linux-kernel - Re: [patch 1/3] mm: embed the memcg pointer directly into struct page

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Message-ID: <20141103173024.GU17258@esperanza>
Date:	Mon, 3 Nov 2014 20:30:24 +0300
From:	Vladimir Davydov <vdavydov@...allels.com>
To:	Johannes Weiner <hannes@...xchg.org>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Michal Hocko <mhocko@...e.cz>, Tejun Heo <tj@...nel.org>,
	David Miller <davem@...emloft.net>, <linux-mm@...ck.org>,
	<cgroups@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [patch 1/3] mm: embed the memcg pointer directly into struct page

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.  With
> CONFIG_SLUB, page->mem_cgroup actually sits in the doubleword padding
> after the page->private member and doesn't even increase struct page,
> and then this patch actually saves space.  Remaining users that care
> can still compile their kernels without CONFIG_MEMCG.
> 
>    text    data     bss     dec     hex     filename
> 8828345 1725264  983040 11536649 b00909  vmlinux.old
> 8827425 1725264  966656 11519345 afc571  vmlinux.new
> 
> Signed-off-by: Johannes Weiner <hannes@...xchg.org>

Acked-by: Vladimir Davydov <vdavydov@...allels.com>
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