From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 3B8FCCCF9F8 for ; Wed, 5 Nov 2025 06:48:42 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 7A3B68E0003; Wed, 5 Nov 2025 01:48:41 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 7542E8E0002; Wed, 5 Nov 2025 01:48:41 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 642318E0003; Wed, 5 Nov 2025 01:48:41 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0014.hostedemail.com [216.40.44.14]) by kanga.kvack.org (Postfix) with ESMTP id 4AEDF8E0002 for ; Wed, 5 Nov 2025 01:48:41 -0500 (EST) Received: from smtpin29.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay09.hostedemail.com (Postfix) with ESMTP id CE0F6864DB for ; Wed, 5 Nov 2025 06:48:40 +0000 (UTC) X-FDA: 84075625200.29.F5B9805 Received: from out203-205-221-221.mail.qq.com (out203-205-221-221.mail.qq.com [203.205.221.221]) by imf08.hostedemail.com (Postfix) with ESMTP id EFEF5160004 for ; Wed, 5 Nov 2025 06:48:37 +0000 (UTC) Authentication-Results: imf08.hostedemail.com; dkim=pass header.d=foxmail.com header.s=s201512 header.b=fBwuo9Oo; dmarc=pass (policy=none) header.from=foxmail.com; spf=pass (imf08.hostedemail.com: domain of ywen.chen@foxmail.com designates 203.205.221.221 as permitted sender) smtp.mailfrom=ywen.chen@foxmail.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1762325318; a=rsa-sha256; cv=none; b=ZLIo1KY8JBnNNruXklh8Vp5/wvE1qt7piBK8isDnQpSbzQqee8Qfzc5PTbB5gDxALe5FQK cn1EFI/BTTb1cZaSuwx/MctU8OsW0MlFD3Il1g9EkZQ1LsRSBVeov+B8T6gAMRFjP2ohK3 5BVdB8V0tX28Q5zuUcFCTgluhAv9H6Q= ARC-Authentication-Results: i=1; imf08.hostedemail.com; dkim=pass header.d=foxmail.com header.s=s201512 header.b=fBwuo9Oo; dmarc=pass (policy=none) header.from=foxmail.com; spf=pass (imf08.hostedemail.com: domain of ywen.chen@foxmail.com designates 203.205.221.221 as permitted sender) smtp.mailfrom=ywen.chen@foxmail.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1762325318; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=mq0JclBaKBy4TWJ/ryyvsbPzM+n7z5k9LWVUwRw09pg=; b=JtgWZg+qvUu7eJRf6YWJFhksbxupCnKnkuBFBs8bj7jBuXFAG2Va5BP0GnogLob7cjX1+7 0qWKDU2pfEF7rPF9LdpCaEcbKPAVYrNwPFOe+hftavaBJxx631f4O8DGpyYsQsaijapLx7 h/JPIptNevA4t0cQZKo423U6bYMYQGE= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=foxmail.com; s=s201512; t=1762325312; bh=mq0JclBaKBy4TWJ/ryyvsbPzM+n7z5k9LWVUwRw09pg=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=fBwuo9Ooq62rV4AK4peYDAo7vU7VFLQYQPfFGe2OLvcegO8T2mBvfD0DhulwmXE8h L8Hhx4meoz0cRWpb6RueI2BwHJ/FTSnMEO9jdD92/aWwhF2vajyqha1lexTU/8Q501 ZTlqksPpgot1oj1BbR6cpShNlrsLUF3gnYRl4AaQ= Received: from meizu-Precision-3660.meizu.com ([112.91.84.72]) by newxmesmtplogicsvrszc43-0.qq.com (NewEsmtp) with SMTP id C09020D0; Wed, 05 Nov 2025 14:48:09 +0800 X-QQ-mid: xmsmtpt1762325289tzwix3fmp Message-ID: X-QQ-XMAILINFO: MfXlhb1xJpsOoWvb9KDTSsn7+G3+IQwE/kGDDi09Bd4UMOaaXP8X4IJ2J3rzLL MUSe1cNV5v19tJRYJSI1BAfSvmtabJBs+6WgDlzlkoF+gHPYEhST8P4nqHjmYPH/4T4WmYE/Mo+t