u1Rc92vGusYM+C9ygchsEIIiA1vfQNZLzbwsHtHZ165BxBXScT1MusqkKikx12CcEsb7S8xnOiA7RKOf+jBlLXM6ROFOuKnBozHTOxYM2rLe+FQSLBcDiwlEEFF9uKVZT6D9HLfhAb1uIlMbCfoqzs= 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=MuZaDfTX; arc=none smtp.client-ip=209.85.214.182 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="MuZaDfTX" Received: by mail-pl1-f182.google.com with SMTP id d9443c01a7336-20573eb852aso5248215ad.1 for ; Wed, 04 Sep 2024 06:25:20 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; t=1725456319; x=1726061119; 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=XjfNYwgRmFwRyRd2A+1fxkz5SQc6AYOk84bCepgxx8I=; b=MuZaDfTX4x7XukJn9CBUUxq5GGQ6fATJiNwB1xc1IMjoCg4K2NfD6I5+sCtgAcYSPF czSB4xcxkKLjhfCnCc/wizGGo5yp1JD5gfVNy8Julm5kYVZz8pDvDr0VUInksXSuJHQ6 orEcgJ7bVGvpt2grr32bShpbc3SCqQYNOPch0= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1725456319; x=1726061119; 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=XjfNYwgRmFwRyRd2A+1fxkz5SQc6AYOk84bCepgxx8I=; b=NAPoOjvOMcUC1YObyifj1epd1ZYvwInLQ8M8xgz5Ryivn2Kj1/2wgzIDBwhC8JtpQT 4C7qyOfHWOCAHOwMNKbpyahFIDLOKGs22e5qXRuI0LFYJLg7VGFq8pZalTjETxQN3dS1 ebcCjj+GnkCYbf6PzasMln+tuYF0SKlTiOG1PVn9WEup++JXiVjiw7EENUVz4MsPZUH2 TNBnQL6/Dns9CBxVAhbM5CqrzwReKnKy4iGT5QqsC2bkWHp17t8KVbdZR1PhGRjnTiP4 5SKdKYvr+z8Kw1m7zr4SDyeDlkxkE2jsrMDsU/1tDm5V8hjM8pQULn2Rf35pLOfe/CGO nDew== X-Forwarded-Encrypted: i=1; AJvYcCXN9hiCTOIWZ0TP78poBUMLtGM9uSGLfMDhE2aFu1x6ZjjJTFJ2JHb0aNwybw3tGvaQUV3Wfuuhr+TTnFQ=@vger.kernel.org X-Gm-Message-State: AOJu0Yyq2gyhEsMGNXTO6VS9ZD2YLhqlGL3v11VSVfac78hrAEUzcP0Q j7eP9odmA2pTL9aKb/2BMG+AcsRn/qkGjxHD6sTKdWJf+A163RhJdYATdc196DAEr9upIxn7pav 3Mw== X-Google-Smtp-Source: AGHT+IG8Z6ty2uJavX/X05eo41F80ttboNTYucuMzQ+OVRdZYEfWed8fHP7XGePjyyqABwzDlQZk3w== X-Received: by 2002:a17:902:e545:b0:1fd:6ca4:f987 with SMTP id d9443c01a7336-206b8341fdfmr38379035ad.15.1725456319545; Wed, 04 Sep 2024 06:25:19 -0700 (PDT) Received: from tigerii.tok.corp.google.com ([2401:fa00:8f:203:4132:a2a2:35bc:acba]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-206aea54e7bsm13479215ad.183.2024.09.04.06.25.17 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 04 Sep 2024 06:25:19 -0700 (PDT) From: Sergey Senozhatsky To: Minchan Kim Cc: Andrew Morton , Richard Chang , linux-kernel@vger.kernel.org, Sergey Senozhatsky Subject: [RFC PATCH 2/3] zram: rework recompress target selection logic Date: Wed, 4 Sep 2024 22:24:54 +0900 Message-ID: <20240904132508.2000743-3-senozhatsky@chromium.org> X-Mailer: git-send-email 2.46.0.469.g59c65b2a67-goog In-Reply-To: <20240904132508.2000743-1-senozhatsky@chromium.org> References: <20240904132508.2000743-1-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" Target slot selection for recompression is just a simple iteration over zram->table entries (stored pages) from slot 0 to max slot. Given that zram->table slots are written in random order and are not sorted by size, a simple iteration over slots selects suboptimal targets for recompression. This is not a problem if we recompress every single zram->table slot, but we never do that in reality. In reality