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

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Message-Id: <20141102.232245.1502900027200657150.davem@davemloft.net>
Date:	Sun, 02 Nov 2014 23:22:45 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	hannes@...xchg.org
Cc:	akpm@...ux-foundation.org, mhocko@...e.cz, vdavydov@...allels.com,
	tj@...nel.org, 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

From: Johannes Weiner <hannes@...xchg.org>
Date: Sat,  1 Nov 2014 23:15:54 -0400

> 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>

Looks great:

Acked-by: David S. Miller <davem@...emloft.net>
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