From: Matthew Wilcox <willy@infradead.org>
To: Yosry Ahmed <yosryahmed@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Johannes Weiner <hannes@cmpxchg.org>,
Michal Hocko <mhocko@kernel.org>,
Roman Gushchin <roman.gushchin@linux.dev>,
Shakeel Butt <shakeelb@google.com>,
Muchun Song <muchun.song@linux.dev>,
cgroups@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH] mm: memcg: remove direct use of __memcg_kmem_uncharge_page
Date: Wed, 13 Dec 2023 15:01:28 +0000 [thread overview]
Message-ID: <ZXnHSPuaVW913iVZ@casper.infradead.org> (raw)
In-Reply-To: <20231213130414.353244-1-yosryahmed@google.com>
On Wed, Dec 13, 2023 at 01:04:14PM +0000, Yosry Ahmed wrote:
> memcg_kmem_uncharge_page() is an inline wrapper around
> __memcg_kmem_uncharge_page() that checks memcg_kmem_online() before
> making the function call. Internally, __memcg_kmem_uncharge_page() has a
> folio_memcg_kmem() check.
>
> The only direct user of __memcg_kmem_uncharge_page(),
> free_pages_prepare(), checks PageMemcgKmem() before calling it to avoid
> the function call if possible. Move the folio_memcg_kmem() check from
> __memcg_kmem_uncharge_page() to memcg_kmem_uncharge_page() as
> PageMemcgKmem() -- which does the same thing under the hood. Now
> free_pages_prepare() can also use memcg_kmem_uncharge_page().
I think you've just pessimised all the other places which call
memcg_kmem_uncharge_page(). It's a matter of probabilities. In
free_pages_prepare(), most of the pages being freed are not accounted
to memcg. Whereas in fork() we are absolutely certain that the pages
were accounted because we accounted them.
I think this is a bad change.
next prev parent reply other threads:[~2023-12-13 15:01 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-12-13 13:04 Yosry Ahmed
2023-12-13 14:26 ` Muchun Song
2023-12-13 15:01 ` Matthew Wilcox [this message]
2023-12-13 15:08 ` Yosry Ahmed
2023-12-13 15:38 ` Matthew Wilcox
2023-12-13 15:42 ` Yosry Ahmed
2023-12-13 16:23 ` Matthew Wilcox
2023-12-13 16:24 ` Yosry Ahmed
2023-12-13 16:27 ` Matthew Wilcox
2023-12-13 16:31 ` Yosry Ahmed
2023-12-13 20:23 ` Shakeel Butt
2023-12-13 20:27 ` Matthew Wilcox
2023-12-13 20:41 ` Shakeel Butt
2023-12-13 20:58 ` Shakeel Butt
2023-12-13 22:04 ` Yosry Ahmed
2023-12-13 22:12 ` Shakeel Butt
2023-12-13 22:15 ` Yosry Ahmed
2023-12-14 1:46 ` Roman Gushchin
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