we limit the number of slots we can recompress (via max_pages parameter) and hence proper slot selection becomes very important. The strategy is quite simple, suppose we have two candidate slots for recompression, one of size 48 bytes and one of size 2800 bytes, and we can recompress only one, then it certainly makes more sense to pick 2800 entry for recompression. Because even if we manage to compress 48 bytes objects even further the savings are going to be very small. Potential savings after good re-compression of 2800 bytes objects are much higher. This patch reworks slot selection and introduces the strategy described above: among candidate slots always select the biggest ones first. For that the patch introduces zram_pp_ctl (post-processing) structure which holds 16 groups of slots. Slots are assigned to a particular group based on their sizes - the larger the size of the slot the higher the group index. This, basically, sorts slots by size in liner time (we still perform just one iteration over zram->table slots). When we select slot for recompression we always first lookup in higher pp groups (those that hold the largest slots). Which achieves the desired behavior. TEST =3D=3D=3D=3D A very simple demonstration: zram is configured with zstd, and zstd with dict as a recompression stream. A limited (max 4096 pages) recompression is performed then, with a log of sizes of slots that were recompressed. You can see that patched zram selects slots for recompression in significantly different manner, which leads to higher memory savings (see column #2 of mm_stat output). BASE ---- *** initial state of zram device /sys/block/zram0/mm_stat 1750994944 504491413 514203648 0 514203648 1 0 3420= 4 34204 *** recompress idle max_pages=3D4096 /sys/block/zram0/mm_stat 1750994944 504262229 514953216 0 514203648 1 0 3420= 4 34204 Sizes of selected objects for recompression: ... 45 58 24 226 91 40 24 24 24 424 2104 93 2078 2078 2078 959 154 ... PATCHED ------- *** initial state of zram device /sys/block/zram0/mm_stat 1750982656 504492801 514170880 0 514170880 1 0 3420= 4 34204 *** recompress idle max_pages=3D4096 /sys/block/zram0/mm_stat 1750982656 503716710 517586944 0 514170880 1 0 3420= 4 34204 Sizes of selected objects for recompression: ... 2826 2861 2829 2989 2713 2583 2698 2685 2748 2617 ... Signed-off-by: Sergey Senozhatsky --- drivers/block/zram/zram_drv.c | 180 ++++++++++++++++++++++++++++------ 1 file changed, 152 insertions(+), 28 deletions(-) diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c index c91fdf399d1b..998efe3979f8 100644 --- a/drivers/block/zram/zram_drv.c +++ b/drivers/block/zram/zram_drv.c @@ -659,8 +659,9 @@ static ssize_t writeback_store(struct device *dev, goto next; =20 if (zram_test_flag(zram, index, ZRAM_WB) || - zram_test_flag(zram, index, ZRAM_SAME) || - zram_test_flag(zram, index, ZRAM_UNDER_WB)) + zram_test_flag(zram, index, ZRAM_SAME) || + zram_test_flag(zram, index, ZRAM_UNDER_WB) || + zram_test_flag(zram, index, ZRAM_PP_SLOT)) goto next; =20 if (mode & IDLE_WRITEBACK && @@ -1648,6 +1649,115 @@ static int zram_bvec_write(struct zram *zram, struc= t bio_vec *bvec, } =20 #ifdef CONFIG_ZRAM_MULTI_COMP +struct zram_pp_slot { + unsigned long index; + struct list_head entry; +}; + +#define NUM_PP_GROUPS 17 + +struct zram_pp_ctl { + struct list_head slots[NUM_PP_GROUPS]; +}; + +static void init_pp_ctl(struct zram_pp_ctl *ctl) +{ + u32 idx; + + for (idx =3D 0; idx < NUM_PP_GROUPS; idx++) + INIT_LIST_HEAD(&ctl->slots[idx]); +} + +static void release_pp_slot(struct zram *zram, struct zram_pp_slot *pps) +{ + zram_slot_lock(zram, pps->index); + if (zram_test_flag(zram, pps->index, ZRAM_PP_SLOT)) + zram_clear_flag(zram, pps->index, ZRAM_PP_SLOT); + zram_slot_unlock(zram, pps->index); + kfree(pps); +} + +static void release_pp_ctl(struct zram *zram, struct zram_pp_ctl *ctl) +{ + u32 idx; + + for (idx =3D 0; idx < NUM_PP_GROUPS; idx++) { + while (!list_empty(&ctl->slots[idx])) { + struct zram_pp_slot *pps; + + pps =3D list_first_entry(&ctl->slots[idx], + struct zram_pp_slot, + entry); + list_del_init(&pps->entry); + release_pp_slot(zram, pps); + } + } +} + +static void place_pp_slot(struct zram *zram, struct zram_pp_ctl *ctl, + struct zram_pp_slot *pps) +{ + s32 diff, idx; + + /* + * On 4K system this keeps PP slot groups 256 bytes apart. The + * higher the group IDX the larger the slot size. + */ + diff =3D PAGE_SIZE / (NUM_PP_GROUPS - 1); + idx =3D zram_get_obj_size(zram, pps->index) / diff; + list_add(&pps->entry, &ctl->slots[idx]); + + zram_set_flag(zram, pps->index, ZRAM_PP_SLOT); +} + +#define RECOMPRESS_IDLE (1 << 0) +#define RECOMPRESS_HUGE (1 << 1) + +static int scan_slots_for_recompress(struct zram *zram, u32 mode, + struct zram_pp_ctl *ctl) +{ + unsigned long nr_pages =3D zram->disksize >> PAGE_SHIFT; + struct zram_pp_slot *pps =3D NULL; + unsigned long index; + + for (index =3D 0; index < nr_pages; index++) { + if (!pps) + pps =3D kmalloc(sizeof(*pps), GFP_KERNEL); + if (!pps) + return -ENOMEM; + + INIT_LIST_HEAD(&pps->entry); + + zram_slot_lock(zram, index); + if (!zram_allocated(zram, index)) + goto next; + + if (mode & RECOMPRESS_IDLE && + !zram_test_flag(zram, index, ZRAM_IDLE)) + goto next; + + if (mode & RECOMPRESS_HUGE && + !zram_test_flag(zram, index, ZRAM_HUGE)) + goto next; + + if (zram_test_flag(zram, index, ZRAM_WB) || + zram_test_flag(zram, index, ZRAM_UNDER_WB) || + zram_test_flag(zram, index, ZRAM_PP_SLOT) || + zram_test_flag(zram, index, ZRAM_SAME) || + zram_test_flag(zram, index, ZRAM_INCOMPRESSIBLE)) + goto next; + + pps->index =3D index; + place_pp_slot(zram, ctl, pps); + pps =3D NULL; +next: + zram_slot_unlock(zram, index); + } + + kfree(pps); + return 0; +} + /* * This function will decompress (unless it's ZRAM_HUGE) the page and then * attempt to compress it using provided compression algorithm priority @@ -1655,7 +1765,7 @@ static int zram_bvec_write(struct zram *zram, struct = bio_vec *bvec, * * Corresponding ZRAM slot should be locked. */ -static int zram_recompress(struct zram *zram, u32 index, struct page *page, +static int recompress_slot(struct zram *zram, u32 index, struct