From: Roman Gushchin <guro@fb.com>
To: Johannes Weiner <hannes@cmpxchg.org>
Cc: <linux-mm@kvack.org>, Andrew Morton <akpm@linux-foundation.org>,
Michal Hocko <mhocko@kernel.org>,
Shakeel Butt <shakeelb@google.com>,
Vladimir Davydov <vdavydov.dev@gmail.com>,
<linux-kernel@vger.kernel.org>, <kernel-team@fb.com>,
Bharata B Rao <bharata@linux.ibm.com>,
Yafang Shao <laoar.shao@gmail.com>
Subject: Re: [PATCH v2 12/28] mm: vmstat: use s32 for vm_node_stat_diff in struct per_cpu_nodestat
Date: Mon, 3 Feb 2020 14:28:53 -0800 [thread overview]
Message-ID: <20200203222853.GD6781@xps.dhcp.thefacebook.com> (raw)
In-Reply-To: <20200203203450.GA6380@cmpxchg.org>
On Mon, Feb 03, 2020 at 03:34:50PM -0500, Johannes Weiner wrote:
> On Mon, Feb 03, 2020 at 10:25:06AM -0800, Roman Gushchin wrote:
> > On Mon, Feb 03, 2020 at 12:58:18PM -0500, Johannes Weiner wrote:
> > > On Mon, Jan 27, 2020 at 09:34:37AM -0800, Roman Gushchin wrote:
> > > > Currently s8 type is used for per-cpu caching of per-node statistics.
> > > > It works fine because the overfill threshold can't exceed 125.
> > > >
> > > > But if some counters are in bytes (and the next commit in the series
> > > > will convert slab counters to bytes), it's not gonna work:
> > > > value in bytes can easily exceed s8 without exceeding the threshold
> > > > converted to bytes. So to avoid overfilling per-cpu caches and breaking
> > > > vmstats correctness, let's use s32 instead.
> > > >
> > > > This doesn't affect per-zone statistics. There are no plans to use
> > > > zone-level byte-sized counters, so no reasons to change anything.
> > >
> > > Wait, is this still necessary? AFAIU, the node counters will account
> > > full slab pages, including free space, and only the memcg counters
> > > that track actual objects will be in bytes.
> > >
> > > Can you please elaborate?
> >
> > It's weird to have a counter with the same name (e.g. NR_SLAB_RECLAIMABLE_B)
> > being in different units depending on the accounting scope.
> > So I do convert all slab counters: global, per-lruvec,
> > and per-memcg to bytes.
>
> Since the node counters tracks allocated slab pages and the memcg
> counter tracks allocated objects, arguably they shouldn't use the same
> name anyway.
>
> > Alternatively I can fork them, e.g. introduce per-memcg or per-lruvec
> > NR_SLAB_RECLAIMABLE_OBJ
> > NR_SLAB_UNRECLAIMABLE_OBJ
>
> Can we alias them and reuse their slots?
>
> /* Reuse the node slab page counters item for charged objects */
> MEMCG_SLAB_RECLAIMABLE = NR_SLAB_RECLAIMABLE,
> MEMCG_SLAB_UNRECLAIMABLE = NR_SLAB_UNRECLAIMABLE,
Yeah, lgtm.
Isn't MEMCG_ prefix bad because it makes everybody think that it belongs to
the enum memcg_stat_item?
>
> > and keep global counters untouched. If going this way, I'd prefer to make
> > them per-memcg, because it will simplify things on charging paths:
> > now we do get task->mem_cgroup->obj_cgroup in the pre_alloc_hook(),
> > and then obj_cgroup->mem_cgroup in the post_alloc_hook() just to
> > bump per-lruvec counters.
>
> I don't quite follow. Don't you still have to update the global
> counters?
Global counters are updated only if an allocation requires a new slab
page, which isn't the most common path.
In generic case post_hook is required because it's the only place where
we have both page (to get the node) and memcg pointer.
If NR_SLAB_RECLAIMABLE is tracked only per-memcg (as MEMCG_SOCK),
then post_hook can handle only the rare "allocation failed" case.
I'm not sure here what's better.
>
> > Btw, I wonder if we really need per-lruvec counters at all (at least
> > being enabled by default). For the significant amount of users who
> > have a single-node machine it doesn't bring anything except performance
> > overhead.
