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From: Roman Gushchin <guro@fb.com>
To: Muchun Song <songmuchun@bytedance.com>
Cc: <hannes@cmpxchg.org>, <mhocko@kernel.org>,
	<vdavydov.dev@gmail.com>, <akpm@linux-foundation.org>,
	<shakeelb@google.com>, <sfr@canb.auug.org.au>,
	<chris@chrisdown.name>, <laoar.shao@gmail.com>,
	<richard.weiyang@gmail.com>, <linux-kernel@vger.kernel.org>,
	<cgroups@vger.kernel.org>, <linux-mm@kvack.org>
Subject: Re: [PATCH v2] mm: memcontrol: optimize per-lruvec stats counter memory usage
Date: Tue, 8 Dec 2020 18:21:18 -0800	[thread overview]
Message-ID: <20201209022118.GB2385286@carbon.DHCP.thefacebook.com> (raw)
In-Reply-To: <20201208095132.79383-1-songmuchun@bytedance.com>

On Tue, Dec 08, 2020 at 05:51:32PM +0800, Muchun Song wrote:
> The vmstat threshold is 32 (MEMCG_CHARGE_BATCH), so the type of s32
> of lruvec_stat_cpu is enough. And introduce struct per_cpu_lruvec_stat
> to optimize memory usage.
> 
> The size of struct lruvec_stat is 304 bytes on 64 bits system. As it
> is a per-cpu structure. So with this patch, we can save 304 / 2 * ncpu
> bytes per-memcg per-node where ncpu is the number of the possible CPU.
> If there are c memory cgroup (include dying cgroup) and n NUMA node in
> the system. Finally, we can save (152 * ncpu * c * n) bytes.

Honestly, I'm not convinced.
Say, ncpu = 32, n = 2, c = 500. We're saving <5Mb of memory.
If the machine has 128Gb of RAM, it's .000000003%.

Using longs (s64) allows not to think too much about overflows
and can also be slightly faster on 64-bit machines.

Thanks!


  parent reply	other threads:[~2020-12-09  2:21 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-08  9:51 [PATCH v2] mm: memcontrol: optimize per-lruvec stats counter memory usage Muchun Song
2020-12-08 18:20 ` Shakeel Butt
2020-12-09  2:21 ` Roman Gushchin [this message]
2020-12-09  2:28   ` Roman Gushchin
2020-12-09  2:31   ` [External] " Muchun Song
2020-12-09  3:52     ` Roman Gushchin
2020-12-09  7:05       ` Muchun Song

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