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 64EF2C25B08 for ; Wed, 17 Aug 2022 13:52:10 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id A2E2C8D0003; Wed, 17 Aug 2022 09:52:09 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 9DBCB8D0001; Wed, 17 Aug 2022 09:52:09 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 8CAF88D0003; Wed, 17 Aug 2022 09:52:09 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0010.hostedemail.com [216.40.44.10]) by kanga.kvack.org (Postfix) with ESMTP id 7EE1F8D0001 for ; Wed, 17 Aug 2022 09:52:09 -0400 (EDT) Received: from smtpin28.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay06.hostedemail.com (Postfix) with ESMTP id 4B7B6ABDD9 for ; Wed, 17 Aug 2022 13:52:09 +0000 (UTC) X-FDA: 79809223578.28.6B1D077 Received: from out30-43.freemail.mail.aliyun.com (out30-43.freemail.mail.aliyun.com [115.124.30.43]) by imf15.hostedemail.com (Postfix) with ESMTP id 38088A01C8 for ; Wed, 17 Aug 2022 13:52:06 +0000 (UTC) X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R131e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=ay29a033018046050;MF=kanie@linux.alibaba.com;NM=1;PH=DS;RN=4;SR=0;TI=SMTPD_---0VMVoL-M_1660744318; Received: from localhost(mailfrom:kanie@linux.alibaba.com fp:SMTPD_---0VMVoL-M_1660744318) by smtp.aliyun-inc.com; Wed, 17 Aug 2022 21:52:03 +0800 From: Guixin Liu To: willy@infradead.org, akpm@linux-foundation.org Cc: linux-fsdevel@vger.kernel.org, linux-mm@kvack.org Subject: [RFC PATCH] mm/filemap.c: fix the timing of asignment of prev_pos Date: Wed, 17 Aug 2022 21:51:57 +0800 Message-Id: <1660744317-8183-1-git-send-email-kanie@linux.alibaba.com> X-Mailer: git-send-email 1.8.3.1 ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1660744329; a=rsa-sha256; cv=none; b=Zzhr4i1UXDxEL0zczYucSrVHmlju+FyT2o6Tp9yuP1lCi6WH3fkeSWAnQEzvfSjcMNXzOB SGlTnR8jXXNDAZHHS1la71timaVvc0mNMJBedMGW0xV2MqvQr2MdpCcqy+rwC1S2bp01KI 5ChmdFrf4KG2WgcgROe0uHJ7zWinfkY= ARC-Authentication-Results: i=1; imf15.hostedemail.com; dkim=none; spf=pass (imf15.hostedemail.com: domain of kanie@linux.alibaba.com designates 115.124.30.43 as permitted sender) smtp.mailfrom=kanie@linux.alibaba.com; dmarc=pass (policy=none) header.from=alibaba.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1660744329; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:content-type: content-transfer-encoding:in-reply-to:references; bh=1WFi0AJOix/+V67GabYyifvdqUPmH9EIUnXYqw48DW4=; b=X0IsJNMjVVfoPLSqnAchbpwdkROTzsECTO/IKhP6bxrQyDOHSK3RDU8Fjr6C0RdF3A9Yc1 T08OBwu1P+ElZmFU1RH2321/SYJodJWH8rTD+FgTFIREAy246J5NyjfaqwPZYrfwojEWFR CJi3S3crBBRFeiyXNMVnB8opFOC6EuE= Authentication-Results: imf15.hostedemail.com; dkim=none; spf=pass (imf15.hostedemail.com: domain of kanie@linux.alibaba.com designates 115.124.30.43 as permitted sender) smtp.mailfrom=kanie@linux.alibaba.com; dmarc=pass (policy=none) header.from=alibaba.com X-Rspam-User: X-Stat-Signature: wwaqi8rtqnikhou15xuia5gom38qmp6n X-Rspamd-Queue-Id: 38088A01C8 X-Rspamd-Server: rspam06 X-HE-Tag: 1660744326-232776 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: The prev_pos should be assigned before the iocb->ki_pos is incremented, so that the prev_pos is the exact location of the last visit. Fixes: 06c0444290cec ("mm/filemap.c: generic_file_buffered_read() now uses find_get_pages_contig") Signed-off-by: Guixin Liu --- Hi guys, When I`m running repetitive 4k read io which has same offset, I find that access to folio_mark_accessed is inevitable in the read process, the reason is that the prev_pos is assigned after the iocb->ki_pos is incremented, so that the prev_pos is always not equal to the position currently visited. Is this a bug that needs fixing? mm/filemap.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/filemap.c b/mm/filemap.c index 660490c..68fd987 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -2703,8 +2703,8 @@ ssize_t filemap_read(struct kiocb *iocb, struct iov_iter *iter, copied = copy_folio_to_iter(folio, offset, bytes, iter); already_read += copied; - iocb->ki_pos += copied; ra->prev_pos = iocb->ki_pos; + iocb->ki_pos += copied; if (copied < bytes) { error = -EFAULT; -- 1.8.3.1