linux-kernel - Re: [PATCH 1/4] memcg: use mod_node_page

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Message-ID: <2638bd96-d8cc-4733-a4ce-efdf8f223183@arm.com>
Date: Mon, 2 Feb 2026 10:18:52 +0530
From: Dev Jain <dev.jain@....com>
To: Shakeel Butt <shakeel.butt@...ux.dev>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
 Johannes Weiner <hannes@...xchg.org>, Michal Hocko <mhocko@...nel.org>,
 Roman Gushchin <roman.gushchin@...ux.dev>,
 Muchun Song <muchun.song@...ux.dev>, Harry Yoo <harry.yoo@...cle.com>,
 Qi Zheng <qi.zheng@...ux.dev>, Vlastimil Babka <vbabka@...e.cz>,
 linux-mm@...ck.org, cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
 Meta kernel team <kernel-team@...a.com>
Subject: Re: [PATCH 1/4] memcg: use mod_node_page_state to update stats


On 02/02/26 9:56 am, Shakeel Butt wrote:
> On Thu, Jan 29, 2026 at 06:35:21PM +0530, Dev Jain wrote:
>> On 11/11/25 4:50 am, Shakeel Butt wrote:
>>> The memcg stats are safe against irq (and nmi) context and thus does not
>>> require disabling irqs. However some code paths for memcg stats also
>>> update the node level stats and use irq unsafe interface and thus
>>> require the users to disable irqs. However node level stats, on
>>> architectures with HAVE_CMPXCHG_LOCAL (all major ones), has interface
>>> which does not require irq disabling. Let's move memcg stats code to
>>> start using that interface for node level stats.
>>>
>>> Signed-off-by: Shakeel Butt <shakeel.butt@...ux.dev>
>>> ---
>> Hello Shakeel,
>>
>> We are seeing a regression in micromm/munmap benchmark with this patch, on arm64 -
>> the benchmark mmmaps a lot of memory, memsets it, and measures the time taken
>> to munmap. Please see below if my understanding of this patch is correct.
> Thanks for the report. Are you seeing regression in just the benchmark
> or some real workload as well? Also how much regression are you seeing?
> I have a kernel rebot regression report [1] for this patch as well which
> says 2.6% regression and thus it was on the back-burner for now. I will
> take look at this again soon.

The munmap regression is ~24%. Haven't observed a regression in any other
benchmark yet.

>
> [1] https://lore.kernel.org/all/202512101408.af3876df-lkp@intel.com/
>