linux-kernel - Re: [PATCH] mm, proc: collect percpu free pages into the free pages

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Message-ID: <ed533d8b-40b7-447f-8453-e03b291340fa@huawei.com>
Date: Wed, 4 Sep 2024 14:49:20 +0800
From: mawupeng <mawupeng1@...wei.com>
To: <mhocko@...e.com>
CC: <mawupeng1@...wei.com>, <ying.huang@...el.com>,
	<akpm@...ux-foundation.org>, <mgorman@...hsingularity.net>,
	<dmaluka@...omium.org>, <liushixin2@...wei.com>,
	<wangkefeng.wang@...wei.com>, <linux-mm@...ck.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm, proc: collect percpu free pages into the free pages



On 2024/9/3 16:09, Michal Hocko wrote:
> On Tue 03-09-24 09:50:48, mawupeng wrote:
>>> Drain remote PCP may be not that expensive now after commit 4b23a68f9536
>>> ("mm/page_alloc: protect PCP lists with a spinlock").  No IPI is needed
>>> to drain the remote PCP.
>>
>> This looks really great, we can think a way to drop pcp before goto slowpath
>> before swap.
> 
> We currently drain after first unsuccessful direct reclaim run. Is that
> insufficient? 

The reason i said the drain of pcp is insufficient or expensive is based
on you comment[1] :-）. Since IPIs is not requiered since commit 4b23a68f9536
("mm/page_alloc: protect PCP lists with a spinlock"). This could be much
better.

[1]: https://lore.kernel.org/linux-mm/ZWRYZmulV0B-Jv3k@tiehlicka/

> Should we do a less aggressive draining sooner? Ideally
> restricted to cpus on the same NUMA node maybe? Do you have any specific
> workloads that would benefit from this?

Current the problem is amount the pcp, which can increase to 4.6%(24644M)
of the total 512G memory.