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 X-Spam-Level: X-Spam-Status: No, score=-0.9 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id DA085C04EB9 for ; Sat, 1 Dec 2018 13:42:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9C79D20834 for ; Sat, 1 Dec 2018 13:42:00 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="CejCek3F" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9C79D20834 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=gmail.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-btrfs-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726815AbeLBAyb (ORCPT ); Sat, 1 Dec 2018 19:54:31 -0500 Received: from mail-yb1-f172.google.com ([209.85.219.172]:35584 "EHLO mail-yb1-f172.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726619AbeLBAyb (ORCPT ); Sat, 1 Dec 2018 19:54:31 -0500 Received: by mail-yb1-f172.google.com with SMTP id z2-v6so3480925ybj.2 for ; Sat, 01 Dec 2018 05:41:58 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:from:date:message-id:subject:to :content-transfer-encoding; bh=N+MaJiC6krqG6fLhf/EhmTZ5x1RvECweraeAfiBXUks=; b=CejCek3Fh5MnxPJxnKa59pvHx12KznRHyRcjSa6FyTh0IS02a0m6zp/1JgMb51b2R2 tF9SYC4YpqtPGg8sPmEs2O5Hrf3Y3nf94272G5am2YHBiGtLhmHk7MS9eqLYl9OkJ5RY aCoTK8NnqwArFn2pYNJ9USsr9a7+0/4XvK+C5wP6xa0xtdvzYfHU0LsomY7VAFlaw2Au NwahiiH0bg6QLmXIKJ0UH6E5ep2CmwqHyR23GgQKuMo+0CMr15M+rsfFtlXwfC/tZf6k HKinH5m1EVC3iC3x4nnfXBZmSYLe4xMhtdAoGEkQoP7wXPzeVm+F9qMrBjGu19REUS3n bUWA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:from:date:message-id:subject:to :content-transfer-encoding; bh=N+MaJiC6krqG6fLhf/EhmTZ5x1RvECweraeAfiBXUks=; b=k2JO1rWMlQ3uetmGIPrJqEs22Kj/GgDbk4D8v0SjhK4Yqu8KmyjC9UCAtOlfRV+uMV bfsnmM7oQ7WOI3XTYmAyrmWavOeP2JW9xk3KLe9Y4EIx5hI6gSmGjy11d5bKmYG5vBo1 E2MfdoEpFP5pQ30Ll2PqpIiFJgRq/avocHDtv18FPep9ebXEH7K5iaxYW7118ZzGaVaq wkAK2m1JS0WalORmEvZ2daGU7e9ahZMVuu7qbwQYOuUmCnsmqSCdZosoYwjgEXg808yl WVY3yMmIfak2/lyweuipuW0HSAzVGRQR6poHw9d6SZ+ZFLIj/8w/4v9tmi6sHc1nic7l 7C3A== X-Gm-Message-State: AA+aEWaxp8DT3R0BwWJhgVpk6gjsazr4jtPqOOp0IZcHz+h5HczxuOyr HkhHXWTE3KJb5lpD/7EYCxsid/QwFwpXwqAEjDJS0koo X-Google-Smtp-Source: AFSGD/XQWBGnHT3k8oHMqNJ94vKFDN3yDZes6KPdSUshf3w7gEGOlLGWF4Ph+IFPGDsKnWT72MhyM1kdQ8fQ2syQUSY= X-Received: by 2002:a25:7742:: with SMTP id s63mr3028455ybc.254.1543671718027; Sat, 01 Dec 2018 05:41:58 -0800 (PST) MIME-Version: 1.0 From: Zhengping Zhou Date: Sat, 1 Dec 2018 21:41:45 +0800 Message-ID: Subject: =?UTF-8?Q?Question_about_function_=E2=80=9Dend=5Fbio=5Fextent=5Freadpage?= =?UTF-8?Q?=E2=80=9D_in_btrfs?= To: linux-btrfs@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org Hi all: I'm wonding why we should recheck inode->i_size and zero_user_segment the page's tail which crossed the EOF, I think it's already zerofilled in function __do_readpage. function end_bio_extent_readpage: 2597 readpage_ok: 2598 if (likely(uptodate)) { 2599 loff_t i_size =3D i_size_read(inode); 2600 pgoff_t end_index =3D i_size >> PAGE_SHIFT; 2601 unsigned off; 2602 2603 /* Zero out the end if this page straddles i_size */ 2604 off =3D i_size & (PAGE_SIZE-1); 2605 if (page->index =3D=3D end_index && off) 2606 zero_user_segment(page, off, PAGE_SIZE= ); 2607 SetPageUptodate(page); 2608 } else { 2609 ClearPageUptodate(page); 2610 SetPageError(page); 2611 } 2612 unlock_page(page); 2613 offset +=3D len; There could be one situation that the file was truncated after __do_readpage be called, but I think the function =E2=80=9Dtruncate_setsize=E2=80=9D will zerofill the p= age's tail which crossed the EOF Could someone give me a hint=EF=BC=81 Thanks!