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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, NICE_REPLY_A,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 C7C88C433C1 for ; Wed, 24 Mar 2021 22:20:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9062561A1D for ; Wed, 24 Mar 2021 22:20:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232622AbhCXWT2 (ORCPT ); Wed, 24 Mar 2021 18:19:28 -0400 Received: from mail.kernel.org ([198.145.29.99]:49560 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231854AbhCXWTD (ORCPT ); Wed, 24 Mar 2021 18:19:03 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id AFC1E619BB; Wed, 24 Mar 2021 22:19:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1616624342; bh=J/cFCpFhojSwq/EJybyYuoGtHosmXHgSYJRRPyn/cwI=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=QXPW7evgp7NRn9Tzj3S/pY4xgA10TbD0p6Ct72fFZKKb+lRUSIXGEdxUbAnu+g5pJ 3Pf+OkhI4CxRFmQ1qHxUCAtpT75F9BFSi9pFovek2qj6sOErLCp4ZQM+elsa5bLN6k 8bipwhDSRs9wc65ACdaBgW/e2nlCEDYz47U4XlRg= Date: Wed, 24 Mar 2021 15:19:02 -0700 From: Andrew Morton To: Jens Axboe Cc: Jan Kara , mm-commits@vger.kernel.org, Matthew Wilcox Subject: Re: + mm-provide-filemap_range_needs_writeback-helper.patch added to -mm tree Message-Id: <20210324151902.171d2a295bebc4e511c7e679@linux-foundation.org> In-Reply-To: References: <20210302234347.N9evDxn__%akpm@linux-foundation.org> <9c04eafc-475d-31fc-e2cc-ea99aafd8972@kernel.dk> <20210324150218.bd9f1ebc4af58703ce001f77@linux-foundation.org> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.32; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk Reply-To: linux-kernel@vger.kernel.org List-ID: X-Mailing-List: mm-commits@vger.kernel.org On Wed, 24 Mar 2021 16:13:48 -0600 Jens Axboe wrote: > On 3/24/21 4:02 PM, Andrew Morton wrote: > > On Wed, 24 Mar 2021 13:48:08 -0600 Jens Axboe wrote: > > > >> On Tue, Mar 2, 2021 at 4:43 PM wrote: > >>> > >>> > >>> The patch titled > >>> Subject: mm: provide filemap_range_needs_writeback() helper > >>> has been added to the -mm tree. Its filename is > >>> mm-provide-filemap_range_needs_writeback-helper.patch > >> > >> Are you still planning on flushing this out for 5.12?? > > > > Oh. No, I wasn't planning on that. I saw nothing which made me think > > it was that urgent. > > Ehm ok, I think that was the plan though when we originally talked about > this series. At least that was what was in my original emails on this > topic :-) > > > What is the justification? How much performance benefit are we talking > > here? > > Well it's pretty huge, since if we return "nope can't do this > non-blocking" it'll mean that io_uring has to bump the operation to an > async threads. So CPU cost goes way up, and latencies does too. > > Problem is, we're now at -rc4, and it was my understanding that we'd get > this in for 5.12, but obviously way sooner than this. But I kind of lost > track when it went into your tree, until I started thinking about it > earlier today. While it's not the end of the world to wait for 5.13, > though the current situation does suck a lot for certain workloads. I'd be OK with sending it to Linus now, but we really should put some numbers behind "suck a lot" to justify it. And a -stable backport might be justified if the benefit is large enough, and if "certain workloads" are common enough. But with what have here, I and everyone else who considers these patches is going in blind!