From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752964AbbGFRV5 (ORCPT ); Mon, 6 Jul 2015 13:21:57 -0400 Received: from mail.kernel.org ([198.145.29.136]:36635 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751364AbbGFRV4 convert rfc822-to-8bit (ORCPT ); Mon, 6 Jul 2015 13:21:56 -0400 MIME-Version: 1.0 In-Reply-To: <559A5F5A.9020703@redhat.com> References: <1436168690-32102-1-git-send-email-mlin@kernel.org> <1436168690-32102-10-git-send-email-mlin@kernel.org> <559A5F5A.9020703@redhat.com> Date: Mon, 6 Jul 2015 10:21:52 -0700 Message-ID: Subject: Re: [PATCH v5 10/11] block: remove bio_get_nr_vecs() From: Ming Lin To: Steven Whitehouse Cc: lkml , Christoph Hellwig , Jens Axboe , Kent Overstreet , Dongsu Park , Mike Snitzer , Ming Lin Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jul 6, 2015 at 3:58 AM, Steven Whitehouse wrote: > > Hi, > > > On 06/07/15 08:44, Ming Lin wrote: >> >> From: Kent Overstreet >> >> We can always fill up the bio now, no need to estimate the possible >> size based on queue parameters. > > [snip] >> >> diff --git a/fs/gfs2/lops.c b/fs/gfs2/lops.c >> index 2c1ae86..64d3116 100644 >> --- a/fs/gfs2/lops.c >> +++ b/fs/gfs2/lops.c >> @@ -261,18 +261,11 @@ void gfs2_log_flush_bio(struct gfs2_sbd *sdp, int rw) >> static struct bio *gfs2_log_alloc_bio(struct gfs2_sbd *sdp, u64 blkno) >> { >> struct super_block *sb = sdp->sd_vfs; >> - unsigned nrvecs = bio_get_nr_vecs(sb->s_bdev); >> struct bio *bio; >> BUG_ON(sdp->sd_log_bio); >> - while (1) { >> - bio = bio_alloc(GFP_NOIO, nrvecs); >> - if (likely(bio)) >> - break; >> - nrvecs = max(nrvecs/2, 1U); >> - } >> - >> + bio = bio_alloc(GFP_NOIO, BIO_MAX_PAGES); >> bio->bi_iter.bi_sector = blkno * (sb->s_blocksize >> 9); >> bio->bi_bdev = sb->s_bdev; >> bio->bi_end_io = gfs2_end_log_write; > > > When I wrote this loop I understood that bio_alloc(GFP_NOIO, x) was only guaranteed to be successful in the case x = 1, and that for x > 1, it might return NULL. Does this now mean that for x = BIO_MAX_PAGES it will be guaranteed to never return NULL in this case? Yes, it's guaranteed. https://lkml.org/lkml/2013/11/26/47 commit df2cb6daa4cbc