vhBuU6tI8N93MJydEZzJ0lRHAY+SzpOWNmwUBnKNnH0EFVWOTA0gr3NKZFthWWW6U/SS8Ir0lQ5w wPAgA7ae2V0Pyi9AjZ1thW55/Y1kl2qYAq3JKkfe2Xk+DjryxfG1r6QXnsQQF0BCxgNv8gdVb2k3 UzxujK5VlTdGzchyS0X9/gl16zOMCD9p1Pg1O3CTxmSgi2LXLIyJPigRYgBnSCln++4QLC24NiFG K0t6XcfSLPlV/oR0Fob8WEsyj5BtUGPbm31/7+OPXUhYYbN9LKx2xaqBlgtKTz98Kri+twmPOJu8 QWLdrY/ytBNcccFM/3CVMwdrry0HFRZ1n0UBkN4hFwaUegUFPUOhz1G3A55zB1YaFzOEP3SLxVWe 7K39ikWXeLo0c3SrDQwkTH2Zrc7LWsOudZtvo0DqLzZMERVlN2iAGvKjnTSojfSj1Brx94nmiQja 75LklGflGKDx4uWMO/f/kCWgcE17vtXATgDD+SF4XNLRXI799yitsBW/BDxftGR361ST4iZSjMop OMaOp+E1Mk22OmXEYPq6wGwoxuVIZU8yWFA92RkxLyVHUP+lb+g7XAzKtdAlsZJ2SiHlUXwWv2FY FkWRbOMTxQWe4Z89PvBhDc3xPo4j20iIUMy5RKerO96GR05+LrobD/AfeJl1Q3Hh3C49wEJwUxfa YVV6Njp5p+PQw/7IEU2CmDYFm197mj/5ODR0QET1DlBo6OSXQUTiBJcYulIK5/37D2veYz66KlcP +GwashhllGX9/RvhWuik3w45JFZAGBmN3oVd0CTnjOe9v4tO8CCyC0JBDCLiz7wxo827vW7Kzq10 lXivwfbliMbVMiRiW4Kg3GpdSt8vwvizMgdfHczCWgyFiytVJ1xCepySpvTsFURs9XTF+bwFER3I JVqqYU7w4/toK3h1Quvdaa4JnJRmcMMenNcS+o6SZhPHe+BQppI3TQYQtllTG8uTy0eVAvIGyL1N nL7W5QN7j+4qdBdXE= X-QQ-XMRINFO: OWPUhxQsoeAVDbp3OJHYyFg= From: Yuwen Chen To: ywen.chen@foxmail.com Cc: akpm@linux-foundation.org, axboe@kernel.dk, bgeffon@google.com, licayy@outlook.com, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, liumartin@google.com, minchan@kernel.org, richardycc@google.com, senozhatsky@chromium.org Subject: [PATCH v3] zram: Implement multi-page write-back Date: Wed, 5 Nov 2025 14:48:06 +0800 X-OQ-MSGID: <20251105064806.2693018-1-ywen.chen@foxmail.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: EFEF5160004 X-Rspamd-Server: rspam07 X-Stat-Signature: teczcxz11g7ygme4pbw6pdigri95exne X-Rspam-User: X-HE-Tag: 1762325317-304777 X-HE-Meta: U2FsdGVkX1+srTYZ3sG8qCxiAwsISqWhP6W4DG6shjwoPTyMaQd35i2FfsyXVTyrbSN55hDx7kv2OW/Gie7UHCA63qaz+y9OxXUPoiXs/PKm5JI6xB3y8DG8xRacrBU2lvIo3XUc8K3CiysTdHjRh6g/WSwwxGOLWCC9EoERdoHFbQIU6yzURV3IVO7FiBglQO4R6EE5giNGqji/tlu8ODMCWbJ3TmU+mtNNkr7tIvAN4xory5HtjcCWrMiIdCV/SHXbitjz1TQSThOcciBsRXnX9mqndOc4E5lZg1LNMDdc7oEfBwnb2XLmfdMtyRgCE8Tu9tHDNIoxZeBaca2ZYPKxSDTAlzFvDrWN/faqURZKKxOQ+NLhPV6j5jDYT/D2KbbI9iO2AB8P1XTn5YAegv7Fnl4w3RLho4MNua5fRXFM+Uk6Fxe32oD9Tnev6gOWP0PXhSjeE9dFATIiGGBBOeJdyZj5bMxHcs9PdktORzX7L8Z8fTIjQx3Gy/Qp/y6+zDfkPWLAwP07IPUF3xn3XfJ21qJ2aSKtFE24ATOuHEFbAsKqTeujeBuK9/9iIw1Az6289fpQ+UgQu6XdY88Hc2lc0XlBAvULKIbusHDLALqlG0q4WIPq16urNmeKzQmHTc7kFSAWjpIPCssJV44puhtKFxeHAhLIvd9douN5C7ZmtvMFIIMKmQZoim0943reGUBChONI0CLIIRHb0+gYpd8XAOYlYnMlNLKjKwaqqkB+xoH2P0IpZcdHuugL7AVl7N/weqglLiEZebMu48mDp1hoBz2gXw2YJd0SsrmxiM0go8cYRsH5JtvRAbPlBH778WfyQu29M5E7TWZxz7LVy7x15pp6lMOviBn9R1x0XC6+OEBTLVCnj/c/DAiO59vCLlngkLMBxHKRSabsJc10IL9+xuMPtrIBaVoRux5385ycm6Tj7s7sKqYrSpvnlPA3MdivITTDnVddVRsZxYe xUZ/eAX7 R9X/bsCoD+ovPknNumymFhGXgwCOgFzg4O/lG2jUHYMpeqUwO4GYQC23ib/7QJRnkoezQGco+IqkRGAMy0/nVn1izxCdVpzcN1dP5fgEpAnfXcGcZoK7aB5oQTYN3RYuSxqHrGqbnoIfKA5KDG3gs3bv65m7SkeYaEyHSKwnJGk/osldXyHeYk1BSS5zjL5vu4x4QKhFngPaHOW/J7Ausx3XsCeUvr2y8yxrWQMkFmL+l3uVERxYn8/r5+Zdt1WmX5XvJWAbQbQ31rFNoa7AEfh8NkilSMRfCWR9jzeLU3NBbR3k= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: