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]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3B4D3C8302F for ; Tue, 1 Jul 2025 11:15:53 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id BFD396B009F; Tue, 1 Jul 2025 07:15:52 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id B868A6B00A0; Tue, 1 Jul 2025 07:15:52 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id A4F046B00A3; Tue, 1 Jul 2025 07:15:52 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id 8F4156B009F for ; Tue, 1 Jul 2025 07:15:52 -0400 (EDT) Received: from smtpin12.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay03.hostedemail.com (Postfix) with ESMTP id 33F6AB946E for ; Tue, 1 Jul 2025 11:15:52 +0000 (UTC) X-FDA: 83615440944.12.9B2C085 Received: from dggsgout11.his.huawei.com (dggsgout11.his.huawei.com [45.249.212.51]) by imf19.hostedemail.com (Postfix) with ESMTP id 3ABE21A000B for ; Tue, 1 Jul 2025 11:15:45 +0000 (UTC) Authentication-Results: imf19.hostedemail.com; spf=pass (imf19.hostedemail.com: domain of yukuai1@huaweicloud.com designates 45.249.212.51 as permitted sender) smtp.mailfrom=yukuai1@huaweicloud.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1751368550; 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:references; bh=SjlJa06Xs/e9zDCys3CI2nJzA/TFxZBD4nvkYGTBr9E=; b=RwNjOETh0420L2rNc9IOym31R1HlV1z/EMGEljfMyiUFz6jnj6m5TVEuZtymSc1ePOvcMH cZilYxvVevs7UusC9r2xkyxDsiYqMcn85ro5U6+vURIDIw+koYCvlPbRfNexAMfSBH8Fv/ myfFWIYQdp0QIYZ5qYbqmkp2UJkAJ2A= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1751368550; a=rsa-sha256; cv=none; b=lWgfLOvypINZXt0sI6ZrieNf0PTNr+D/QXEAGcXXAQXVtYp510WDqyK+5A/Mkx2/B88mkQ /JJ72YVthsycLtXxVka6Vpqd+OEi5w6QVCOqsMLPpDkiVSJcqkfDrCQ6WFmNSD5Dfa+v+o AxB+bdcCyY5Nob06atI3rltGbqJG5dc= ARC-Authentication-Results: i=1; imf19.hostedemail.com; dkim=none; dmarc=none; spf=pass (imf19.hostedemail.com: domain of yukuai1@huaweicloud.com designates 45.249.212.51 as permitted sender) smtp.mailfrom=yukuai1@huaweicloud.com Received: from mail.maildlp.com (unknown [172.19.163.216]) by dggsgout11.his.huawei.com (SkyGuard) with ESMTPS id 4bWgSH1ZtczYQtxN for ; Tue, 1 Jul 2025 19:15:43 +0800 (CST) Received: from mail02.huawei.com (unknown [10.116.40.252]) by mail.maildlp.com (Postfix) with ESMTP id 199011A01A4 for ; Tue, 1 Jul 2025 19:15:42 +0800 (CST) Received: from huaweicloud.com (unknown [10.175.104.67]) by APP3 (Coremail) with SMTP id _Ch0CgBnxyRcw2NouS89AQ--.19855S4; Tue, 01 Jul 2025 19:15:41 +0800 (CST) From: Yu Kuai To: willy@infradead.org, akpm@linux-foundation.org Cc: linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, yukuai3@huawei.com, yukuai1@huaweicloud.com, yi.zhang@huawei.com, yangerkun@huawei.com, johnny.chenyi@huawei.com Subject: [PATCH RFC] mm/readahead: improve randread performance with readahead disabled Date: Tue, 1 Jul 2025 19:08:34 +0800 Message-Id: <20250701110834.3237307-1-yukuai1@huaweicloud.com> X-Mailer: git-send-email 2.39.2 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-CM-TRANSID:_Ch0CgBnxyRcw2NouS89AQ--.19855S4 X-Coremail-Antispam: 1UD129KBjvJXoW7Kr4rWF18CrykCF47CFyUJrb_yoW8CF1fpr W3CF4xtr18XryrZrWxJa4UXr4fKFs3ZF4fJFy3J345Aw13Gr4akr97Xw4UuFW0yr1xXay2 9r4DZF9xZr4jvrJanT9S1TB71UUUUU7qnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDU0xBIdaVrnRJUUU9Y14x267AKxVW8JVW5JwAFc2x0x2IEx4CE42xK8VAvwI8IcIk0 rVWrJVCq3wAFIxvE14AKwVWUJVWUGwA2ocxC64kIII0Yj41l84x0c7CEw4AK67xGY2AK02 1l84ACjcxK6xIIjxv20xvE14v26w1j6s0DM28EF7xvwVC0I7IYx2IY6xkF7I0E14v26r4U JVWxJr1l84ACjcxK6I8E87Iv67AKxVW0oVCq3wA2z4x0Y4vEx4A2jsIEc7CjxVAFwI0_Gc CE3s1le2I262IYc4CY6c8Ij28IcVAaY2xG8wAqx4xG64xvF2IEw4CE5I8CrVC2j2WlYx0E 2Ix0cI8IcVAFwI0_Jr0_Jr4lYx0Ex4A2jsIE14v26r1j6r4UMcvjeVCFs4IE7xkEbVWUJV