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[73.219.103.14]) by smtp.gmail.com with ESMTPSA id m6sm4908913qkh.69.2021.10.13.08.58.06 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 13 Oct 2021 08:58:06 -0700 (PDT) Date: Wed, 13 Oct 2021 11:58:04 -0400 From: Kent Overstreet To: David Howells Cc: willy@infradead.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH] mm: Stop filemap_read() from grabbing a superfluous page Message-ID: References: <163360810881.1636291.17477809397516812670.stgit@warthog.procyon.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <163360810881.1636291.17477809397516812670.stgit@warthog.procyon.org.uk> X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: DD57BD000097 X-Stat-Signature: zjx1smrzj8zwpb4qmt5dqwnjqq4o7qk1 Authentication-Results: imf15.hostedemail.com; dkim=pass header.d=gmail.com header.s=20210112 header.b=LCbFYikT; dmarc=pass (policy=none) header.from=gmail.com; spf=pass (imf15.hostedemail.com: domain of kent.overstreet@gmail.com designates 209.85.160.182 as permitted sender) smtp.mailfrom=kent.overstreet@gmail.com X-HE-Tag: 1634140687-436185 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: On Thu, Oct 07, 2021 at 01:01:48PM +0100, David Howells wrote: > Under some circumstances, filemap_read() will allocate sufficient pages to > read to the end of the file, call readahead/readpages on them and copy the > data over - and then it will allocate another page at the EOF and call > readpage on that and then ignore it. This is unnecessary and a waste of > time and resources. > > filemap_read() *does* check for this, but only after it has already done > the allocation and I/O. Fix this by checking before calling > filemap_get_pages() also. > > Signed-off-by: David Howells > cc: Kent Overstreet > cc: Matthew Wilcox (Oracle) > cc: linux-mm@kvack.org > cc: linux-fsdevel@vger.kernel.org > Link: https://lore.kernel.org/r/160588481358.3465195.16552616179674485179.stgit@warthog.procyon.org.uk/ Acked-by: Kent Overstreet