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

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

On Sat, Apr 27, 2013 at 03:40:13PM +0800, Simon Jeons wrote:
> Hi Zheng,
> On 04/27/2013 03:55 PM, Zheng Liu wrote:
> >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?
> 
> Multi-threads will have same mm_struct and task_struct?

Multi-threads share one mm_struct and have different task_struct's.
Multi-processes have different mm_struct's and task_struct's.

Regards,
                                                - Zheng

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