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=-9.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 BFA84C433DF for ; Fri, 16 Oct 2020 12:49:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 71500207DE for ; Fri, 16 Oct 2020 12:49:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2407820AbgJPMtM convert rfc822-to-8bit (ORCPT ); Fri, 16 Oct 2020 08:49:12 -0400 Received: from smtp.h3c.com ([60.191.123.50]:14142 "EHLO h3cspam02-ex.h3c.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2394663AbgJPMtM (ORCPT ); Fri, 16 Oct 2020 08:49:12 -0400 Received: from DAG2EX02-BASE.srv.huawei-3com.com ([10.8.0.65]) by h3cspam02-ex.h3c.com with ESMTPS id 09GCmK77095507 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=FAIL); Fri, 16 Oct 2020 20:48:20 +0800 (GMT-8) (envelope-from tian.xianting@h3c.com) Received: from DAG2EX03-BASE.srv.huawei-3com.com (10.8.0.66) by DAG2EX02-BASE.srv.huawei-3com.com (10.8.0.65) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.1713.5; Fri, 16 Oct 2020 20:48:23 +0800 Received: from DAG2EX03-BASE.srv.huawei-3com.com ([fe80::5d18:e01c:bbbd:c074]) by DAG2EX03-BASE.srv.huawei-3com.com ([fe80::5d18:e01c:bbbd:c074%7]) with mapi id 15.01.1713.004; Fri, 16 Oct 2020 20:48:23 +0800 From: Tianxianting To: Michal Hocko CC: "akpm@linux-foundation.org" , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" Subject: RE: [PATCH] mm: vmscan: avoid a unnecessary reschedule in shrink_slab() Thread-Topic: [PATCH] mm: vmscan: avoid a unnecessary reschedule in shrink_slab() Thread-Index: AQHWo29cMaRbAMdQE0ycFn5GylDeeqmZnPOAgACJFdA= Date: Fri, 16 Oct 2020 12:48:23 +0000 Message-ID: <9a2b772b13f84bdd9517b17d8d72aa89@h3c.com> References: <20201016033952.1924-1-tian.xianting@h3c.com> <20201016120749.GG22589@dhcp22.suse.cz> In-Reply-To: <20201016120749.GG22589@dhcp22.suse.cz> Accept-Language: en-US Content-Language: zh-CN X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [10.99.141.128] x-sender-location: DAG2 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 8BIT MIME-Version: 1.0 X-DNSRBL: X-MAIL: h3cspam02-ex.h3c.com 09GCmK77095507 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Thanks, my understanding is, In shrink_slab(), do_shrink_slab() will do the real reclaim work, which will occupy current cpu and consume more cpu time, so we need to trigger a reschedule after reclaim. But if it jumps to 'out' label, that means we don't do the reclaim work at this time, it won't cause other thread getting starvation, so we don't need to call cond_resched() in this case. Is it right? -----Original Message----- From: Michal Hocko [mailto:mhocko@suse.com] Sent: Friday, October 16, 2020 8:08 PM To: tianxianting (RD) Cc: akpm@linux-foundation.org; linux-mm@kvack.org; linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm: vmscan: avoid a unnecessary reschedule in shrink_slab() On Fri 16-10-20 11:39:52, Xianting Tian wrote: > In shrink_slab(), it directly goes to 'out' label only when it can't > get the lock of shrinker_rwsew. In this case, it doesn't do the real > work of shrinking slab, so we don't need trigger a reschedule by > cond_resched(). Your changelog doesn't explain why this is not needed or undesirable. Do you see any actual problem? The point of this code is to provide a deterministic scheduling point regardless of the shrinker_rwsew. > > Signed-off-by: Xianting Tian > --- > mm/vmscan.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/mm/vmscan.c b/mm/vmscan.c index 466fc3144..676e97b28 > 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -687,8 +687,9 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid, > } > > up_read(&shrinker_rwsem); > -out: > + > cond_resched(); > +out: > return freed; > } > > -- > 2.17.1 > -- Michal Hocko SUSE Labs