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=-5.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 77C19C388F2 for ; Thu, 22 Oct 2020 03:47:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 098BD2237B for ; Thu, 22 Oct 2020 03:47:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2895536AbgJVDr6 (ORCPT ); Wed, 21 Oct 2020 23:47:58 -0400 Received: from szxga06-in.huawei.com ([45.249.212.32]:33328 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S2443108AbgJVDr5 (ORCPT ); Wed, 21 Oct 2020 23:47:57 -0400 Received: from DGGEMS401-HUB.china.huawei.com (unknown [172.30.72.59]) by Forcepoint Email with ESMTP id 4B21E86542CC63C75B47; Thu, 22 Oct 2020 11:47:52 +0800 (CST) Received: from [127.0.0.1] (10.143.60.252) by DGGEMS401-HUB.china.huawei.com (10.3.19.201) with Microsoft SMTP Server id 14.3.487.0; Thu, 22 Oct 2020 11:47:46 +0800 Subject: Re: [PATCH rfc 0/2] mm: cma: make cma_release() non-blocking To: Roman Gushchin CC: Andrew Morton , Zi Yan , Joonsoo Kim , Mike Kravetz , , , References: <20201016225254.3853109-1-guro@fb.com> <20201022024526.GD300658@carbon.dhcp.thefacebook.com> From: "Xiaqing (A)" Message-ID: Date: Thu, 22 Oct 2020 11:47:46 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.3.0 MIME-Version: 1.0 In-Reply-To: <20201022024526.GD300658@carbon.dhcp.thefacebook.com> Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US X-Originating-IP: [10.143.60.252] X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020/10/22 10:45, Roman Gushchin wrote: > On Thu, Oct 22, 2020 at 09:54:53AM +0800, Xiaqing (A) wrote: >> >> On 2020/10/17 6:52, Roman Gushchin wrote: >> >>> This small patchset makes cma_release() non-blocking and simplifies >>> the code in hugetlbfs, where previously we had to temporarily drop >>> hugetlb_lock around the cma_release() call. >>> >>> It should help Zi Yan on his work on 1 GB THPs: splitting a gigantic >>> THP under a memory pressure requires a cma_release() call. If it's >>> a blocking function, it complicates the already complicated code. >>> Because there are at least two use cases like this (hugetlbfs is >>> another example), I believe it's just better to make cma_release() >>> non-blocking. >>> >>> It also makes it more consistent with other memory releasing functions >>> in the kernel: most of them are non-blocking. >>> >>> >>> Roman Gushchin (2): >>> mm: cma: make cma_release() non-blocking >>> mm: hugetlb: don't drop hugetlb_lock around cma_release() call >>> >>> mm/cma.c | 51 +++++++++++++++++++++++++++++++++++++++++++++++++-- >>> mm/hugetlb.c | 6 ------ >>> 2 files changed, 49 insertions(+), 8 deletions(-) >>> >> I don't think this patch is a good idea.It transfers part or even all of the time of >> cma_release to cma_alloc, which is more concerned by performance indicators. > I'm not quite sure: if cma_alloc() is racing with cma_release(), cma_alloc() will > wait for the cma_lock mutex anyway. So we don't really transfer anything to cma_alloc(). > >> On Android phones, CPU resource competition is intense in many scenarios, >> As a result, kernel threads and workers can be scheduled only after some ticks or more. >> In this case, the performance of cma_alloc will deteriorate significantly, >> which is not good news for many services on Android. > Ok, I agree, if the cpu is heavily loaded, it might affect the total execution time. > > If we aren't going into the mutex->spinlock conversion direction (as Mike suggested), > we can address the performance concerns by introducing a cma_release_nowait() function, > so that the default cma_release() would work in the old way. > cma_release_nowait() can set an atomic flag on a cma area, which will cause following > cma_alloc()'s to flush the release queue. In this case there will be no performance > penalty unless somebody is using cma_release_nowait(). > Will it work for you? That looks good to me. Thanks! > > Thank you! > >