From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out30-133.freemail.mail.aliyun.com (out30-133.freemail.mail.aliyun.com [115.124.30.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 41640EDD for ; Mon, 19 Feb 2024 02:34:35 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.133 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1708310079; cv=none; b=bIY0FmBYx8coZx2YzsGAh07p5P6En5VDVfq8utIC6xEAL8Mbtzv2s3bqI8IJwTKtgxtcVtGnbtGqxsG2QGG2p2YKoPo2CG3BZymdhTwcwUmz5jTbaOKz+cAW4YI4ZrSzqsamWjXYmMJGdW9zVmMpfF0tC4BgbgSvIMVheXcCT2s= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1708310079; c=relaxed/simple; bh=JeyK8A25Fachxr6Owd8b2m5jXCqZjqnuLwNUU7e3iic=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=PeAefGg3FMpRGmdImPQW0kGuZgMgW4AmxHRQreOABzfxDQ60g0Yh1ZYNuoGSMvH/LNNBZ+FvJI13M7CccgERHQu0xfS01K+khOl9NlYr0J6atebvrJuD34frVdCbhVm9oJin29ZDRKkqvpw0i6AJ1vTqkzYWQThUDHgrbqaOtLg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com; spf=pass smtp.mailfrom=linux.alibaba.com; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b=N4qwP1kb; arc=none smtp.client-ip=115.124.30.133 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b="N4qwP1kb" DKIM-Signature:v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1708310068; h=Message-ID:Date:MIME-Version:Subject:To:From:Content-Type; bh=HJJiNC7u8LJvikP1pwnY9KUsvCMk8b/lQNjyfCPmCtU=; b=N4qwP1kb5leMSFxZnRZ+RvxDa6b7M+F8CWTGkOOGVXS+ppFb+OuAACY/NPt/9ldxijncnyzqv7IeRbx4DwSwOtppIxl+QXapXz9uXPpI6zs50rSEjN8PvqulYjr4ZcxLjmr6f2YObjJT3lLIJRG17JCIDQf1DoZQ8TGDz53F0Js= X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R131e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=ay29a033018045168;MF=baolin.wang@linux.alibaba.com;NM=1;PH=DS;RN=6;SR=0;TI=SMTPD_---0W0moMY8_1708310067; Received: from 30.97.56.48(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0W0moMY8_1708310067) by smtp.aliyun-inc.com; Mon, 19 Feb 2024 10:34:28 +0800 Message-ID: <92e272d5-34e4-47f0-88ee-95b8a25ffd3d@linux.alibaba.com> Date: Mon, 19 Feb 2024 10:34:26 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 2/2] mm: compaction: update the cc->nr_migratepages when allocating or freeing the freepages To: Vlastimil Babka , akpm@linux-foundation.org, Zi Yan Cc: mgorman@techsingularity.net, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <0773058df022fa701b78f9a6dfe3c501a1a77351.1705928395.git.baolin.wang@linux.alibaba.com> <7f34e789-e01f-4929-a618-b73c04ebf4d2@suse.cz> From: Baolin Wang In-Reply-To: <7f34e789-e01f-4929-a618-b73c04ebf4d2@suse.cz> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 2024/2/12 18:32, Vlastimil Babka wrote: > On 1/22/24 14:01, Baolin Wang wrote: >> Currently we will use 'cc->nr_freepages >= cc->nr_migratepages' comparison >> to ensure that enough freepages are isolated in isolate_freepages(), however >> it just decreases the cc->nr_freepages without updating cc->nr_migratepages >> in compaction_alloc(), which will waste more CPU cycles and cause too many >> freepages to be isolated. > > Hm yeah I guess this can happen with fast_isolate_freepages() if it returns > with something but not all the freepages that are expected to be needed, and > then we get to isolate_freepages() again. Yes. > >> So we should also update the cc->nr_migratepages when allocating or freeing >> the freepages to avoid isolating excess freepages. And I can see fewer free >> pages are scanned and isolated when running thpcompact on my Arm64 server: >> k6.7 k6.7_patched >> Ops Compaction pages isolated 120692036.00 118160797.00 >> Ops Compaction migrate scanned 131210329.00 154093268.00 >> Ops Compaction free scanned 1090587971.00 1080632536.00 >> Ops Compact scan efficiency 12.03 14.26 >> >> Moreover, I did not see an obvious latency improvements, this is likely because >> isolating freepages is not the bottleneck in the thpcompact test case. >> k6.7 k6.7_patched >> Amean fault-both-1 1089.76 ( 0.00%) 1080.16 * 0.88%* >> Amean fault-both-3 1616.48 ( 0.00%) 1636.65 * -1.25%* >> Amean fault-both-5 2266.66 ( 0.00%) 2219.20 * 2.09%* >> Amean fault-both-7 2909.84 ( 0.00%) 2801.90 * 3.71%* >> Amean fault-both-12 4861.26 ( 0.00%) 4733.25 * 2.63%* >> Amean fault-both-18 7351.11 ( 0.00%) 6950.51 * 5.45%* >> Amean fault-both-24 9059.30 ( 0.00%) 9159.99 * -1.11%* >> Amean fault-both-30 10685.68 ( 0.00%) 11399.02 * -6.68%* >> >> Signed-off-by: Baolin Wang >> --- >> mm/compaction.c | 2 ++ >> 1 file changed, 2 insertions(+) >> >> diff --git a/mm/compaction.c b/mm/compaction.c >> index 066b72b3471a..6c84e3a5b32b 100644 >> --- a/mm/compaction.c >> +++ b/mm/compaction.c >> @@ -1779,6 +1779,7 @@ static struct folio *compaction_alloc(struct folio *src, unsigned long data) >> dst = list_entry(cc->freepages.next, struct folio, lru); >> list_del(&dst->lru); >> cc->nr_freepages--; >> + cc->nr_migratepages--; > > This is breaking the tracepoint TRACE_EVENT(mm_compaction_migratepages) > which does > > __entry->nr_failed = cc->nr_migratepages - nr_succeeded; > > and is called after migrate_pages() finishes, so now this will underflow. > > Probably need to get a snapshot of cc->nr_migratepages before calling > migrate_pages() and then feed that to the tracepoint instead of cc. Ah, good catch. Will fix in next version. Thanks.