From: Roman Gushchin <guro@fb.com>
To: Muchun Song <songmuchun@bytedance.com>
Cc: <hannes@cmpxchg.org>, <mhocko@kernel.org>,
<akpm@linux-foundation.org>, <shakeelb@google.com>,
<vdavydov.dev@gmail.com>, <linux-kernel@vger.kernel.org>,
<linux-mm@kvack.org>, <duanxiongchun@bytedance.com>,
<fam.zheng@bytedance.com>, <bsingharora@gmail.com>,
<shy828301@gmail.com>, <alexs@kernel.org>, <smuchun@gmail.com>,
<zhengqi.arch@bytedance.com>
Subject: Re: [PATCH v1 01/12] mm: memcontrol: prepare objcg API for non-kmem usage
Date: Tue, 17 Aug 2021 20:01:36 -0700 [thread overview]
Message-ID: <YRx4EM0MWSjtutPD@carbon.dhcp.thefacebook.com> (raw)
In-Reply-To: <20210814052519.86679-2-songmuchun@bytedance.com>
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().
In the long run we might wanna to eliminate CONFIG_MEMCG_KMEM completely,
so let's at least not add new dependencies.
Thanks!
next prev parent reply other threads:[~2021-08-18 3:02 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 [this message]
2021-08-20 6:44 ` Muchun Song
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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