From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f54.google.com (mail-wm0-f54.google.com [74.125.82.54]) by kanga.kvack.org (Postfix) with ESMTP id 61CF1828F2 for ; Wed, 2 Mar 2016 09:09:37 -0500 (EST) Received: by mail-wm0-f54.google.com with SMTP id l68so79512224wml.1 for ; Wed, 02 Mar 2016 06:09:37 -0800 (PST) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id j187si5046643wma.69.2016.03.02.06.09.36 for (version=TLS1 cipher=AES128-SHA bits=128/128); Wed, 02 Mar 2016 06:09:36 -0800 (PST) Subject: Re: [PATCH v2 4/5] mm, kswapd: replace kswapd compaction with waking up kcompactd References: <1454938691-2197-1-git-send-email-vbabka@suse.cz> <1454938691-2197-5-git-send-email-vbabka@suse.cz> <20160302063322.GB32695@js1304-P5Q-DELUXE> <56D6BACB.7060005@suse.cz> From: Vlastimil Babka Message-ID: <56D6F41D.9080107@suse.cz> Date: Wed, 2 Mar 2016 15:09:33 +0100 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Joonsoo Kim Cc: Joonsoo Kim , Linux Memory Management List , Andrew Morton , LKML , Andrea Arcangeli , "Kirill A. Shutemov" , Rik van Riel , Mel Gorman , David Rientjes , Michal Hocko , Johannes Weiner On 03/02/2016 02:57 PM, Joonsoo Kim wrote: > 2016-03-02 19:04 GMT+09:00 Vlastimil Babka : >> On 03/02/2016 07:33 AM, Joonsoo Kim wrote: >>> >>> >>> Why you did the test with THP? THP interferes result of main test so >>> it would be better not to enable it. >> >> >> Hmm I've always left it enabled. It makes for a more realistic interference >> and would also show unintended regressions in that closely related area. > > But, it makes review hard because complex analysis is needed to > understand the result. > > Following is the example. > > "The compaction stalls > (direct compaction) in the interfering kernel builds (probably THP's) also > decreased somewhat to kcompactd activity, yet THP alloc successes improved a > bit." > > So, why do we need this comment to understand effect of this patch? If you did > a test without THP, it would not be necessary. I see. Next time I'll do a run with THP disabled. >>> And, this patch increased compaction activity (10 times for migrate >>> scanned) >>> may be due to resetting skip block information. >> >> >> Note that kswapd compaction activity was completely non-existent for reasons >> outlined in the changelog. >>> Isn't is better to disable it >>> for this patch to work as similar as possible that kswapd does and >>> re-enable it >>> on next patch? If something goes bad, it can simply be reverted. >>> >>> Look like it is even not mentioned in the description. >> >> >> Yeah skip block information is discussed in the next patch, which mentions >> that it's being reset and why. I think it makes more sense, as when kswapd > > Yes, I know. > What I'd like to say here is that you need to care current_is_kswapd() in > this patch. This patch unintentionally change the back ground compaction thread > behaviour to restart compaction by every 64 trials because calling > curret_is_kswapd() > by kcompactd would return false and is treated as direct reclaim. Oh, you mean this path to reset the skip bits. I see. But if skip bits are already reset by kswapd when waking kcompactd, then effect of another (rare) reset in kcompactd itself will be minimal? > Result of patch 4 > and patch 5 would be same. It's certainly possible to fold patch 5 into 4. I posted them separately mainly to make review more feasible. But the differences in results are already quite small. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org