From patchwork Thu Oct 7 12:01:48 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: David Howells X-Patchwork-Id: 12541667 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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1DFDAC433EF for ; Thu, 7 Oct 2021 12:01:57 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id A794A61260 for ; Thu, 7 Oct 2021 12:01:56 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org A794A61260 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvack.org Received: by kanga.kvack.org (Postfix) id BA58D6B006C; Thu, 7 Oct 2021 08:01:55 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id B55846B0071; Thu, 7 Oct 2021 08:01:55 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id A6B8E6B0073; Thu, 7 Oct 2021 08:01:55 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0223.hostedemail.com [216.40.44.223]) by kanga.kvack.org (Postfix) with ESMTP id 965896B006C for ; Thu, 7 Oct 2021 08:01:55 -0400 (EDT) Received: from smtpin34.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id 476D332611 for ; Thu, 7 Oct 2021 12:01:55 +0000 (UTC) X-FDA: 78669502590.34.4D1E8AE Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [216.205.24.124]) by imf07.hostedemail.com (Postfix) with ESMTP id B42CC1000BA2 for ; Thu, 7 Oct 2021 12:01:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1633608114; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding; bh=Q0DHA6PLEStWhML4k30x8iHQyL0+mjBxtrjprx4sMyA=; b=KKKzN3PNW5Rnr6J+oVmHS6CGg5YGiSIlfOW7k/RkkVNFOWTztk16jUPVPDas1NCDAhM3Ei nYrkXSBd3hEF84IFO4mbfab9jikDz5iI4zoakdsieRnORIa6VxlxVaGFM8YO//yLRzTr3d n7WkFiRNXq+p8/sEta6DgGzt8ZSe+TA= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-265-3JbSJiIIPdWbNdk-BlmspA-1; Thu, 07 Oct 2021 08:01:53 -0400 X-MC-Unique: 3JbSJiIIPdWbNdk-BlmspA-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 584D5835DE3; Thu, 7 Oct 2021 12:01:51 +0000 (UTC) Received: from warthog.procyon.org.uk (unknown [10.33.36.44]) by smtp.corp.redhat.com (Postfix) with ESMTP id AC2D960C05; Thu, 7 Oct 2021 12:01:49 +0000 (UTC) Organization: Red Hat UK Ltd. Registered Address: Red Hat UK Ltd, Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SI4 1TE, United Kingdom. Registered in England and Wales under Company Registration No. 3798903 Subject: [RFC PATCH] mm: Stop filemap_read() from grabbing a superfluous page From: David Howells To: kent.overstreet@gmail.com, willy@infradead.org Cc: dhowells@redhat.com, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Date: Thu, 07 Oct 2021 13:01:48 +0100 Message-ID: <163360810881.1636291.17477809397516812670.stgit@warthog.procyon.org.uk> User-Agent: StGit/0.23 MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: B42CC1000BA2 X-Stat-Signature: h3osdmekbsro8h8kyxqsdnjiy8nepg6q Authentication-Results: imf07.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=KKKzN3PN; dmarc=pass (policy=none) header.from=redhat.com; spf=none (imf07.hostedemail.com: domain of dhowells@redhat.com has no SPF policy when checking 216.205.24.124) smtp.mailfrom=dhowells@redhat.com X-HE-Tag: 1633608114-107039 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: 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 --- mm/filemap.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/mm/filemap.c b/mm/filemap.c index dae481293b5d..c0cdc44c844e 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -2625,6 +2625,10 @@ ssize_t filemap_read(struct kiocb *iocb, struct iov_iter *iter, if ((iocb->ki_flags & IOCB_WAITQ) && already_read) iocb->ki_flags |= IOCB_NOWAIT; + isize = i_size_read(inode); + if (unlikely(iocb->ki_pos >= isize)) + goto put_pages; + error = filemap_get_pages(iocb, iter, &pvec); if (error < 0) break;