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From: Shakeel Butt <>
To: Muchun Song <>
Cc: Roman Gushchin <>,
	Johannes Weiner <>,
	Michal Hocko <>,
	 Andrew Morton <>,
	Vladimir Davydov <>,
	 LKML <>,
	Linux MM <>,
	 Xiongchun duan <>
Subject: Re: [PATCH v5 5/7] mm: memcontrol: use obj_cgroup APIs to charge kmem pages
Date: Fri, 19 Mar 2021 11:27:54 -0700	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On Fri, Mar 19, 2021 at 9:39 AM Muchun Song <> wrote:
> Since Roman series "The new cgroup slab memory controller" applied. All
> slab objects are charged via the new APIs of obj_cgroup. The new APIs
> introduce a struct obj_cgroup to charge slab objects. It prevents
> long-living objects from pinning the original memory cgroup in the memory.
> But there are still some corner objects (e.g. allocations larger than
> order-1 page on SLUB) which are not charged via the new APIs. Those
> objects (include the pages which are allocated from buddy allocator
> directly) are charged as kmem pages which still hold a reference to
> the memory cgroup.
> We want to reuse the obj_cgroup APIs to charge the kmem pages.
> If we do that, we should store an object cgroup pointer to
> page->memcg_data for the kmem pages.
> Finally, page->memcg_data will have 3 different meanings.
>   1) For the slab pages, page->memcg_data points to an object cgroups
>      vector.
>   2) For the kmem pages (exclude the slab pages), page->memcg_data
>      points to an object cgroup.
>   3) For the user pages (e.g. the LRU pages), page->memcg_data points
>      to a memory cgroup.
> We do not change the behavior of page_memcg() and page_memcg_rcu().
> They are also suitable for LRU pages and kmem pages. Why?
> Because memory allocations pinning memcgs for a long time - it exists
> at a larger scale and is causing recurring problems in the real world:
> page cache doesn't get reclaimed for a long time, or is used by the
> second, third, fourth, ... instance of the same job that was restarted
> into a new cgroup every time. Unreclaimable dying cgroups pile up,
> waste memory, and make page reclaim very inefficient.
> We can convert LRU pages and most other raw memcg pins to the objcg
> direction to fix this problem, and then the page->memcg will always
> point to an object cgroup pointer. At that time, LRU pages and kmem
> pages will be treated the same. The implementation of page_memcg()
> will remove the kmem page check.
> This patch aims to charge the kmem pages by using the new APIs of
> obj_cgroup. Finally, the page->memcg_data of the kmem page points to
> an object cgroup. We can use the __page_objcg() to get the object
> cgroup associated with a kmem page. Or we can use page_memcg()
> to get the memory cgroup associated with a kmem page, but caller must
> ensure that the returned memcg won't be released (e.g. acquire the
> rcu_read_lock or css_set_lock).
> Signed-off-by: Muchun Song <>
> Acked-by: Johannes Weiner <>

Reviewed-by: Shakeel Butt <>

  reply	other threads:[~2021-03-19 18:28 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-19 16:38 [PATCH v5 0/7] Use obj_cgroup APIs to charge kmem pages Muchun Song
2021-03-19 16:38 ` [PATCH v5 1/7] mm: memcontrol: slab: fix obtain a reference to a freeing memcg Muchun Song
2021-03-19 18:26   ` Shakeel Butt
2021-03-22 14:46   ` Johannes Weiner
2021-03-23  9:18     ` [External] " Muchun Song
2021-03-22 18:17   ` Roman Gushchin
2021-03-19 16:38 ` [PATCH v5 2/7] mm: memcontrol: introduce obj_cgroup_{un}charge_pages Muchun Song
2021-03-19 16:38 ` [PATCH v5 3/7] mm: memcontrol: directly access page->memcg_data in mm/page_alloc.c Muchun Song
2021-03-19 16:38 ` [PATCH v5 4/7] mm: memcontrol: change ug->dummy_page only if memcg changed Muchun Song
2021-03-19 16:38 ` [PATCH v5 5/7] mm: memcontrol: use obj_cgroup APIs to charge kmem pages Muchun Song
2021-03-19 18:27   ` Shakeel Butt [this message]
2021-03-22 18:13   ` Roman Gushchin
2021-03-19 16:38 ` [PATCH v5 6/7] mm: memcontrol: inline __memcg_kmem_{un}charge() into obj_cgroup_{un}charge_pages() Muchun Song
2021-03-19 18:41   ` Shakeel Butt
2021-03-22 14:34   ` Johannes Weiner
2021-03-22 18:14   ` Roman Gushchin
2021-03-19 16:38 ` [PATCH v5 7/7] mm: memcontrol: move PageMemcgKmem to the scope of CONFIG_MEMCG_KMEM Muchun Song

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