From: David Miller <davem@davemloft.net>
To: kirill@shutemov.name
Cc: hannes@cmpxchg.org, akpm@linux-foundation.org, mhocko@suse.cz,
vdavydov@parallels.com, tj@kernel.org, linux-mm@kvack.org,
cgroups@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [patch 1/3] mm: embed the memcg pointer directly into struct page
Date: Mon, 03 Nov 2014 16:58:07 -0500 (EST) [thread overview]
Message-ID: <20141103.165807.2039166055692354811.davem@davemloft.net> (raw)
In-Reply-To: <20141103215206.GB24091@node.dhcp.inet.fi>
From: "Kirill A. Shutemov" <kirill@shutemov.name>
Date: Mon, 3 Nov 2014 23:52:06 +0200
> On Mon, Nov 03, 2014 at 04:36:28PM -0500, Johannes Weiner wrote:
>> On Mon, Nov 03, 2014 at 11:06:07PM +0200, Kirill A. Shutemov wrote:
>> > On Sat, Nov 01, 2014 at 11:15:54PM -0400, Johannes Weiner wrote:
>> > > Memory cgroups used to have 5 per-page pointers. To allow users to
>> > > disable that amount of overhead during runtime, those pointers were
>> > > allocated in a separate array, with a translation layer between them
>> > > and struct page.
>> > >
>> > > There is now only one page pointer remaining: the memcg pointer, that
>> > > indicates which cgroup the page is associated with when charged. The
>> > > complexity of runtime allocation and the runtime translation overhead
>> > > is no longer justified to save that *potential* 0.19% of memory.
>> >
>> > How much do you win by the change?
>>
>> Heh, that would have followed right after where you cut the quote:
>> with CONFIG_SLUB, that pointer actually sits in already existing
>> struct page padding, which means that I'm saving one pointer per page
>> (8 bytes per 4096 byte page, 0.19% of memory), plus the pointer and
>> padding in each memory section. I also save the (minor) translation
>> overhead going from page to page_cgroup and the maintenance burden
>> that stems from having these auxiliary arrays (see deleted code).
>
> I read the description. I want to know if runtime win (any benchmark data?)
> from moving mem_cgroup back to the struct page is measurable.
>
> If the win is not significant, I would prefer to not occupy the padding:
> I'm sure we will be able to find a better use for the space in struct page
> in the future.
I think the simplification benefits completely trump any performan
metric.
next prev parent reply other threads:[~2014-11-03 21:58 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-11-02 3:15 [patch 1/3] mm: embed the memcg pointer directly into struct page Johannes Weiner
2014-11-02 3:15 ` [patch 2/3] mm: page_cgroup: rename file to mm/swap_cgroup.c Johannes Weiner
2014-11-03 4:22 ` David Miller
2014-11-03 16:57 ` Michal Hocko
2014-11-03 17:30 ` Vladimir Davydov
2014-11-04 8:37 ` Kamezawa Hiroyuki
2014-11-02 3:15 ` [patch 3/3] mm: move page->mem_cgroup bad page handling into generic code Johannes Weiner
2014-11-03 4:23 ` David Miller
2014-11-03 16:58 ` Michal Hocko
2014-11-03 17:32 ` Vladimir Davydov
2014-11-03 18:27 ` [patch] mm: move page->mem_cgroup bad page handling into generic code fix Johannes Weiner
2014-11-03 20:10 ` David Miller
2014-11-04 8:39 ` [patch 3/3] mm: move page->mem_cgroup bad page handling into generic code Kamezawa Hiroyuki
2014-11-03 4:22 ` [patch 1/3] mm: embed the memcg pointer directly into struct page David Miller
2014-11-03 8:02 ` Joonsoo Kim
2014-11-03 15:09 ` Johannes Weiner
2014-11-03 16:42 ` David Miller
2014-11-03 17:02 ` Michal Hocko
2014-11-04 0:40 ` Joonsoo Kim
2014-11-03 16:51 ` Michal Hocko
2014-11-03 17:17 ` Michal Hocko
2014-11-03 17:30 ` Vladimir Davydov
2014-11-03 21:06 ` Kirill A. Shutemov
2014-11-03 21:36 ` Johannes Weiner
2014-11-03 21:52 ` Kirill A. Shutemov
2014-11-03 21:58 ` David Miller [this message]
2014-11-03 22:36 ` Johannes Weiner
2014-11-04 13:06 ` Michal Hocko
2014-11-04 13:48 ` Johannes Weiner
2014-11-04 14:50 ` Michal Hocko
2014-11-04 8:36 ` Kamezawa Hiroyuki
2014-11-04 13:27 ` Johannes Weiner
2014-11-04 13:41 ` Michal Hocko
2014-11-04 14:09 ` Johannes Weiner
2014-11-04 15:00 ` Michal Hocko
2014-11-04 17:46 ` Johannes Weiner
2014-11-04 16:34 ` David Miller
2014-11-06 18:55 ` Konstantin Khlebnikov
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