linux-kernel - Re: [PATCH] mm, memcg: Optionally disable memcg by default using Kconfig

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Message-ID: <20150519152710.GK6203@dhcp22.suse.cz>
Date:	Tue, 19 May 2015 17:27:10 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Mel Gorman <mgorman@...e.de>
Cc:	Johannes Weiner <hannes@...xchg.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Tejun Heo <tj@...nel.org>, cgroups@...r.kernel.org
Subject: Re: [PATCH] mm, memcg: Optionally disable memcg by default using
 Kconfig

On Tue 19-05-15 16:13:02, Mel Gorman wrote:
[...]
>                :ffffffff811c160f:       je     ffffffff811c1630 <mem_cgroup_try_charge+0x40>
>                :ffffffff811c1611:       xor    %eax,%eax
>                :ffffffff811c1613:       xor    %ebx,%ebx
>      1 1.7e-05 :ffffffff811c1615:       mov    %rbx,(%r12)
>      7 1.2e-04 :ffffffff811c1619:       add    $0x10,%rsp
>   1211  0.0203 :ffffffff811c161d:       pop    %rbx
>      5 8.4e-05 :ffffffff811c161e:       pop    %r12
>      5 8.4e-05 :ffffffff811c1620:       pop    %r13
>   1249  0.0210 :ffffffff811c1622:       pop    %r14
>      7 1.2e-04 :ffffffff811c1624:       pop    %rbp
>      5 8.4e-05 :ffffffff811c1625:       retq   
>                :ffffffff811c1626:       nopw   %cs:0x0(%rax,%rax,1)
>    295  0.0050 :ffffffff811c1630:       mov    (%rdi),%rax
> 160703  2.6973 :ffffffff811c1633:       mov    %edx,%r13d

Huh, what? Even if this was off by one and the preceding instruction has
consumed the time. This would be reading from page->flags but the page
should be hot by the time we got here, no?

> #### MEL: I was surprised to see this atrocity. It's a PageSwapCache check
> #### /usr/src/linux-4.0-vanilla/./arch/x86/include/asm/bitops.h:311
> #### /usr/src/linux-4.0-vanilla/include/linux/page-flags.h:261
> #### /usr/src/linux-4.0-vanilla/mm/memcontrol.c:5473
-- 
Michal Hocko
SUSE Labs
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