From: Roman Gushchin <guro@fb.com>
To: Michal Hocko <mhocko@kernel.org>
Cc: "linux-mm@kvack.org" <linux-mm@kvack.org>,
Johannes Weiner <hannes@cmpxchg.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Kernel Team <Kernel-team@fb.com>,
"Shakeel Butt" <shakeelb@google.com>,
Vladimir Davydov <vdavydov.dev@gmail.com>,
"Waiman Long" <longman@redhat.com>,
Christoph Lameter <cl@linux.com>
Subject: Re: [PATCH 00/16] The new slab memory controller
Date: Tue, 22 Oct 2019 15:59:06 +0000 [thread overview]
Message-ID: <20191022155901.GB21381@tower.DHCP.thefacebook.com> (raw)
In-Reply-To: <20191022133148.GP9379@dhcp22.suse.cz>
On Tue, Oct 22, 2019 at 03:31:48PM +0200, Michal Hocko wrote:
> On Thu 17-10-19 17:28:04, Roman Gushchin wrote:
> > This patchset provides a new implementation of the slab memory controller,
> > which aims to reach a much better slab utilization by sharing slab pages
> > between multiple memory cgroups. Below is the short description of the new
> > design (more details in commit messages).
> >
> > Accounting is performed per-object instead of per-page. Slab-related
> > vmstat counters are converted to bytes. Charging is performed on page-basis,
> > with rounding up and remembering leftovers.
> >
> > Memcg ownership data is stored in a per-slab-page vector: for each slab page
> > a vector of corresponding size is allocated. To keep slab memory reparenting
> > working, instead of saving a pointer to the memory cgroup directly an
> > intermediate object is used. It's simply a pointer to a memcg (which can be
> > easily changed to the parent) with a built-in reference counter. This scheme
> > allows to reparent all allocated objects without walking them over and changing
> > memcg pointer to the parent.
> >
> > Instead of creating an individual set of kmem_caches for each memory cgroup,
> > two global sets are used: the root set for non-accounted and root-cgroup
> > allocations and the second set for all other allocations. This allows to
> > simplify the lifetime management of individual kmem_caches: they are destroyed
> > with root counterparts. It allows to remove a good amount of code and make
> > things generally simpler.
>
> What is the performance impact?
As I wrote, so far we haven't found any regression on any real world workload.
Of course, it's pretty easy to come up with a synthetic test which will show
some performance hit: e.g. allocate and free a large number of objects from a
single cache from a single cgroup. The reason is simple: stats and accounting
are more precise, so it requires more work. But I don't think it's a real
problem.
On the other hand I expect to see some positive effects from the significantly
reduced number of unmovable pages: memory fragmentation should become lower.
And all kernel objects will reside on a smaller number of pages, so we can
expect a better cache utilization.
> Also what is the effect on the memory
> reclaim side and the isolation. I would expect that mixing objects from
> different cgroups would have a negative/unpredictable impact on the
> memcg slab shrinking.
Slab shrinking is already working on per-object basis, so no changes here.
Quite opposite: now the freed space can be reused by other cgroups, where
previously it was often a useless operation, as nobody can reuse the space
unless all objects will be freed and the page can be returned to the page
allocator.
Thanks!
next prev parent reply other threads:[~2019-10-22 15:59 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-18 0:28 [PATCH 00/16] The new slab memory controller Roman Gushchin
2019-10-18 0:28 ` [PATCH 01/16] mm: memcg: introduce mem_cgroup_ptr Roman Gushchin
2019-10-18 0:28 ` [PATCH 02/16] mm: vmstat: use s32 for vm_node_stat_diff in struct per_cpu_nodestat Roman Gushchin
2019-10-20 22:44 ` Christopher Lameter
2019-10-21 1:15 ` Roman Gushchin
2019-10-21 18:09 ` Christopher Lameter
2019-10-20 22:51 ` Christopher Lameter
2019-10-21 1:21 ` Roman Gushchin
2019-10-18 0:28 ` [PATCH 03/16] mm: vmstat: convert slab vmstat counter to bytes Roman Gushchin
2019-10-18 0:28 ` [PATCH 04/16] mm: memcg/slab: allocate space for memcg ownership data for non-root slabs Roman Gushchin
2019-10-18 0:28 ` [PATCH 05/16] mm: slub: implement SLUB version of obj_to_index() Roman Gushchin
2019-10-18 0:28 ` [PATCH 06/16] mm: memcg/slab: save memcg ownership data for non-root slab objects Roman Gushchin
2019-10-18 0:28 ` [PATCH 07/16] mm: memcg: move memcg_kmem_bypass() to memcontrol.h Roman Gushchin
2019-10-18 0:28 ` [PATCH 08/16] mm: memcg: introduce __mod_lruvec_memcg_state() Roman Gushchin
2019-10-18 0:28 ` [PATCH 09/16] mm: memcg/slab: charge individual slab objects instead of pages Roman Gushchin
2019-10-25 19:41 ` Johannes Weiner
2019-10-25 20:00 ` Roman Gushchin
2019-10-25 20:52 ` Johannes Weiner
2019-10-31 1:52 ` Roman Gushchin
2019-10-31 14:23 ` Johannes Weiner
2019-10-31 14:41 ` Johannes Weiner
2019-10-31 15:07 ` Roman Gushchin
2019-10-31 18:50 ` Johannes Weiner
2019-10-18 0:28 ` [PATCH 10/16] mm: memcg: move get_mem_cgroup_from_current() to memcontrol.h Roman Gushchin
2019-10-18 0:28 ` [PATCH 11/16] mm: memcg/slab: replace memcg_from_slab_page() with memcg_from_slab_obj() Roman Gushchin
2019-10-18 0:28 ` [PATCH 13/16] mm: memcg/slab: deprecate memory.kmem.slabinfo Roman Gushchin
2019-10-18 0:28 ` [PATCH 14/16] mm: memcg/slab: use one set of kmem_caches for all memory cgroups Roman Gushchin
2019-10-18 0:28 ` [PATCH 15/16] tools/cgroup: make slabinfo.py compatible with new slab controller Roman Gushchin
2019-10-18 0:28 ` [PATCH 16/16] mm: slab: remove redundant check in memcg_accumulate_slabinfo() Roman Gushchin
2019-10-18 17:03 ` [PATCH 00/16] The new slab memory controller Waiman Long
2019-10-18 17:12 ` Roman Gushchin
2019-10-22 13:22 ` Michal Hocko
2019-10-22 13:28 ` Michal Hocko
2019-10-22 15:48 ` Roman Gushchin
2019-10-22 13:31 ` Michal Hocko
2019-10-22 15:59 ` Roman Gushchin [this message]
-- strict thread matches above, loose matches on Subject: below --
2019-09-05 21:45 [PATCH RFC 00/14] " Roman Gushchin
2019-12-09 9:17 ` [PATCH 00/16] " Bharata B Rao
2019-12-09 11:56 ` Bharata B Rao
2019-12-09 18:04 ` Roman Gushchin
2019-12-10 6:23 ` Bharata B Rao
2019-12-10 18:05 ` Roman Gushchin
2020-01-13 8:47 ` Bharata B Rao
2020-01-13 15:31 ` Roman Gushchin
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