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=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 533A7C4320A for ; Sun, 8 Aug 2021 14:41:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 24B5460F0F for ; Sun, 8 Aug 2021 14:41:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231718AbhHHOli convert rfc822-to-8bit (ORCPT ); Sun, 8 Aug 2021 10:41:38 -0400 Received: from eu-smtp-delivery-151.mimecast.com ([185.58.85.151]:45885 "EHLO eu-smtp-delivery-151.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229923AbhHHOlh (ORCPT ); Sun, 8 Aug 2021 10:41:37 -0400 Received: from AcuMS.aculab.com (156.67.243.121 [156.67.243.121]) (Using TLS) by relay.mimecast.com with ESMTP id uk-mta-230-4gOXD3bKO7GKpbzy2TrY7g-1; Sun, 08 Aug 2021 15:41:15 +0100 X-MC-Unique: 4gOXD3bKO7GKpbzy2TrY7g-1 Received: from AcuMS.Aculab.com (fd9f:af1c:a25b:0:994c:f5c2:35d6:9b65) by AcuMS.aculab.com (fd9f:af1c:a25b:0:994c:f5c2:35d6:9b65) with Microsoft SMTP Server (TLS) id 15.0.1497.23; Sun, 8 Aug 2021 15:41:13 +0100 Received: from AcuMS.Aculab.com ([fe80::994c:f5c2:35d6:9b65]) by AcuMS.aculab.com ([fe80::994c:f5c2:35d6:9b65%12]) with mapi id 15.00.1497.023; Sun, 8 Aug 2021 15:41:13 +0100 From: David Laight To: 'Matthew Wilcox' , Pavel Begunkov CC: Alexander Viro , "linux-fsdevel@vger.kernel.org" , "linux-kernel@vger.kernel.org" Subject: RE: [PATCH] fs: optimise generic_write_check_limits() Thread-Topic: [PATCH] fs: optimise generic_write_check_limits() Thread-Index: AQHXiscVgxiDCvywqEuIzni6Qp/HSatpr+8g Date: Sun, 8 Aug 2021 14:41:13 +0000 Message-ID: <567d7e15f59a45f6ab94428261b3e473@AcuMS.aculab.com> References: In-Reply-To: Accept-Language: en-GB, en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.202.205.107] MIME-Version: 1.0 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=C51A453 smtp.mailfrom=david.laight@aculab.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: aculab.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Matthew Wilcox > Sent: 06 August 2021 14:28 > > On Fri, Aug 06, 2021 at 12:22:10PM +0100, Pavel Begunkov wrote: > > Even though ->s_maxbytes is used by generic_write_check_limits() only in > > case of O_LARGEFILE, the value is loaded unconditionally, which is heavy > > and takes 4 indirect loads. Optimise it by not touching ->s_maxbytes, > > if it's not going to be used. > > Is this "optimisation" actually worth anything? Look at how > force_o_largefile() is used. I would suggest that on the vast majority > of machines, O_LARGEFILE is always set. An option would be to only determine ->s_maxbytes when the size if larger than MAX_NON_LFS. So you'd end up with something like: if (pos >= max_size) { if (!(file->f_flags & O_LARGEFILE)) return -EFBIG; inode = file->f_mapping->host; if (pos >= inode->i_sb->s_maxbytes) return -EFBIG; } David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)