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From: Chris Down <chris@chrisdown.name>
To: peterz@infradead.org
Cc: Michal Hocko <mhocko@suse.com>, Waiman Long <longman@redhat.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Vladimir Davydov <vdavydov.dev@gmail.com>,
	Jonathan Corbet <corbet@lwn.net>,
	Alexey Dobriyan <adobriyan@gmail.com>,
	Ingo Molnar <mingo@kernel.org>,
	Juri Lelli <juri.lelli@redhat.com>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
	linux-fsdevel@vger.kernel.org, cgroups@vger.kernel.org,
	linux-mm@kvack.org
Subject: Re: [RFC PATCH 0/8] memcg: Enable fine-grained per process memory control
Date: Tue, 18 Aug 2020 11:35:39 +0100	[thread overview]
Message-ID: <20200818103539.GA156577@chrisdown.name> (raw)
In-Reply-To: <20200818102616.GP2674@hirez.programming.kicks-ass.net>

peterz@infradead.org writes:
>On Tue, Aug 18, 2020 at 11:17:56AM +0100, Chris Down wrote:
>
>> I'd ask that you understand a bit more about the tradeoffs and intentions of
>> the patch before rushing in to declare its failure, considering it works
>> just fine :-)
>>
>> Clamping the maximal time allows the application to take some action to
>> remediate the situation, while still being slowed down significantly. 2
>> seconds per allocation batch is still absolutely plenty for any use case
>> I've come across. If you have evidence it isn't, then present that instead
>> of vague notions of "wrongness".
>
>There is no feedback from the freeing rate, therefore it cannot be
>correct in maintaining a maximum amount of pages.

memory.high is not about maintaining a maximum amount of pages. It's strictly 
best-effort, and the ramifications of a breach are typically fundamentally 
different than for dirty throttling.

>0.5 pages / sec is still non-zero, and if the free rate is 0, you'll
>crawl across whatever limit was set without any bounds. This is math
>101.
>
>It's true that I haven't been paying attention to mm in a while, but I
>was one of the original authors of the I/O dirty balancing, I do think I
>understand how these things work.

You're suggesting we replace a well understood, easy to reason about model with 
something non-trivially more complex, all on the back of you suggesting that 
the current approach is "wrong" without any evidence or quantification.

Peter, we're not going to throw out perfectly function memcg code simply 
because of your say so, especially when you've not asked for information or 
context about the tradeoffs involved, or presented any evidence that something 
perverse is actually happening.

Prescribing a specific solution modelled on some other code path here without 
producing evidence or measurements specific to the nuances of this particular 
endpoint is not a recipe for success.

  reply	other threads:[~2020-08-18 10:35 UTC|newest]

Thread overview: 42+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-17 14:08 Waiman Long
2020-08-17 14:08 ` [RFC PATCH 1/8] memcg: Enable fine-grained control of over memory.high action Waiman Long
2020-08-17 14:30   ` Chris Down
2020-08-17 15:38     ` Waiman Long
2020-08-17 16:11       ` Chris Down
2020-08-17 16:44   ` Shakeel Butt
2020-08-17 16:56     ` Chris Down
2020-08-18 19:12       ` Waiman Long
2020-08-18 19:14     ` Waiman Long
2020-08-17 14:08 ` [RFC PATCH 2/8] memcg, mm: Return ENOMEM or delay if memcg_over_limit Waiman Long
2020-08-17 14:08 ` [RFC PATCH 3/8] memcg: Allow the use of task RSS memory as over-high action trigger Waiman Long
2020-08-17 14:08 ` [RFC PATCH 4/8] fs/proc: Support a new procfs memctl file Waiman Long
2020-08-17 14:08 ` [RFC PATCH 5/8] memcg: Allow direct per-task memory limit checking Waiman Long
2020-08-17 14:08 ` [RFC PATCH 6/8] memcg: Introduce additional memory control slowdown if needed Waiman Long
2020-08-17 14:08 ` [RFC PATCH 7/8] memcg: Enable logging of memory control mitigation action Waiman Long
2020-08-17 14:08 ` [RFC PATCH 8/8] memcg: Add over-high action prctl() documentation Waiman Long
2020-08-17 15:26 ` [RFC PATCH 0/8] memcg: Enable fine-grained per process memory control Michal Hocko
2020-08-17 15:55   ` Waiman Long
2020-08-17 19:26     ` Michal Hocko
2020-08-18 19:20       ` Waiman Long
2020-08-18  9:14 ` peterz
2020-08-18  9:26   ` Michal Hocko
2020-08-18  9:59     ` peterz
2020-08-18 10:05       ` Michal Hocko
2020-08-18 10:18         ` peterz
2020-08-18 10:30           ` Michal Hocko
2020-08-18 10:36             ` peterz
2020-08-18 13:49           ` Johannes Weiner
2020-08-21 19:37             ` Peter Zijlstra
2020-08-24 16:58               ` Johannes Weiner
2020-09-07 11:47                 ` Chris Down
2020-09-09 11:53                 ` Michal Hocko
2020-08-18 10:17       ` Chris Down
2020-08-18 10:26         ` peterz
2020-08-18 10:35           ` Chris Down [this message]
2020-08-23  2:49         ` Waiman Long
2020-08-18  9:27   ` Chris Down
2020-08-18 10:04     ` peterz
2020-08-18 12:55       ` Matthew Wilcox
2020-08-20  6:11         ` Dave Chinner
2020-08-18 19:30     ` Waiman Long
2020-08-18 19:27   ` Waiman Long

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