page *page, u64 *num_recomp_pages, u32 threshold, u32 prio, u32 prio_max) { @@ -1675,6 +1785,7 @@ static int zram_recompress(struct zram *zram, u32 ind= ex, struct page *page, return -EINVAL; =20 comp_len_old =3D zram_get_obj_size(zram, index); + /* * Do not recompress objects that are already "small enough". */ @@ -1798,8 +1909,28 @@ static int zram_recompress(struct zram *zram, u32 in= dex, struct page *page, return 0; } =20 -#define RECOMPRESS_IDLE (1 << 0) -#define RECOMPRESS_HUGE (1 << 1) +static struct zram_pp_slot *select_slot_for_recompress(struct zram_pp_ctl = *ctl) +{ + struct zram_pp_slot *pps =3D NULL; + s32 idx =3D NUM_PP_GROUPS - 1; + + /* + * Select PP-slots starting from the highest group, which should + * give us the best candidate for recompression. + */ + while(idx > 0) { + pps =3D list_first_entry_or_null(&ctl->slots[idx], + struct zram_pp_slot, + entry); + if (pps) { + list_del_init(&pps->entry); + break; + } + + idx--; + } + return pps; +} =20 static ssize_t recompress_store(struct device *dev, struct device_attribute *attr, @@ -1807,14 +1938,16 @@ static ssize_t recompress_store(struct device *dev, { u32 prio =3D ZRAM_SECONDARY_COMP, prio_max =3D ZRAM_MAX_COMPS; struct zram *zram =3D dev_to_zram(dev); - unsigned long nr_pages =3D zram->disksize >> PAGE_SHIFT; char *args, *param, *val, *algo =3D NULL; u64 num_recomp_pages =3D ULLONG_MAX; + struct zram_pp_slot *pps; + struct zram_pp_ctl ctl; u32 mode =3D 0, threshold =3D 0; - unsigned long index; struct page *page; ssize_t ret; =20 + init_pp_ctl(&ctl); + args =3D skip_spaces(buf); while (*args) { args =3D next_arg(args, ¶m, &val); @@ -1907,36 +2040,26 @@ static ssize_t recompress_store(struct device *dev, goto release_init_lock; } =20 + scan_slots_for_recompress(zram, mode, &ctl); + ret =3D len; - for (index =3D 0; index < nr_pages; index++) { + while ((pps =3D select_slot_for_recompress(&ctl))) { int err =3D 0; =20 if (!num_recomp_pages) break; =20 - zram_slot_lock(zram, index); - - if (!zram_allocated(zram, index)) - goto next; - - if (mode & RECOMPRESS_IDLE && - !zram_test_flag(zram, index, ZRAM_IDLE)) - goto next; - - if (mode & RECOMPRESS_HUGE && - !zram_test_flag(zram, index, ZRAM_HUGE)) - goto next; - - if (zram_test_flag(zram, index, ZRAM_WB) || - zram_test_flag(zram, index, ZRAM_UNDER_WB) || - zram_test_flag(zram, index, ZRAM_SAME) || - zram_test_flag(zram, index, ZRAM_INCOMPRESSIBLE)) + zram_slot_lock(zram, pps->index); + if (!zram_test_flag(zram, pps->index, ZRAM_PP_SLOT)) goto next; =20 - err =3D zram_recompress(zram, index, page, &num_recomp_pages, - threshold, prio, prio_max); + err =3D recompress_slot(zram, pps->index, page, + &num_recomp_pages, threshold, + prio, prio_max); next: - zram_slot_unlock(zram, index); + zram_slot_unlock(zram, pps->index); + release_pp_slot(zram, pps); + if (err) { ret =3D err; break; @@ -1948,6 +2071,7 @@ static ssize_t recompress_store(struct device *dev, __free_page(page); =20 release_init_lock: + release_pp_ctl(zram, &ctl); up_read(&zram->init_lock); return ret; } --=20 2.46.0.469.g59c65b2a67-goog