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 3E02CCCF9F8 for ; Wed, 5 Nov 2025 03:34:28 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id EFA368E0005; Tue, 4 Nov 2025 22:34:27 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id ED1E98E0002; Tue, 4 Nov 2025 22:34:27 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id DE7E78E0005; Tue, 4 Nov 2025 22:34:27 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id CDB3F8E0002 for ; Tue, 4 Nov 2025 22:34:27 -0500 (EST) Received: from smtpin08.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay09.hostedemail.com (Postfix) with ESMTP id 783C485E28 for ; Wed, 5 Nov 2025 03:34:27 +0000 (UTC) X-FDA: 84075135774.08.BDE5727 Received: from xmbghk7.mail.qq.com (xmbghk7.mail.qq.com [43.163.128.44]) by imf24.hostedemail.com (Postfix) with ESMTP id D2081180002 for ; Wed, 5 Nov 2025 03:34:24 +0000 (UTC) Authentication-Results: imf24.hostedemail.com; dkim=pass header.d=foxmail.com header.s=s201512 header.b=uCiNOlm8; dmarc=pass (policy=none) header.from=foxmail.com; spf=pass (imf24.hostedemail.com: domain of ywen.chen@foxmail.com designates 43.163.128.44 as permitted sender) smtp.mailfrom=ywen.chen@foxmail.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1762313665; a=rsa-sha256; cv=none; b=jTz4bFvvVRxxqbUiSS7SkhDVI+5j4IbRMABoFfh3zn0292k4G6dYDjivfR14VtaGXXdhZ1 Fy0hRRfblkTEO4minP1YOe1gwPGJU4WNLsUjpSFY3WbO2SqgIhCBFGvFBxXoBvh7nhA7Tr gt/XcSWgjyO3Ab8dCSyJs6cAThIwN9c= ARC-Authentication-Results: i=1; imf24.hostedemail.com; dkim=pass header.d=foxmail.com header.s=s201512 header.b=uCiNOlm8; dmarc=pass (policy=none) header.from=foxmail.com; spf=pass (imf24.hostedemail.com: domain of ywen.chen@foxmail.com designates 43.163.128.44 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=1762313665; 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=cCZd4BWtWwDfl8jPRQWP6rxG9i/adWQOFxkaWuBxQ80=; b=PskXeWFYHqYnJDxk5A4+sYJuj2lup3pq1OU/9iWPT+q7siXSoQKpOSJlQngUHeQcKemBth dAoGzIOysLz2ieZ+DsbtEU6Pe5+WYjiidWmEZMuTqLeDMMi5u5x0Tvm9R8DmDF+c3e5Ykk dShNHyPsZ9sSl6AXFg9/1AFHHXiEOzg= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=foxmail.com; s=s201512; t=1762313661; bh=cCZd4BWtWwDfl8jPRQWP6rxG9i/adWQOFxkaWuBxQ80=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=uCiNOlm8H5zBRKhnzETUok+8nIzaR86r5ELxo2FYWHDBoowjBtdrehGgTx+62ADA+ 18X3LzbIdtBsbHHBgIbyWEDemhvtkgd5rAPb30YvFEJqeeU8A6gUBtdf1QNX6s8C4z 8yhgQ1Z5GxgPNjbSqPwiO17aBeMnmaImMMFHTY84= Received: from meizu-Precision-3660.meizu.com ([14.21.33.152]) by newxmesmtplogicsvrszb20-0.qq.com (NewEsmtp) with SMTP id 87A08658; Wed, 05 Nov 2025 11:33:58 +0800 X-QQ-mid: xmsmtpt1762313638tn1vfqyw8 Message-ID: X-QQ-XMAILINFO: MBHEkxMsYPCYTvJTZVsRQ0l7cF1jmGmoPlPY6CdIxHI55vQxpPE6YJ8jycAyKl /vbrYNpvnzpz4ClZbCoCg4CZfwM81XGPvmJ03wj6srDnWSfQKHQfF2fU7HRjAnIoHePjrWjpG8LO zdR5RMV0CAXduPwW+PHmlHUKhmzoSx+qxeWQxHBGWALlmxYMMDV2T3iNEL0NsN9mDDllbKqHHbvZ dHix8jdK1nT1oEApErew9iW9QpxqUrLPq4fh5iaoP1A1XFX50p6/DPtuOkxjyK4awxRCdesi00Wc