Re: [question] call mark_page_accessed() in minor fault

[Zheng Liu <gnehzuil.liu@gmail.com>]

On Sat, Apr 27, 2013 at 03:10:30PM +0800, Simon Jeons wrote:
> Hi Zheng,
> On 04/23/2013 09:49 PM, Zheng Liu wrote:
> >Hi Konstantin,
> >
> >On Tue, Apr 23, 2013 at 05:02:34PM +0400, Konstantin Khlebnikov wrote:
> >>Zheng Liu wrote:
> >>>Hi all,
> >>>
> >>>Recently we meet a performance regression about mmaped page.  When we upgrade
> >>>our product system from 2.6.18 kernel to a latest kernel, such as 2.6.32 kernel,
> >>>we will find that mmaped pages are reclaimed very quickly.  We found that when
> >>>we hit a minor fault mark_page_accessed() is called in 2.6.18 kernel, but in
> >>>2.6.32 kernel we don't call mark_page_accesed().  This means that mmaped pages
> >>>in 2.6.18 kernel are activated and moved into active list.  While in 2.6.32
> >>>kernel mmaped pages are still kept in inactive list.
> >>>
> >>>So my question is why we call mark_page_accessed() in 2.6.18 kernel, but don't
> >>>call it in 2.6.32 kernel.  Has any reason here?
> >>Behavior was changed in commit
> >>v2.6.28-6130-gbf3f3bc "mm: don't mark_page_accessed in fault path"
> >Thanks for pointing it out.
> >
> >>Please see also commits
> >>v3.2-4876-g34dbc67 "vmscan: promote shared file mapped pages" and
> >Yes, I will give it try.  If I understand correctly, this commit is
> >useful for multi-processes program that access a shared mmaped page,
> >but that could not be useful for us because our program is multi-thread.
> 
> What's the difference behavior between multi-processes and
> multi-thread in this case?

Hi Simon,

Sorry, I am not a MM expert.  IIUC, if we have two processes, this
mmaped page will be moved into active list.  But if we only have two
threads, reference_ptes == 1, and this mmaped page won't be moved into
active list.  Finally this page could be evicted.  Am I missing
something?

Thanks,
                                                - Zheng

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