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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20150519161422.GA10561@cmpxchg.org>
Date:	Tue, 19 May 2015 12:14:22 -0400
From:	Johannes Weiner <hannes@...xchg.org>
To:	Vlastimil Babka <vbabka@...e.cz>
Cc:	Mel Gorman <mgorman@...e.de>, Michal Hocko <mhocko@...e.cz>,
	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, May 19, 2015 at 05:25:36PM +0200, Vlastimil Babka wrote:
> On 05/19/2015 05:13 PM, Mel Gorman wrote:
> >### MEL: Function entry, check for mem_cgroup_disabled()
> >
> >
> >                :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
> >
> >#### MEL: I was surprised to see this atrocity. It's a PageSwapCache check
> 
> Looks like sampling is off by instruction, because why would a reg->reg mov
> took so long. So it's probably a cache miss on struct page, pointer to which
> is in rdi. Which is weird, I would expect memcg to be called on struct pages
> that are already hot.

Yeah, anonymous faults do __SetPageUptodate() right before passing the
page into mem_cgroup_try_charge().  page->flags should be hot.

> It would also mean that if you don't fetch the struct
> page from the memcg code, then the following code in the caller will most
> likely work on the struct page and get the cache miss anyway?

Which is why the runtime reduction doesn't match the profile
reduction.  The cost seems to get shifted somewhere else.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/