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=-19.2 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT 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 0944FC49EA3 for ; Mon, 14 Jun 2021 12:23:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E832F61241 for ; Mon, 14 Jun 2021 12:23:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233030AbhFNMZd (ORCPT ); Mon, 14 Jun 2021 08:25:33 -0400 Received: from mail.kernel.org ([198.145.29.99]:33022 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233406AbhFNMZb (ORCPT ); Mon, 14 Jun 2021 08:25:31 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id A030761002; Mon, 14 Jun 2021 12:23:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1623673409; bh=NNFtUoSA3BPcLcUKCIoPYr9H10iOagQu2r27xzwPfqw=; h=From:To:Cc:Subject:Date:From; b=WLSK/33Ui8dPEws53qEcsU4oPmAXP14BqdVJQlekSLVciJd6c+zLmlaOFPSVORT0k M4HCx4gRvnIv7aRVFqpUNa6Vu2iqBipFvwmB6pdgJzOLe6XWg6Ff0sixAJLPglr++0 HsctlMKmOdjmrpWGYKlmaolEjhXJIli6Ket4szdTsqeDAGo2DrTXU0LRTBWB9cOJaD FfT+OAM13jM12Yr93lQseVVWgdFq0GHgmFBd4B05YHcmYF9XHq0GOt+A9urv9nIQMQ Acms8h8ECDE+t0wDxbA/K6IIot/q2Ca8LxsA7mDsUZFOFtSiuUk0o1GI2oePma2Me8 vao6FrkY9XfXQ== From: Jeff Layton To: dhowells@redhat.com Cc: linux-cachefs@redhat.com, idryomov@gmail.com, willy@infradead.org, pfmeec@rit.edu, ceph-devel@vger.kernel.org, Andrew W Elble Subject: [PATCH v2] netfs: fix test for whether we can skip read when writing beyond EOF Date: Mon, 14 Jun 2021 08:23:27 -0400 Message-Id: <20210614122327.8332-1-jlayton@kernel.org> X-Mailer: git-send-email 2.31.1 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: ceph-devel@vger.kernel.org It's not sufficient to skip reading when the pos is beyond the EOF. There may be data at the head of the page that we need to fill in before the write. Add a new helper function that corrects and clarifies the logic of when we can skip reads, and have it only zero out the part of the page that won't have data copied in for the write. Finally, don't set the page Uptodate after zeroing. It's not up to date since the write data won't have been copied in yet. Fixes: e1b1240c1ff5f ("netfs: Add write_begin helper") Reported-by: Andrew W Elble Signed-off-by: Jeff Layton --- fs/netfs/read_helper.c | 47 +++++++++++++++++++++++++++++++----------- 1 file changed, 35 insertions(+), 12 deletions(-) v2: - rename new helper with netfs_* prefix - return early for full page writes - no need to calculate index to see if write is beyond last page - no need to special case i_size == 0 diff --git a/fs/netfs/read_helper.c b/fs/netfs/read_helper.c index 725614625ed4..489ab54da062 100644 --- a/fs/netfs/read_helper.c +++ b/fs/netfs/read_helper.c @@ -1011,12 +1011,42 @@ int netfs_readpage(struct file *file, } EXPORT_SYMBOL(netfs_readpage); -static void netfs_clear_thp(struct page *page) +/** + * prep_noread_page - prep a page for writing without reading first + * @page: page being prepared + * @pos: starting position for the write + * @len: length of write + * + * In some cases, write_begin doesn't need to read at all: + * - full page write + * - write that lies in a page that is completely beyond EOF + * - write that covers the the page from start to EOF or beyond it + * + * If any of these criteria are met, then zero out the unwritten parts + * of the page and return true. Otherwise, return false. + */ +static bool netfs_prep_noread_page(struct page *page, loff_t pos, size_t len) { - unsigned int i; + struct inode *inode = page->mapping->host; + loff_t i_size = i_size_read(inode); + size_t offset = offset_in_page(pos); + + /* full page write -- no need to zero anything */ + if (offset == 0 && len >= thp_size(page)) + return true; + + /* pos beyond last page in the file */ + if (pos - offset >= i_size) + goto zero_out; + + /* write that covers the whole page from start to EOF or beyond it */ + if (offset == 0 && (pos + len) >= i_size) + goto zero_out; - for (i = 0; i < thp_nr_pages(page); i++) - clear_highpage(page + i); + return false; +zero_out: + zero_user_segments(page, 0, offset, offset + len, thp_size(page)); + return true; } /** @@ -1061,8 +1091,6 @@ int netfs_write_begin(struct file *file, struct address_space *mapping, struct inode *inode = file_inode(file); unsigned int debug_index = 0; pgoff_t index = pos >> PAGE_SHIFT; - int pos_in_page = pos & ~PAGE_MASK; - loff_t size; int ret; DEFINE_READAHEAD(ractl, file, NULL, mapping, index); @@ -1090,13 +1118,8 @@ int netfs_write_begin(struct file *file, struct address_space *mapping, * within the cache granule containing the EOF, in which case we need * to preload the granule. */ - size = i_size_read(inode); if (!ops->is_cache_enabled(inode) && - ((pos_in_page == 0 && len == thp_size(page)) || - (pos >= size) || - (pos_in_page == 0 && (pos + len) >= size))) { - netfs_clear_thp(page); - SetPageUptodate(page); + netfs_prep_noread_page(page, pos, len)) { netfs_stat(&netfs_n_rh_write_zskip); goto have_page_no_wait; } -- 2.31.1