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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 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 X-Rspamd-Queue-Id: 6C402120008 X-Rspam-User: X-Stat-Signature: 4sk1gu1jg89113f3j5c61xuwiq5e8hbe X-Rspamd-Server: rspam03 X-HE-Tag: 1708310072-5797 X-HE-Meta: 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 Gz54dib0 toQcrBENQpWhEs/eF3ck7NUDSZZwickwA5Iz2bFCDaVCj5ynXUFDhr7t9aD7aF7k+7qC1Yd1cgoZjsVExNEVcVNLY/ZqlmSnzkxhux44093m+R2l5YjPwjWvkhNIn48cjX7+UH9ykPS+dpSNq79gsOLoBFo1dd//NJv8ZENbIjsIUWkWIom6guRg8qGwMftoKU3suR5rhJsFXLLmOa1KHNjS4IsCYhy0rclAAcFK6FL1oXffUjwE9cH8PQE9+Vq8tkNVwcHjz3T9pLVCHSvMDWrqXvp8j6zRsel+f/4viv3UDHFGSPvY4Np4ZqgWq0+XpE+g4F2SgV3cUYKtlR1uggI2CbF+Q18PQz7bS X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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.