yRWIWuWrqruxi6tGJo61VaX8bKbX3Z6k2LqXtZqav6vWwzU/Lf5Zkbrg+fxu21iYPsvlwN1//bHb eyrRx+4cywi6IijkmUgWF1mV1ANTCGygQtacOqxiAt1NMqUNtP4mgcV7My1CGhfsbAFl0PJNOtrs 5dSxLgsTimsCg8QQuOvpBUxrKw5OEH32Rd2bg1ihKdEw/cA2dDNSxSSyt4w9QyXIEDS6nIZ8ggHt jtxd5JN204gFiqdlPgzRkrtcKiwwY2lf/Ta72bdsqjsUHFqvSNl+ceyxVAn2jlpqlUXjMmBioH9g KVGeq+NclBPdco8Go+NO0qFwxNCKHqIv6VSjuKVC1oXCFPtljamV/jgHIyVwvRtUfNKA9/ptnf9Y cPJi9g9Teu541XDd0YXaVsKOD8X+yh5DbVdcM86aKyhrqLGom1+L6QJwmIa+1E5tznHL8fSi5Uc0 4Ic8/iZlJrNT5F4mvCwBrdI+Dk8EFgc5LE2ehhVg9zBFD4jS39/8+IalqELR3SPLazXeov6CATmu VsLKuYjy6Wm7GqJjT/LRdzmWPobgGxExYdliiVBab6LS+MfzqDpuRXfJTfJY6f9fjWsU2UEQtjIO EDjf5kFdpS9EFDVwmGiSnUJ8CFxpSI1qioceCMAlGUohxBp9hYeTmQpDZxdIhAfkxMpiZCf0YsvW mAp7Y+QNz2cQK2VM3utH4QBl7Lj/NDPeSMhtjvp9RDJzSrWTQhYI6lefbFoBLHMCYu9Y1ZyjI9gU TYZi4ZclddkNz9ZvlYtXXx6h+65cfY34K9Il47gOdGuLwwDte0jVO3vu6JBLMkwY0gIHkhhw== X-QQ-XMRINFO: NyFYKkN4Ny6FSmKK/uo/jdU= From: Yuwen Chen To: ywen.chen@foxmail.com Cc: richardycc@google.com, axboe@kernel.dk, licayy@outlook.com, linux-kernel@vger.kernel.org, minchan@kernel.org, senozhatsky@chromium.org, akpm@linux-foundation.org, bgeffon@google.com, linux-block@vger.kernel.org, linux-mm@kvack.org, liumartin@google.com Subject: [PATCH v2] zram: Implement multi-page write-back Date: Wed, 5 Nov 2025 11:33:56 +0800 X-OQ-MSGID: <20251105033356.2682072-1-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-Server: rspam06 X-Rspamd-Queue-Id: D2081180002 X-Stat-Signature: 7wtmqqb5e7id3ogsfssdi6owhhqo9mf3 X-Rspam-User: X-HE-Tag: 1762313664-225708 X-HE-Meta: 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 5OHh0WOS PsP6NYwWqDzkTFx+aqokWkKXL3aC6yuuCNnXjieMHIRT1jQfV/osAfqBxK0HGb6C77unVmWU2b56+Sew3VJSmGq9ay85bvNBHKwELsqJ5vW9aq9Qw8C2qe1DC1U+fbYf6f9CrB/8H/9h/8g9e+Wvj96SOCc9axNZZ5cHhKEiP/NpqSZqybiFq/DgSUlJuChvgFQZqRtFLT6K7HFIFGseqX27v1oV2//qxlSZW42dCD8+SZ4vM0z3eBA8BfI/2bbLdFSPoZna+SgV2/CqsQgLMxGTwmgti9wgN02lMyRIw63rLoiE= 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 v2: - Rename some data structures. - Fix an exception caused by accessing a null pointer. --- drivers/block/zram/zram_drv.c | 223 ++++++++++++++++++++++++++-------- 1 file changed, 169 insertions(+), 54 deletions(-) diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c index 4f2824a..d2bd091 100644 --- a/drivers/block/zram/zram_drv.c +++ b/drivers/block/zram/zram_drv.c @@ -751,21 +751,130 @@ 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) + 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, 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_pool[i].page = alloc_page(GFP_KERNEL); + if (req_pool[i].page) + req = &req_pool[i]; + } + if (!req) { + ret = -ENOMEM; + goto out_free_req_pool; + } + set_bit(ZRAM_WB_REQUEST_ALLOCATED, &req->flags); + + 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 +883,15 @@ 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 +901,32 @@ 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, &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 +936,39 @@ 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