>
> Yeah, for single-node systems we should be able to redirect everything
> to the memcg counters, without allocating and tracking lruvec copies.
Sounds good. It can lead to significant savings on single-node machines.
>
> > For those who have multiple nodes (and most likely many many
> > memory cgroups) it provides way too many data except for debugging
> > some weird mm issues.
> > I guess in the absolute majority of cases having global per-node + per-memcg
> > counters will be enough.
>
> Hm? Reclaim uses the lruvec counters.
Can you, please, provide some examples? It looks like it's mostly based
on per-zone lruvec size counters.
Anyway, it seems to be a little bit off from this patchset, so let's
discuss it separately.
next prev parent reply other threads:[~2020-02-03 22:29 UTC|newest]
Thread overview: 84+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-27 17:34 [PATCH v2 00/28] The new cgroup slab memory controller Roman Gushchin
2020-01-27 17:34 ` [PATCH v2 01/28] mm: kmem: cleanup (__)memcg_kmem_charge_memcg() arguments Roman Gushchin
2020-01-27 17:34 ` [PATCH v2 02/28] mm: kmem: cleanup memcg_kmem_uncharge_memcg() arguments Roman Gushchin
2020-01-27 17:34 ` [PATCH v2 03/28] mm: kmem: rename memcg_kmem_(un)charge() into memcg_kmem_(un)charge_page() Roman Gushchin
2020-01-27 17:34 ` [PATCH v2 04/28] mm: kmem: switch to nr_pages in (__)memcg_kmem_charge_memcg() Roman Gushchin
2020-01-27 17:34 ` [PATCH v2 05/28] mm: memcg/slab: cache page number in memcg_(un)charge_slab() Roman Gushchin
2020-01-27 17:34 ` [PATCH v2 06/28] mm: kmem: rename (__)memcg_kmem_(un)charge_memcg() to __memcg_kmem_(un)charge() Roman Gushchin
2020-01-27 17:34 ` [PATCH v2 07/28] mm: memcg/slab: introduce mem_cgroup_from_obj() Roman Gushchin
2020-02-03 16:05 ` Johannes Weiner
2020-01-27 17:34 ` [PATCH v2 08/28] mm: fork: fix kernel_stack memcg stats for various stack implementations Roman Gushchin
2020-02-03 16:12 ` Johannes Weiner
2020-01-27 17:34 ` [PATCH v2 09/28] mm: memcg/slab: rename __mod_lruvec_slab_state() into __mod_lruvec_obj_state() Roman Gushchin
2020-02-03 16:13 ` Johannes Weiner
2020-01-27 17:34 ` [PATCH v2 10/28] mm: memcg: introduce mod_lruvec_memcg_state() Roman Gushchin
2020-02-03 17:39 ` Johannes Weiner
2020-01-27 17:34 ` [PATCH v2 11/28] mm: slub: implement SLUB version of obj_to_index() Roman Gushchin
2020-02-03 17:44 ` Johannes Weiner
2020-01-27 17:34 ` [PATCH v2 12/28] mm: vmstat: use s32 for vm_node_stat_diff in struct per_cpu_nodestat Roman Gushchin
2020-02-03 17:58 ` Johannes Weiner
2020-02-03 18:25 ` Roman Gushchin
2020-02-03 20:34 ` Johannes Weiner
2020-02-03 22:28 ` Roman Gushchin [this message]
2020-02-03 22:39 ` Johannes Weiner
2020-02-04 1:44 ` Roman Gushchin
2020-01-27 17:34 ` [PATCH v2 13/28] mm: vmstat: convert slab vmstat counter to bytes Roman Gushchin
2020-01-27 17:34 ` [PATCH v2 14/28] mm: memcontrol: decouple reference counting from page accounting Roman Gushchin
2020-01-27 17:34 ` [PATCH v2 15/28] mm: memcg/slab: obj_cgroup API Roman Gushchin
