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From: Jesper Dangaard Brouer <brouer@redhat.com>
To: Roman Gushchin <guro@fb.com>
Cc: Vlastimil Babka <vbabka@suse.cz>,
	Shakeel Butt <shakeelb@google.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Christoph Lameter <cl@linux.com>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Michal Hocko <mhocko@kernel.org>, Linux MM <linux-mm@kvack.org>,
	Kernel Team <kernel-team@fb.com>,
	LKML <linux-kernel@vger.kernel.org>,
	Mel Gorman <mgorman@techsingularity.net>,
	brouer@redhat.com
Subject: Re: [PATCH v6 00/19] The new cgroup slab memory controller
Date: Fri, 19 Jun 2020 10:32:47 +0200
Message-ID: <20200619103247.7b8bc9ad@carbon> (raw)
In-Reply-To: <20200619013013.GE135965@carbon.dhcp.thefacebook.com>

On Thu, 18 Jun 2020 18:30:13 -0700
Roman Gushchin <guro@fb.com> wrote:

> On Thu, Jun 18, 2020 at 11:31:21AM +0200, Jesper Dangaard Brouer wrote:
> > On Thu, 18 Jun 2020 10:43:44 +0200
> > Jesper Dangaard Brouer <brouer@redhat.com> wrote:
> >   
> > > On Wed, 17 Jun 2020 18:29:28 -0700
> > > Roman Gushchin <guro@fb.com> wrote:
> > >   
> > > > On Wed, Jun 17, 2020 at 01:24:21PM +0200, Vlastimil Babka wrote:    
> > > > > On 6/17/20 5:32 AM, Roman Gushchin wrote:      
> > > > > > On Tue, Jun 16, 2020 at 08:05:39PM -0700, Shakeel Butt wrote:      
> > > > > >> On Tue, Jun 16, 2020 at 7:41 PM Roman Gushchin <guro@fb.com> wrote:      
> > > > > >> >
> > > > > >> > On Tue, Jun 16, 2020 at 06:46:56PM -0700, Shakeel Butt wrote:      
> > > > > >> > > On Mon, Jun 8, 2020 at 4:07 PM Roman Gushchin <guro@fb.com> wrote:      
> > > > > >> > > >      
> > > > > >> [...]      
> > > > > >> > >
> > > > > >> > > Have you performed any [perf] testing on SLAB with this patchset?      
> > > > > >> >
> > > > > >> > The accounting part is the same for SLAB and SLUB, so there should be no
> > > > > >> > significant difference. I've checked that it compiles, boots and passes
> > > > > >> > kselftests. And that memory savings are there.
> > > > > >> >      
> > > > > >> 
> > > > > >> What about performance? Also you mentioned that sharing kmem-cache
> > > > > >> between accounted and non-accounted can have additional overhead. Any
> > > > > >> difference between SLAB and SLUB for such a case?      
> > > > > > 
> > > > > > Not really.
> > > > > > 
> > > > > > Sharing a single set of caches adds some overhead to root- and non-accounted
> > > > > > allocations, which is something I've tried hard to avoid in my original version.
> > > > > > But I have to admit, it allows to simplify and remove a lot of code, and here
> > > > > > it's hard to argue with Johanness, who pushed on this design.
> > > > > > 
> > > > > > With performance testing it's not that easy, because it's not obvious what
> > > > > > we wanna test. Obviously, per-object accounting is more expensive, and
> > > > > > measuring something like 1000000 allocations and deallocations in a line from
> > > > > > a single kmem_cache will show a regression. But in the real world the relative
> > > > > > cost of allocations is usually low, and we can get some benefits from a smaller
> > > > > > working set and from having shared kmem_cache objects cache hot.
> > > > > > Not speaking about some extra memory and the fragmentation reduction.
> > > > > > 
> > > > > > We've done an extensive testing of the original version in Facebook production,
> > > > > > and we haven't noticed any regressions so far. But I have to admit, we were
> > > > > > using an original version with two sets of kmem_caches.
> > > > > > 
> > > > > > If you have any specific tests in mind, I can definitely run them. Or if you
> > > > > > can help with the performance evaluation, I'll appreciate it a lot.      
> > > > > 
> > > > > Jesper provided some pointers here [1], it would be really great if you could
> > > > > run at least those microbenchmarks. With mmtests it's the major question of
> > > > > which subset/profiles to run, maybe the referenced commits provide some hints,
> > > > > or maybe Mel could suggest what he used to evaluate SLAB vs SLUB not so long ago.
> > > > > 
> > > > > [1] https://lore.kernel.org/linux-mm/20200527103545.4348ac10@carbon/      
> > > > 
> > > > Oh, Jesper, I'm really sorry, somehow I missed your mail.
> > > > Thank you, Vlastimil, for pointing at it.
> > > > 
> > > > I've got some results (slab_bulk_test01), but honestly I fail to interpret them.
> > > > 
> > > > I ran original vs patched with SLUB and SLAB, each test several times and picked
> > > > 3 which looked most consistently. But it still looks very noisy.
> > > > 
> > > > I ran them on my desktop (8-core Ryzen 1700, 16 GB RAM, Fedora 32),
