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Mon, 22 Jul 2024 19:47:18 +0000 (UTC) Message-ID: <9abf7f84-c103-4280-825c-b382edb9b8fe@redhat.com> Date: Mon, 22 Jul 2024 15:47:17 -0400 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm, memcg: cg2 memory{.swap,}.peak write handlers To: David Finkel , Roman Gushchin Cc: Muchun Song , Tejun Heo , Andrew Morton , core-services@vimeo.com, Jonathan Corbet , Michal Hocko , Shakeel Butt , Shuah Khan , Johannes Weiner , Zefan Li , cgroups@vger.kernel.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org References: <20240722151713.2724855-1-davidf@vimeo.com> <20240722151713.2724855-2-davidf@vimeo.com> Content-Language: en-US From: Waiman Long In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.0 on 10.30.177.15 X-Rspam-User: X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: F1C9340020 X-Stat-Signature: yagmn3szhm7c1jb69qggjx7dna3rosqr X-HE-Tag: 1721677649-922114 X-HE-Meta: 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 hchsy1AC Hm626gpgGnjfjjpWAAInnHqbV+SP0D5pghQxPkmuX+YuNapCqZJk4AA4SMjR5zCryPip7dU5I88o6CwhjNqFuYRb4ZqEk6YvUJy8dXrCt4FYrM3S0GG1Y0wE1r23eyL9xu/R2LL3wxdebPK+NPJJIjjk4rTIacIfoHCTKJINgZUPo5cMXGrR05Uhy3imZxHrPrZlgEjPa7NtHQDxJaxjnGjCYgrb86mCSzoklVj++AP9HzL3UjeWekyb/twb1fLBemTGSwT5hbn/owC4HU8T6mqPnmm7rwBms+bcimh/IQLQGgBDKj7FA6f2D06zIkvz4gtRF 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 7/22/24 15:30, David Finkel wrote: >>> diff --git a/mm/page_counter.c b/mm/page_counter.c >>> index db20d6452b71..40d5f4990218 100644 >>> --- a/mm/page_counter.c >>> +++ b/mm/page_counter.c >>> @@ -82,6 +82,8 @@ void page_counter_charge(struct page_counter *counter, unsigned long nr_pages) >>> */ >>> if (new > READ_ONCE(c->watermark)) >>> WRITE_ONCE(c->watermark, new); >>> + if (new > READ_ONCE(c->local_watermark)) >>> + WRITE_ONCE(c->local_watermark, new); >> Hm, can't we have a single comparison on the hot path? >> Also, we read and write c->local_watermark speculatively here, Idk if it's still >> acceptable with an ability to reset watermarks "locally". Maybe it is, but >> it definitely deserves at least a comment with an explanation. > Unfortunately, since the two watermarks may be reset at different > times I don't think we > can consolidate. > e.g. I think that if the usage peaked, dropped down a bit and then was > going back > up again when the "local_watermark" was reset, we'll continue only > bumping local_watermark, > but we don't want to touch "watermark" until we hit that watermark again. If we make page_counter_reset_watermark() reset the local_watermark as well, we can guarantee "local_watermark <= watermark" and wrap one check inside the other.         if (new > READ_ONCE(c->local_watermark)) {                 WRITE_ONCE(c->local_watermark, new);                 if (new > READ_ONCE(c->watermark))                         WRITE_ONCE(c->watermark, new);         } Cheers, Longman