2020-02-03 19:31 ` Johannes Weiner
2020-01-27 17:34 ` [PATCH v2 16/28] mm: memcg/slab: allocate obj_cgroups for non-root slab pages Roman Gushchin
2020-02-03 18:27 ` Johannes Weiner
2020-02-03 18:34 ` Roman Gushchin
2020-02-03 20:46 ` Johannes Weiner
2020-02-03 21:19 ` Roman Gushchin
2020-02-03 22:29 ` Johannes Weiner
2020-01-27 17:34 ` [PATCH v2 17/28] mm: memcg/slab: save obj_cgroup for non-root slab objects Roman Gushchin
2020-02-03 19:53 ` Johannes Weiner
2020-01-27 17:34 ` [PATCH v2 18/28] mm: memcg/slab: charge individual slab objects instead of pages Roman Gushchin
2020-01-27 17:34 ` [PATCH v2 19/28] mm: memcg/slab: deprecate memory.kmem.slabinfo Roman Gushchin
2020-01-27 17:34 ` [PATCH v2 20/28] mm: memcg/slab: move memcg_kmem_bypass() to memcontrol.h Roman Gushchin
2020-01-27 17:34 ` [PATCH v2 21/28] mm: memcg/slab: use a single set of kmem_caches for all memory cgroups Roman Gushchin
2020-02-03 19:50 ` Johannes Weiner
2020-02-03 20:58 ` Roman Gushchin
2020-02-03 22:17 ` Johannes Weiner
2020-02-03 22:38 ` Roman Gushchin
2020-02-04 1:15 ` Roman Gushchin
2020-02-04 2:47 ` Johannes Weiner
2020-02-04 4:35 ` Roman Gushchin
2020-02-04 18:41 ` Johannes Weiner
2020-02-05 15:58 ` Roman Gushchin
2020-01-27 17:34 ` [PATCH v2 22/28] mm: memcg/slab: simplify memcg cache creation Roman Gushchin
2020-01-27 17:34 ` [PATCH v2 23/28] mm: memcg/slab: deprecate memcg_kmem_get_cache() Roman Gushchin
2020-01-27 17:34 ` [PATCH v2 24/28] mm: memcg/slab: deprecate slab_root_caches Roman Gushchin
2020-01-27 17:34 ` [PATCH v2 25/28] mm: memcg/slab: remove redundant check in memcg_accumulate_slabinfo() Roman Gushchin
2020-01-27 17:34 ` [PATCH v2 26/28] tools/cgroup: add slabinfo.py tool Roman Gushchin
2020-01-27 17:34 ` [PATCH v2 27/28] tools/cgroup: make slabinfo.py compatible with new slab controller Roman Gushchin
2020-01-30 2:17 ` Bharata B Rao
2020-01-30 2:44 ` Roman Gushchin
2020-01-31 22:24 ` Roman Gushchin
2020-02-12 5:21 ` Bharata B Rao
2020-02-12 20:42 ` Roman Gushchin
2020-01-27 17:34 ` [PATCH v2 28/28] kselftests: cgroup: add kernel memory accounting tests Roman Gushchin
2020-01-30 2:06 ` [PATCH v2 00/28] The new cgroup slab memory controller Bharata B Rao
2020-01-30 2:41 ` Roman Gushchin
2020-08-12 23:16 ` Pavel Tatashin
2020-08-12 23:18 ` Pavel Tatashin
2020-08-13 0:04 ` Roman Gushchin
2020-08-13 0:31 ` Pavel Tatashin
2020-08-28 16:47 ` Pavel Tatashin
2020-09-01 5:28 ` Bharata B Rao
2020-09-01 12:52 ` Pavel Tatashin
2020-09-02 6:23 ` Bharata B Rao
2020-09-02 12:34 ` Pavel Tatashin
2020-09-02 9:53 ` Vlastimil Babka
2020-09-02 10:39 ` David Hildenbrand
2020-09-02 12:42 ` Pavel Tatashin
2020-09-02 13:50 ` Michal Hocko
2020-09-02 14:20 ` Pavel Tatashin
2020-09-03 18:09 ` David Hildenbrand
2020-09-02 11:26 ` Michal Hocko
2020-09-02 12:51 ` Pavel Tatashin
2020-09-02 13:51 ` Michal Hocko
2020-09-02 11:32 ` Michal Hocko
2020-09-02 12:53 ` Pavel Tatashin
2020-09-02 13:52 ` Michal Hocko
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