> > > > it's 5.8-rc1 + slab controller v6 vs 5.8-rc1 (default config from Fedora 32).    
> > > 
> > > What about running these tests on the server level hardware, that you
> > > intent to run this on?    
> > 
> > To give you an idea of the performance difference I ran the same test
> > on a Broadwell Intel(R) Xeon(R) CPU E5-1650 v4 @ 3.60GHz.
> > 
> > The SLUB fastpath:
> >  Type:kmem fastpath reuse Per elem: 60 cycles(tsc) 16.822 ns
> > 
> >   
> > > > 
> > > > How should I interpret this data?    
> > > 
> > > First of all these SLUB+SLAB microbenchmarks use object size 256 bytes,
> > > because network stack alloc object of this size for SKBs/sk_buff (due
> > > to cache-align as used size is 224 bytes). Checked SLUB: Each slab use
> > > 2 pages (8192 bytes) and contain 32 object of size 256 (256*32=8192).
> > > 
> > >   The SLUB allocator have a per-CPU slab which speedup fast-reuse, in this
> > > case up-to 32 objects. For SLUB the "fastpath reuse" test this behaviour,
> > > and it serves as a baseline for optimal 1-object performance (where my bulk
> > > API tries to beat that, which is possible even for 1-object due to knowing
> > > bulk API cannot be used from IRQ context).
> > > 
> > > SLUB fastpath: 3 measurements reporting cycles(tsc)
> > >  - SLUB-patched : fastpath reuse: 184 - 177 - 176  cycles(tsc)
> > >  - SLUB-original: fastpath reuse: 178 - 153 - 156  cycles(tsc)
> > >   
> > 
> > For your SLAB results:
> > 
> >  SLAB fastpath: 3 measurements reporting cycles(tsc)
> >   - SLAB-patched : 161 - 160 - 163  cycles(tsc)
> >   - SLAB-original: 174 - 170 - 159  cycles(tsc)
> > 
> > I find it strange that SLAB is slightly better than SLUB (in many
> > measurements), because SLUB should have an advantage on this fast-path
> > quick reuse due to the per-CPU slabs.  Maybe this is also related to
> > the CPU arch you are using?
> > 
> >   
> > > There are some stability concerns as you mention, but it seems pretty
> > > consistently that patched version is slower. If you compile with
> > > no-PREEMPT you can likely get more stable results (and remove a slight
> > > overhead for SLUB fastpath).
> > > 
> > > The microbenchmark also measures the bulk-API, which is AFAIK only used
> > > by network stack (and io_uring). I guess you shouldn't focus too much
> > > on these bulk measurements. When bulk-API cross this objects per slab
> > > threshold, or is unlucky is it use two per-CPU slab, then the
> > > measurements can fluctuate a bit.
> > > 
> > > Your numbers for SLUB bulk-API:
> > > 
> > > SLUB-patched - bulk-API
> > >  - SLUB-patched : bulk_quick_reuse objects=1 : 187 -  90 - 224  cycles(tsc)
> > >  - SLUB-patched : bulk_quick_reuse objects=2 : 110 -  53 - 133  cycles(tsc)
> > >  - SLUB-patched : bulk_quick_reuse objects=3 :  88 -  95 -  42  cycles(tsc)
> > >  - SLUB-patched : bulk_quick_reuse objects=4 :  91 -  85 -  36  cycles(tsc)
> > >  - SLUB-patched : bulk_quick_reuse objects=8 :  32 -  66 -  32  cycles(tsc)
> > > 
> > > SLUB-original -  bulk-API
> > >  - SLUB-original: bulk_quick_reuse objects=1 :  87 -  87 - 142  cycles(tsc)
> > >  - SLUB-original: bulk_quick_reuse objects=2 :  52 -  53 -  53  cycles(tsc)
> > >  - SLUB-original: bulk_quick_reuse objects=3 :  42 -  42 -  91  cycles(tsc)
> > >  - SLUB-original: bulk_quick_reuse objects=4 :  91 -  37 -  37  cycles(tsc)
> > >  - SLUB-original: bulk_quick_reuse objects=8 :  31 -  79 -  76  cycles(tsc)  
> > 
> > Your numbers for SLAB bulk-API:
> > 
> > SLAB-patched -  bulk-API
> >  - SLAB-patched : bulk_quick_reuse objects=1 :  67 -  67 - 140  cycles(tsc)
> >  - SLAB-patched : bulk_quick_reuse objects=2 :  55 -  46 -  46  cycles(tsc)
> >  - SLAB-patched : bulk_quick_reuse objects=3 :  93 -  94 -  39  cycles(tsc)
> >  - SLAB-patched : bulk_quick_reuse objects=4 :  35 -  88 -  85  cycles(tsc)
> >  - SLAB-patched : bulk_quick_reuse objects=8 :  30 -  30 -  30  cycles(tsc)
> > 
> > SLAB-original-  bulk-API
> >  - SLAB-original: bulk_quick_reuse objects=1 : 143 - 136 -  67  cycles(tsc)
> >  - SLAB-original: bulk_quick_reuse objects=2 :  45 -  46 -  46  cycles(tsc)
> >  - SLAB-original: bulk_quick_reuse objects=3 :  38 -  39 -  39  cycles(tsc)
> >  - SLAB-original: bulk_quick_reuse objects=4 :  35 -  87 -  87  cycles(tsc)
> >  - SLAB-original: bulk_quick_reuse objects=8 :  29 -  66 -  30  cycles(tsc)
> > 
> > In case of SLAB I expect the bulk-API to be slightly faster than SLUB,
> > as the SLUB bulk code is much more advanced.  
> 
> So again it looks like a patched version is only slightly worse if we're taking
> the smallest number in each series. Is it a correct assumption?