For block devices, sequential write performance is significantly better than random write. Currently, zram's write-back function only supports single-page operations, which fails to leverage the sequential write advantage and leads to suboptimal performance. This patch implements multi-page batch write-back for zram to leverage sequential write performance of block devices. After applying this patch, a large number of pages being merged into batch write operations can be observed via the following test code, which effectively improves write-back performance. mount -t debugfs none /sys/kernel/debug/ echo "block:block_bio_frontmerge" >> /sys/kernel/debug/tracing/set_event echo "block:block_bio_backmerge" >> /sys/kernel/debug/tracing/set_event cat /sys/kernel/debug/tracing/trace_pipe & echo "page_indexes=1-10000" > /sys/block/zram0/writeback Signed-off-by: Yuwen Chen Reviewed-by: Fengyu Lian --- Changes in v3: - Postpone the page allocation. Changes in v2: - Rename some data structures. - Fix an exception caused by accessing a null pointer. --- drivers/block/zram/zram_drv.c | 224 ++++++++++++++++++++++++++-------- 1 file changed, 170 insertions(+), 54 deletions(-) diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c index 4f2824a..ce8fc3c 100644 --- a/drivers/block/zram/zram_drv.c +++ b/drivers/block/zram/zram_drv.c @@ -751,21 +751,131 @@ static void read_from_bdev_async(struct zram *zram, struct page *page, submit_bio(bio); } -static int zram_writeback_slots(struct zram *zram, struct zram_pp_ctl *ctl) -{ - unsigned long blk_idx = 0; - struct page *page = NULL; +enum { + /* Indicate that the request has been allocated */ + ZRAM_WB_REQUEST_ALLOCATED = 0, + + /* the request has been processed by the block device layer */ + ZRAM_WB_REQUEST_COMPLETED, +}; + +struct zram_wb_request { + struct completion *done; + unsigned long blk_idx; + struct page *page; struct zram_pp_slot *pps; struct bio_vec bio_vec; struct bio bio; - int ret = 0, err; - u32 index; + unsigned long flags; +}; - page = alloc_page(GFP_KERNEL); - if (!page) - return -ENOMEM; +static int zram_writeback_complete(struct zram *zram, struct zram_wb_request *req) +{ + u32 index = 0; + int err; - while ((pps = select_pp_slot(ctl))) { + if (!test_and_clear_bit(ZRAM_WB_REQUEST_COMPLETED, &req->flags)) + return 0; + + err = blk_status_to_errno(req->bio.bi_status); + if (err) + return err; + + index = req->pps->index; + atomic64_inc(&zram->stats.bd_writes); + zram_slot_lock(zram, index); + /* + * Same as above, we release slot lock during writeback so + * slot can change under us: slot_free() or slot_free() and + * reallocation (zram_write_page()). In both cases slot loses + * ZRAM_PP_SLOT flag. No concurrent post-processing can set + * ZRAM_PP_SLOT on such slots until current post-processing + * finishes. + */ + if (!zram_test_flag(zram, index, ZRAM_PP_SLOT)) + goto