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=-11.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_HELO_NONE,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 EA2CAC433B4 for ; Thu, 20 May 2021 21:59:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D010A613AC for ; Thu, 20 May 2021 21:59:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231132AbhETWAV (ORCPT ); Thu, 20 May 2021 18:00:21 -0400 Received: from mail.kernel.org ([198.145.29.99]:50868 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230270AbhETWAV (ORCPT ); Thu, 20 May 2021 18:00:21 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 4EFF861363; Thu, 20 May 2021 21:58:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1621547939; bh=cr9cjPOGjSJo1JeuAfqWdjxUrbyclymJOAah1WYzXrI=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=nGabWJgBOH/sMH49BwyB0JMvb8NafpSx8D+qzkYl5SHYciNTu6ogZ8z6wTDzs/2n2 FOsWRvxk5xwxY7dmioSDFEt8ddy9QNpZaLp0/ImqOxSFC/9vo7FkjC+Sqj2vtobIc5 8Ic7xEcBjrDVTIrBHK8C0ebaduULFkTsMIfcoQoDAFmQmGqTcJYf3e6R/ozkkugPrA 0tDF2A/SFlzgjemgNt9bp4EfcCUh2vxhwRbAQrG8c2ze2493e8G0T3JRPpe9jJd48H i+hZjd2nHj04UI91G/K1r83KmGIIHkj/bwDm/6MpKE2sPPMwMv2Dha79SaKiCylIL1 5P0wjOliBfieg== Date: Thu, 20 May 2021 14:58:58 -0700 From: "Darrick J. Wong" To: Brian Foster Cc: Matthew Wilcox , linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH v3 1/3] iomap: resched ioend completion when in non-atomic context Message-ID: <20210520215858.GZ9675@magnolia> References: <20210517171722.1266878-1-bfoster@redhat.com> <20210517171722.1266878-2-bfoster@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Tue, May 18, 2021 at 07:38:01AM -0400, Brian Foster wrote: > On Mon, May 17, 2021 at 06:54:34PM +0100, Matthew Wilcox wrote: > > On Mon, May 17, 2021 at 01:17:20PM -0400, Brian Foster wrote: > > > @@ -1084,9 +1084,12 @@ iomap_finish_ioend(struct iomap_ioend *ioend, int error) > > > next = bio->bi_private; > > > > > > /* walk each page on bio, ending page IO on them */ > > > - bio_for_each_segment_all(bv, bio, iter_all) > > > + bio_for_each_segment_all(bv, bio, iter_all) { > > > iomap_finish_page_writeback(inode, bv->bv_page, error, > > > bv->bv_len); > > > + if (!atomic) > > > + cond_resched(); > > > + } > > > > I don't know that it makes sense to check after _every_ page. I might > > go for every segment. Some users check after every thousand pages. > > > > The handful of examples I come across on a brief scan (including the > other iomap usage) have a similar pattern as used here. I don't doubt > there are others, but I think I'd prefer to have more reasoning behind > adding more code than might be necessary (i.e. do we expect additional > overhead to be measurable here?). As it is, the intent isn't so much to > check on every page as much as this just happens to be the common point > of the function to cover both long bio chains and single vector bios > with large numbers of pages. It's been a while since I waded through the macro hell to find out what cond_resched actually does, but iirc it can do some fairly heavyweight things (disable preemption, call the scheduler, rcu stuff) which is why we're supposed to be a little judicious about amortizing each call over a few thousand pages. --D > Brian >