Yes, I guess that is a good way to look at these somewhat fluctuating numbers.

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer


  reply index

Thread overview: 92+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-08 23:06 Roman Gushchin
2020-06-08 23:06 ` [PATCH v6 01/19] mm: memcg: factor out memcg- and lruvec-level changes out of __mod_lruvec_state() Roman Gushchin
2020-06-17  1:52   ` Shakeel Butt
2020-06-17  2:50     ` Roman Gushchin
2020-06-17  2:59       ` Shakeel Butt
2020-06-17  3:19         ` Roman Gushchin
2020-06-08 23:06 ` [PATCH v6 02/19] mm: memcg: prepare for byte-sized vmstat items Roman Gushchin
2020-06-17  2:57   ` Shakeel Butt
2020-06-17  3:19     ` Roman Gushchin
2020-06-17 15:55   ` Shakeel Butt
2020-06-08 23:06 ` [PATCH v6 03/19] mm: memcg: convert vmstat slab counters to bytes Roman Gushchin
2020-06-17  3:03   ` Shakeel Butt
2020-06-08 23:06 ` [PATCH v6 04/19] mm: slub: implement SLUB version of obj_to_index() Roman Gushchin
2020-06-17  3:08   ` Shakeel Butt
2020-06-08 23:06 ` [PATCH v6 05/19] mm: memcontrol: decouple reference counting from page accounting Roman Gushchin
2020-06-18  0:47   ` Shakeel Butt
2020-06-18 14:55   ` Shakeel Butt
2020-06-18 19:51     ` Roman Gushchin
2020-06-19  1:08     ` Roman Gushchin
2020-06-19  1:18       ` Shakeel Butt
2020-06-19  1:31   ` Shakeel Butt
2020-06-08 23:06 ` [PATCH v6 06/19] mm: memcg/slab: obj_cgroup API Roman Gushchin
2020-06-19 15:42   ` Shakeel Butt
2020-06-19 21:38     ` Roman Gushchin
2020-06-19 22:16       ` Shakeel Butt
2020-06-19 22:52         ` Roman Gushchin
2020-06-20 22:50       ` Andrew Morton
2020-06-08 23:06 ` [PATCH v6 07/19] mm: memcg/slab: allocate obj_cgroups for non-root slab pages Roman Gushchin
2020-06-19 16:36   ` Shakeel Butt
2020-06-20  0:25     ` Roman Gushchin
2020-06-20  0:31       ` Shakeel Butt
2020-06-08 23:06 ` [PATCH v6 08/19] mm: memcg/slab: save obj_cgroup for non-root slab objects Roman Gushchin
2020-06-20  0:16   ` Shakeel Butt
2020-06-20  1:19     ` Roman Gushchin
2020-06-08 23:06 ` [PATCH v6 09/19] mm: memcg/slab: charge individual slab objects instead of pages Roman Gushchin
2020-06-20  0:54   ` Shakeel Butt
2020-06-20  1:29     ` Roman Gushchin
2020-06-08 23:06 ` [PATCH v6 10/19] mm: memcg/slab: deprecate memory.kmem.slabinfo Roman Gushchin
2020-06-22 17:12   ` Shakeel Butt
2020-06-22 18:01     ` Roman Gushchin
2020-06-22 18:09       ` Shakeel Butt
2020-06-22 18:25         ` Roman Gushchin
2020-06-22 18:38           ` Shakeel Butt
2020-06-08 23:06 ` [PATCH v6 11/19] mm: memcg/slab: move memcg_kmem_bypass() to memcontrol.h Roman Gushchin
