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=-1.0 required=3.0 tests=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 54AB1C04EB8 for ; Tue, 4 Dec 2018 22:50:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 235D02082B for ; Tue, 4 Dec 2018 22:50:39 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 235D02082B Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux-foundation.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726679AbeLDWuh (ORCPT ); Tue, 4 Dec 2018 17:50:37 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:47364 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725886AbeLDWuh (ORCPT ); Tue, 4 Dec 2018 17:50:37 -0500 Received: from akpm3.svl.corp.google.com (unknown [104.133.8.65]) by mail.linuxfoundation.org (Postfix) with ESMTPSA id 548C3A47; Tue, 4 Dec 2018 22:50:36 +0000 (UTC) Date: Tue, 4 Dec 2018 14:50:34 -0800 From: Andrew Morton To: Josef Bacik Cc: kernel-team@fb.com, hannes@cmpxchg.org, linux-kernel@vger.kernel.org, tj@kernel.org, david@fromorbit.com, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, riel@redhat.com, jack@suse.cz Subject: Re: [PATCH 4/4] mm: use the cached page for filemap_fault Message-Id: <20181204145034.4b69bdea36506be45946f8c9@linux-foundation.org> In-Reply-To: <20181130195812.19536-5-josef@toxicpanda.com> References: <20181130195812.19536-1-josef@toxicpanda.com> <20181130195812.19536-5-josef@toxicpanda.com> X-Mailer: Sylpheed 3.6.0 (GTK+ 2.24.31; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 30 Nov 2018 14:58:12 -0500 Josef Bacik wrote: > If we drop the mmap_sem we have to redo the vma lookup which requires > redoing the fault handler. Chances are we will just come back to the > same page, so save this page in our vmf->cached_page and reuse it in the > next loop through the fault handler. > Is this really worthwhile? Rerunning the fault handler is rare (we hope) and a single pagecache lookup is fast. Some performance testing results would be helpful here. It's practically obligatory when claiming a performance improvement.