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 15:48:17 +0000 [thread overview]
Message-ID: <20191022154812.GA21381@tower.DHCP.thefacebook.com> (raw)
In-Reply-To: <20191022132800.GO9379@dhcp22.suse.cz>
On Tue, Oct 22, 2019 at 03:28:00PM +0200, Michal Hocko wrote:
> On Tue 22-10-19 15:22:06, Michal Hocko wrote:
> > On Thu 17-10-19 17:28:04, Roman Gushchin wrote:
> > [...]
> > > Using a drgn* script I've got an estimation of slab utilization on
> > > a number of machines running different production workloads. In most
> > > cases it was between 45% and 65%, and the best number I've seen was
> > > around 85%. Turning kmem accounting off brings it to high 90s. Also
> > > it brings back 30-50% of slab memory. It means that the real price
> > > of the existing slab memory controller is way bigger than a pointer
> > > per page.
> >
> > How much of the memory are we talking about here?
>
> Just to be more specific. Your cover mentions several hundreds of MBs
> but there is no scale to the overal charged memory. How much of that is
> the actual kmem accounted memory.
As I wrote, on average it saves 30-45% of slab memory.
The smallest number I've seen was about 15%, the largest over 60%.
The amount of slab memory isn't a very stable metrics in general: it heavily
depends on workload pattern, memory pressure, uptime etc.
In absolute numbers I've seen savings from ~60 Mb for an empty vm to
more than 2 Gb for some production workloads.
Btw, please note that after a recent change from Vlastimil
6a486c0ad4dc ("mm, sl[ou]b: improve memory accounting")
slab counters are including large allocations which are passed
directly to the page allocator. It will makes memory savings
smaller in percents, but of course not in absolute numbers.
>
> > Also is there any pattern for specific caches that tend to utilize
> > much worse than others?
Caches which usually have many objects (e.g. inodes) initially
have a better utilization, but as some of them are getting reclaimed
the utilization drops. And if the cgroup is already dead, no one can
reuse these mostly slab empty pages, so it's pretty wasteful.
So I don't think the problem is specific to any cache, it's pretty general.
next prev parent reply other threads:[~2019-10-22 15:48 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 [this message]
2019-10-22 13:31 ` Michal Hocko
2019-10-22 15:59 ` Roman Gushchin
-- 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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