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=-6.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no 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 522BCC48BE5 for ; Tue, 22 Jun 2021 17:55:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3A8CF61358 for ; Tue, 22 Jun 2021 17:55:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232418AbhFVR6A (ORCPT ); Tue, 22 Jun 2021 13:58:00 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:55693 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232404AbhFVR57 (ORCPT ); Tue, 22 Jun 2021 13:57:59 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1624384543; 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: in-reply-to:in-reply-to:references:references; bh=vPJfqiVwirjPo+JOKJqBMtufCCULee1n+PUuD036/84=; b=eLwtkztNAZiNrE/q70K1ikpmUoZe/PUBOzW0Rky7qVfCgy0+o5C3yrrwMnIk5xJXYgbzqI 9Ym9EzM/QsY1ZWHPTwFwyljOYy4MpxQ80xuRgAQzl5SVl03uEPbE9UcQG326XbyRIuHa6t 8PxZp2egaoXscYw/We/Sj5GsTm0l1h8= 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-207-yQ7dfMfDPMONm30mH858Aw-1; Tue, 22 Jun 2021 13:55:39 -0400 X-MC-Unique: yQ7dfMfDPMONm30mH858Aw-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id BB440804140; Tue, 22 Jun 2021 17:55:37 +0000 (UTC) Received: from warthog.procyon.org.uk (ovpn-118-65.rdu2.redhat.com [10.10.118.65]) by smtp.corp.redhat.com (Postfix) with ESMTP id ABF055D9CA; Tue, 22 Jun 2021 17:55:34 +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 From: David Howells In-Reply-To: References: <3221175.1624375240@warthog.procyon.org.uk> To: Linus Torvalds Cc: dhowells@redhat.com, Matthew Wilcox , Al Viro , "Ted Ts'o" , Dave Hansen , Andrew Morton , Linux-MM , Ext4 Developers List , linux-fsdevel , Linux Kernel Mailing List Subject: Re: Do we need to unrevert "fs: do not prefault sys_write() user buffer pages"? MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <3231149.1624384533.1@warthog.procyon.org.uk> Date: Tue, 22 Jun 2021 18:55:33 +0100 Message-ID: <3231150.1624384533@warthog.procyon.org.uk> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org Linus Torvalds wrote: > End result: doing the fault_in_readable "unnecessarily" at the > beginning is likely the better optimization. It's basically free when > it's not necessary, and it avoids an extra fault (and extra > lock/unlock and retry) when it does end up faulting pages in. It may also cause the read in to happen in the background whilst write_begin is being done. David