next; + + zram_free_page(zram, index); + zram_set_flag(zram, index, ZRAM_WB); + zram_set_handle(zram, index, req->blk_idx); + req->blk_idx = 0; + atomic64_inc(&zram->stats.pages_stored); + spin_lock(&zram->wb_limit_lock); + if (zram->wb_limit_enable && zram->bd_wb_limit > 0) + zram->bd_wb_limit -= 1UL << (PAGE_SHIFT - 12); + spin_unlock(&zram->wb_limit_lock); + +next: + zram_slot_unlock(zram, index); + release_pp_slot(zram, req->pps); + req->pps = NULL; + return 0; +} + +static void zram_writeback_endio(struct bio *bio) +{ + struct zram_wb_request *req = bio->bi_private; + + set_bit(ZRAM_WB_REQUEST_COMPLETED, &req->flags); + clear_bit(ZRAM_WB_REQUEST_ALLOCATED, &req->flags); + complete(req->done); +} + +static struct zram_wb_request *zram_writeback_next_request(struct zram_wb_request *pool, + int pool_cnt, int *cnt_off) +{ + struct zram_wb_request *req = NULL; + int i = 0; + + for (i = *cnt_off; i < pool_cnt + *cnt_off; i++) { + req = &pool[i % pool_cnt]; + if (!req->page) { + /* This memory should be freed by the caller. */ + req->page = alloc_page(GFP_KERNEL); + if (!req->page) + continue; + } + + if (!test_and_set_bit(ZRAM_WB_REQUEST_ALLOCATED, &req->flags)) { + *cnt_off = (i + 1) % pool_cnt; + return req; + } + } + return NULL; +} + +#define ZRAM_WB_REQ_CNT (32) +static int zram_writeback_slots(struct zram *zram, struct zram_pp_ctl *ctl) +{ + int ret = 0, err, i = 0, cnt_off = 0; + int req_pool_cnt = 0; + struct zram_wb_request req_prealloc[2] = {0}; + struct zram_wb_request *req = NULL, *req_pool = NULL; + DECLARE_COMPLETION_ONSTACK(done); + u32 index = 0; + struct blk_plug plug; + + /* allocate memory for req_pool */ + req_pool = kzalloc(sizeof(*req) * ZRAM_WB_REQ_CNT, GFP_KERNEL); + if (req_pool) { + req_pool_cnt = ZRAM_WB_REQ_CNT; + } else { + req_pool = req_prealloc; + req_pool_cnt = ARRAY_SIZE(req_prealloc); + } + + for (i = 0; i < req_pool_cnt; i++) { + req_pool[i].done = &done; + req_pool[i].flags = 0; + } + req = zram_writeback_next_request(req_pool, req_pool_cnt, &cnt_off); + if (!req) { + ret = -ENOMEM; + goto out_free_req_pool; + } + + blk_start_plug(&plug); + while ((req->pps = select_pp_slot(ctl))) { spin_lock(&zram->wb_limit_lock); if (zram->wb_limit_enable && !zram->bd_wb_limit) { spin_unlock(&zram->wb_limit_lock); @@ -774,15 +884,15 @@ static int zram_writeback_slots(struct zram *zram, struct zram_pp_ctl *ctl) } spin_unlock(&zram->wb_limit_lock); - if (!blk_idx) { - blk_idx = alloc_block_bdev(zram); - if (!blk_idx) { + if (!req->blk_idx) { + req->blk_idx = alloc_block_bdev(zram); + if (!req->blk_idx) { ret = -ENOSPC; break; } } - index = pps->index; + index = req->pps->index; zram_slot_lock(zram, index); /* * scan_slots() sets ZRAM_PP_SLOT and relases slot lock, so @@ -792,22 +902,32 @@ static int zram_writeback_slots(struct zram *zram, struct zram_pp_ctl *ctl) */ if (!zram_test_flag(zram, index, ZRAM_PP_SLOT)) goto next; - if (zram_read_from_zspool(zram, page, index)) + if (zram_read_from_zspool(zram, req->page, index)) goto next; zram_slot_unlock(zram, index); - bio_init(&bio, zram->bdev, &bio_vec, 1, + bio_init(&req->bio, zram->bdev, &req->bio_vec, 1, REQ_OP_WRITE | REQ_SYNC); - bio.bi_iter.bi_sector = blk_idx * (PAGE_SIZE >> 9); - __bio_add_page(&bio, page, PAGE_SIZE, 0); - - /* - * XXX: A single page IO would be inefficient for write - * but it would be not bad as starter. - */ - err = submit_bio_wait(&bio); + req->bio.bi_iter.bi_sector = req->blk_idx * (PAGE_SIZE >> 9); + req->bio.bi_end_io = zram_writeback_endio; + req->bio.bi_private = req; + __bio_add_page(&req->bio, req->page, PAGE_SIZE, 0); + + list_del_init(&req->pps->entry); + submit_bio(&req->bio); + + do { + req = zram_writeback_next_request(req_pool, req_pool_cnt, &cnt_off); + if (!req) { + blk_finish_plug(&plug); + wait_for_completion_io(&done); + blk_start_plug(&plug); + } + } while (!req); + err = zram_writeback_complete(zram, req); if (err) { - release_pp_slot(zram, pps); + release_pp_slot(zram, req->pps); + req->pps = NULL; /* * BIO errors are not fatal, we continue and simply * attempt to writeback the remaining objects (pages). @@ -817,43 +937,39 @@ static int zram_writeback_slots(struct zram *zram, struct zram_pp_ctl *ctl) * the most recent BIO error. */ ret = err; - continue; } + cond_resched(); + continue; - atomic64_inc(&zram->stats.bd_writes); - zram_slot_lock(zram, index); - /* - * Same as above, we release slot lock during writeback so - * slot can change under us: slot_free() or slot_free() and - * reallocation (zram_write_page()). In both cases slot loses - * ZRAM_PP_SLOT flag. No concurrent post-processing can set - * ZRAM_PP_SLOT on such slots until current post-processing - * finishes. - */ - if (!zram_test_flag(zram, index, ZRAM_PP_SLOT)) - goto next; - - zram_free_page(zram, index); - zram_set_flag(zram, index, ZRAM_WB); - zram_set_handle(zram, index, blk_idx); - blk_idx = 0; - atomic64_inc(&zram->stats.pages_stored); - spin_lock(&zram->wb_limit_lock); - if (zram->wb_limit_enable && zram->bd_wb_limit > 0) - zram->bd_wb_limit -= 1UL << (PAGE_SHIFT - 12); - spin_unlock(&zram->wb_limit_lock); next: zram_slot_unlock(zram, index); - release_pp_slot(zram, pps); - + release_pp_slot(zram, req->pps); + req->pps = NULL; cond_resched(); } + blk_finish_plug(&plug); - if (blk_idx) - free_block_bdev(zram, blk_idx); - if (page) - __free_page(page); + if (req) + clear_bit(ZRAM_WB_REQUEST_ALLOCATED, &req->flags); + for (i = 0; i < req_pool_cnt; i++) { + while (test_bit(ZRAM_WB_REQUEST_ALLOCATED, &req_pool[i].flags)) + wait_for_completion_io(&done); + err = zram_writeback_complete(zram, &req_pool[i]); + if (err) { + release_pp_slot(zram, req_pool[i].pps); + req->pps = NULL; + ret = err; + } + + if (req_pool[i].blk_idx) + free_block_bdev(zram, req_pool[i].blk_idx); + if (req_pool[i].page) + __free_page(req_pool[i].page); + } +out_free_req_pool: + if (req_pool != req_prealloc) + kfree(req_pool); return ret; } -- 2.34.1