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From: Roman Gushchin <guro@fb.com>
To: Christopher Lameter <cl@linux.com>
Cc: "linux-mm@kvack.org" <linux-mm@kvack.org>,
	Michal Hocko <mhocko@kernel.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>
Subject: Re: [PATCH 02/16] mm: vmstat: use s32 for vm_node_stat_diff in struct per_cpu_nodestat
Date: Mon, 21 Oct 2019 01:21:02 +0000	[thread overview]
Message-ID: <20191021012056.GB8869@castle> (raw)
In-Reply-To: <alpine.DEB.2.21.1910202250010.593@www.lameter.com>

On Sun, Oct 20, 2019 at 10:51:10PM +0000, Christopher Lameter wrote:
> On Thu, 17 Oct 2019, 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.
> 
> Actually this is inconsistenct since the other counters are all used to
> account for pages. Some of the functions in use for the page counters will
> no longer make sense. inc/dec_node_state() etc.

Actually I tried to implement what Johannes suggested earlier and convert
all counters to bytes, but it looked like it can lead to a significant
performance hit on 32bit platforms, as I'd need to replace all atomic_long_t
with atomic64_t. Also, to make the code look good, I'd need to convert
all counters to bytes (and atomic64_t): zone stats, vmevents, etc.
So I gave up relatively quickly.

Maybe it's a good long-term plan, but as now it doesn't really look
as an obviously good think to do.

I'm fully open to any suggestions here.

  reply	other threads:[~2019-10-21  1:21 UTC|newest]

Thread overview: 36+ 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 [this message]
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

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