W8JwACjcxG0xvY0x0EwIxGrwACjI8F5VA0II8E6IAqYI8I648v4I1lFIxGxcIEc7CjxVA2 Y2ka0xkIwI1lc7CjxVAaw2AFwI0_Jw0_GFyl42xK82IYc2Ij64vIr41l4I8I3I0E4IkC6x 0Yz7v_Jr0_Gr1lx2IqxVAqx4xG67AKxVWUJVWUGwC20s026x8GjcxK67AKxVWUGVWUWwC2 zVAF1VAY17CE14v26r1q6r43MIIYrxkI7VAKI48JMIIF0xvE2Ix0cI8IcVAFwI0_Jr0_JF 4lIxAIcVC0I7IYx2IY6xkF7I0E14v26r1j6r4UMIIF0xvE42xK8VAvwI8IcIk0rVWUJVWU CwCI42IY6I8E87Iv67AKxVWUJVW8JwCI42IY6I8E87Iv6xkF7I0E14v26r4j6r4UJbIYCT nIWIevJa73UjIFyTuYvjfUonmRUUUUU X-CM-SenderInfo: 51xn3trlr6x35dzhxuhorxvhhfrp/ X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 3ABE21A000B X-Stat-Signature: yhjh5znpdxdphcfp9rz89ncscgs8rfq5 X-Rspam-User: X-HE-Tag: 1751368545-883756 X-HE-Meta: U2FsdGVkX1/ImxucgP2Vy9MYCPocHmXl7knkwdc096t+X8wH2SRX4Y+KiDkZdi4DS7o8yEsco8ajp1uS9ZHMC1kbMzr5a5Nh/rlsL6uGiU2Kwyh16Nyc1fYQ/bku0CKCl1TSeiBz7aXn2ZPikHTKoTiy6o2bIP5V3xc6wGoCdrjaAMjxrKwQ/7nbtwVMraBmUdDUD2Oz1ktsH28FIv8BbGs3urSE54QYAy/2IR4fkxtJUHQn8xXJAsDcyuaxTd+RGsl12ZE9NhaP0nc4JStA1MsSC8IaSNjqcfPs7SYsS4TpuM0lhzYKWi0FPammof8hiKzEJxP26o9x9DnRjtbwm5xwKE7laa+ujL0WjpRjxgL33o8JQ1JRNd6hdQKmgkZnSI8AhJ/Y33fWQKNbufrKKE7Nkf3JjCQ18/8CJiEa3A3ls0D8m1yocSUtfDZtLGtP1bWC1J6OsVQRXkJwgUINY3TA57WGrbt1s75aywHL4RjZhIJoGyMrMkZuCfePrmswPJ43EDuS3SwlJTUTn4rF6aGWSlkBdyX0ASwbxVoJToxIYT3bPpSOXuJfZHdzS6AV51ib40VqoVF2dR1Fi/KqWhkjubirHWwCVn7rn8LcNPiROd4VifjxDRs4kdXc/wPvxeDXLzcP5fyOQvjAHxVjDnihJpCcyqjAMYoEHtfuPlawn7aab49CwT08XCfss3qcLH/3V20siZPAFzZ1X9pXnVIKVIdYTtVvGg3orbm7N0nSJ4maYx2rIIrHJZsfVksC/d4hLJ7DSqVuPkYm2ksbmvzkfLTYlDAPgSBdBn0V/D+1GNy3/0nE7WabFqwRRgKq4pG2Zp95O82a1MINIbcwIsPyfQUcd1sAtY80kfMbzDeP22XYFNRlKkiHuW1Yzi5khzM3VVc0XndVUTE182ftsrjF92yUAPvqsVL/EEsDBFXWFRPvrRO6MwkM9963I1hqtsD6htdvXG8HU+oMelh Wv6Bfh2g NAOaAnGWyXRWaDxVsNHq3pqjRCPb0JoXQTXjCtLt8QU2rzGfHWENuGGrdeVUWnZ5kNxkl+T1cwslzdC2o59DykrAr6Q== 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: From: Yu Kuai We have a workload of random 4k-128k read on a HDD, from iostat we observed that average request size is 256k+ and bandwidth is 100MB+, this is because readahead waste lots of disk bandwidth. Hence we disable readahead and performance from user side is indeed much better(2x+), however, from iostat we observed request size is just 4k and bandwidth is just around 40MB. Then we do a simple dd test and found out if readahead is disabled, page_cache_sync_ra() will force to read one page at a time, and this really doesn't make sense because we can just issue user requested size request to disk. Fix this problem by removing the limit to read one page at a time from page_cache_sync_ra(), this way the random read workload can get better performance with readahead disabled. PS: I'm not sure if I miss anything, so this version is RFC Signed-off-by: Yu Kuai --- mm/readahead.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-) diff --git a/mm/readahead.c b/mm/readahead.c index 20d36d6b055e..1df85ccba575 100644 --- a/mm/readahead.c +++ b/mm/readahead.c @@ -561,13 +561,21 @@ void page_cache_sync_ra(struct readahead_control *ractl, * Even if readahead is disabled, issue this request as readahead * as we'll need it to satisfy the requested range. The forced * readahead will do the right thing and limit the read to just the - * requested range, which we'll set to 1 page for this case. + * requested range. */ - if (!ra->ra_pages || blk_cgroup_congested()) { + if (blk_cgroup_congested()) { if (!ractl->file) return; + /* + * If the cgroup is congested, ensure to do at least 1 page of + * readahead to make progress on the read. + */ req_count = 1; do_forced_ra = true; + } else if (!ra->ra_pages) { + if (!ractl->file) + return; + do_forced_ra = true; } /* be dumb */ -- 2.39.2