2020-06-20  1:19   ` Shakeel Butt
2020-06-08 23:06 ` [PATCH v6 12/19] mm: memcg/slab: use a single set of kmem_caches for all accounted allocations Roman Gushchin
2020-06-22 16:56   ` Shakeel Butt
2020-06-08 23:06 ` [PATCH v6 13/19] mm: memcg/slab: simplify memcg cache creation Roman Gushchin
2020-06-22 17:29   ` Shakeel Butt
2020-06-22 17:40     ` Roman Gushchin
2020-06-22 18:03       ` Shakeel Butt
2020-06-08 23:06 ` [PATCH v6 14/19] mm: memcg/slab: remove memcg_kmem_get_cache() Roman Gushchin
2020-06-22 18:42   ` Shakeel Butt
2020-06-08 23:06 ` [PATCH v6 15/19] mm: memcg/slab: deprecate slab_root_caches Roman Gushchin
2020-06-22 17:36   ` Shakeel Butt
2020-06-08 23:06 ` [PATCH v6 16/19] mm: memcg/slab: remove redundant check in memcg_accumulate_slabinfo() Roman Gushchin
2020-06-22 17:32   ` Shakeel Butt
2020-06-08 23:06 ` [PATCH v6 17/19] mm: memcg/slab: use a single set of kmem_caches for all allocations Roman Gushchin
2020-06-17 23:35   ` Andrew Morton
2020-06-18  0:35     ` Roman Gushchin
2020-06-18  7:33       ` Vlastimil Babka
2020-06-18 19:54         ` Roman Gushchin
2020-06-22 19:21   ` Shakeel Butt
2020-06-22 20:37     ` Roman Gushchin
2020-06-22 21:04       ` Shakeel Butt
2020-06-22 21:13         ` Roman Gushchin
2020-06-22 21:28           ` Shakeel Butt
2020-06-22 21:58             ` Roman Gushchin
2020-06-22 22:05               ` Shakeel Butt
2020-06-08 23:06 ` [PATCH v6 18/19] kselftests: cgroup: add kernel memory accounting tests Roman Gushchin
2020-06-17  1:46 ` [PATCH v6 00/19] The new cgroup slab memory controller Shakeel Butt
2020-06-17  2:41   ` Roman Gushchin
2020-06-17  3:05     ` Shakeel Butt
2020-06-17  3:32       ` Roman Gushchin
2020-06-17 11:24         ` Vlastimil Babka
2020-06-17 14:31           ` Mel Gorman
2020-06-20  0:57             ` Roman Gushchin
2020-06-18  1:29           ` Roman Gushchin
2020-06-18  8:43             ` Jesper Dangaard Brouer
2020-06-18  9:31               ` Jesper Dangaard Brouer
2020-06-19  1:30                 ` Roman Gushchin
2020-06-19  8:32                   ` Jesper Dangaard Brouer [this message]
2020-06-19  1:27               ` Roman Gushchin
2020-06-19  9:39                 ` Jesper Dangaard Brouer
2020-06-19 18:47                   ` Roman Gushchin
2020-06-18  1:18   ` Roman Gushchin
2020-06-18  9:27 ` Mike Rapoport
2020-06-18 20:43   ` Roman Gushchin
2020-06-21 22:57 ` Qian Cai
2020-06-21 23:34   ` Roman Gushchin
2020-06-21 23:53     ` Qian Cai
2020-06-22  3:07       ` Roman Gushchin

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