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From: Muchun Song <songmuchun@bytedance.com>
To: Roman Gushchin <guro@fb.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>,
	Michal Hocko <mhocko@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Shakeel Butt <shakeelb@google.com>,
	Vladimir Davydov <vdavydov.dev@gmail.com>,
	LKML <linux-kernel@vger.kernel.org>,
	Linux Memory Management List <linux-mm@kvack.org>,
	Xiongchun duan <duanxiongchun@bytedance.com>,
	fam.zheng@bytedance.com, "Singh, Balbir" <bsingharora@gmail.com>,
	Yang Shi <shy828301@gmail.com>, Alex Shi <alexs@kernel.org>,
	Muchun Song <smuchun@gmail.com>,
	Qi Zheng <zhengqi.arch@bytedance.com>
Subject: Re: [PATCH v1 01/12] mm: memcontrol: prepare objcg API for non-kmem usage
Date: Fri, 20 Aug 2021 14:44:08 +0800	[thread overview]
Message-ID: <CAMZfGtWfEMvDekoZEktgOfLvLG1i5m=J+XWj5=W3=W+D9-xPgg@mail.gmail.com> (raw)
In-Reply-To: <YRx4EM0MWSjtutPD@carbon.dhcp.thefacebook.com>

On Wed, Aug 18, 2021 at 11:01 AM Roman Gushchin <guro@fb.com> wrote:
>
> On Sat, Aug 14, 2021 at 01:25:08PM +0800, Muchun Song wrote:
> > Pagecache pages are charged at the allocation time and holding a
> > reference to the original memory cgroup until being reclaimed.
> > Depending on the memory pressure, specific patterns of the page
> > sharing between different cgroups and the cgroup creation and
> > destruction rates, a large number of dying memory cgroups can be
> > pinned by pagecache pages. It makes the page reclaim less efficient
> > and wastes memory.
> >
> > 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.
> >
> > Therefore, the infrastructure of objcg no longer only serves
> > CONFIG_MEMCG_KMEM. In this patch, we move the infrastructure of the
> > objcg out of the scope of the CONFIG_MEMCG_KMEM so that the LRU pages
> > can reuse it to charge pages.
> >
> > We know that the LRU pages are not accounted at the root level. But
> > the page->memcg_data points to the root_mem_cgroup. So the
> > page->memcg_data of the LRU pages always points to a valid pointer.
> > But the root_mem_cgroup dose not have an object cgroup. If we use
> > obj_cgroup APIs to charge the LRU pages, we should set the
> > page->memcg_data to a root object cgroup. So we also allocate an
> > object cgroup for the root_mem_cgroup.
> >
> > Signed-off-by: Muchun Song <songmuchun@bytedance.com>
>
> I like the "move objcg stuff to memcg/css level" part.
>
> I'm less convinced about making byte-sized charging kmem-specific
> (both naming and #ifdef CONFIG_MEMCG_KMEM). Do we really win a lot?
>
> I understand why we might wanna compile out some checks from the
> hot allocation path, but few bytes in struct objcg will not make a big
> difference, as well as few lines of code in cgroup creation/removal paths.
>
> Also it might be useful for byte-sized accounting outside kmem, e.g. zswap.
> So, I'd remove this dependency and rename to something like
> obj_cgroup_release_bytes().

Got it. I'll do that in the next version. Thanks for your suggestions.

>
> In the long run we might wanna to eliminate CONFIG_MEMCG_KMEM completely,
> so let's at least not add new dependencies.

Got it.

>
> Thanks!

  reply	other threads:[~2021-08-20  6:44 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-14  5:25 [PATCH v1 00/12] Use obj_cgroup APIs to charge the LRU pages Muchun Song
2021-08-14  5:25 ` [PATCH v1 01/12] mm: memcontrol: prepare objcg API for non-kmem usage Muchun Song
2021-08-14 22:23   ` kernel test robot
2021-08-18  3:01   ` Roman Gushchin
2021-08-20  6:44     ` Muchun Song [this message]
2021-08-14  5:25 ` [PATCH v1 02/12] mm: memcontrol: introduce compact_folio_lruvec_lock_irqsave Muchun Song
2021-08-14  5:25 ` [PATCH v1 03/12] mm: memcontrol: make lruvec lock safe when LRU pages are reparented Muchun Song
2021-08-18  3:18   ` Roman Gushchin
2021-08-18  4:28     ` Muchun Song
2021-08-18  4:47       ` Roman Gushchin
2021-08-14  5:25 ` [PATCH v1 04/12] mm: vmscan: rework move_pages_to_lru() Muchun Song
2021-08-14  5:25 ` [PATCH v1 05/12] mm: thp: introduce folio_split_queue_lock{_irqsave}() Muchun Song
2021-08-14  8:22   ` kernel test robot
2021-08-14 10:38   ` kernel test robot
2021-08-14  5:25 ` [PATCH v1 06/12] mm: thp: make split queue lock safe when LRU pages are reparented Muchun Song
2021-08-14  5:25 ` [PATCH v1 07/12] mm: memcontrol: make all the callers of {folio,page}_memcg() safe Muchun Song
2021-08-14  5:25 ` [PATCH v1 08/12] mm: memcontrol: introduce memcg_reparent_ops Muchun Song
2021-08-14  5:25 ` [PATCH v1 09/12] mm: memcontrol: use obj_cgroup APIs to charge the LRU pages Muchun Song
2021-08-14 14:08   ` kernel test robot
2021-08-14  5:25 ` [PATCH v1 10/12] mm: memcontrol: rename {un}lock_page_memcg() to {un}lock_page_objcg() Muchun Song
2021-08-14  5:25 ` [PATCH v1 11/12] mm: lru: add VM_BUG_ON_FOLIO to lru maintenance function Muchun Song
2021-08-14  5:25 ` [PATCH v1 12/12] mm: lru: use lruvec lock to serialize memcg changes Muchun Song

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