Re: [PATCH -mmotm-2009-12-10-17-19] Fix wrong rss count of smaps

[Minchan Kim]

Hi, Matt. 

On Tue, 29 Dec 2009 14:08:59 -0600
Matt Mackall <mpm@xxxxxxxxxxx> wrote:

> On Mon, 2009-12-28 at 13:46 +0900, Minchan Kim wrote:
> > I am not sure we have to account zero page with file_rss. 
> > Hugh and Kame's new zero page doesn't do it. 
> > As side effect of this, we can prevent innocent process which have a lot
> > of zero page when OOM happens. 
> > (But I am not sure there is a process like this :)
> > So I think not file_rss counting is not bad. 
> > 
> > RSS counting zero page with file_rss helps any program using smaps?
> > If we have to keep the old behavior, I have to remake this patch. 
> > 
> > == CUT_HERE ==
> > 
> > Long time ago, We regards zero page as file_rss and
> > vm_normal_page doesn't return NULL.
> > 
> > But now, we reinstated ZERO_PAGE and vm_normal_page's implementation
> > can return NULL in case of zero page. Also we don't count it with
> > file_rss any more.
> > 
> > Then, RSS and PSS can't be matched.
> > For consistency, Let's ignore zero page in smaps_pte_range.
> > 
> 
> Not counting the zero page in RSS is fine with me. But will this patch
> make the total from smaps agree with get_mm_rss()?

Yes. Anon page fault handler also don't count zero page any more, now. 
Nonetheless, smaps counts it with resident. 

It's point of this patch. 

But I reposted both anon fault handler and here counts it as file_rss
as compatibility with old zero page counting.
Pz, Look at that. :)

> 
> Regarding OOM handling: arguably RSS should play no role in OOM as it's
> practically meaningless in a shared memory system. If we were instead

It's very arguable issue for us that OOM depens on RSS.

> used per-process unshared pages as the metric (aka USS), we'd have a
> much better notion of how much memory an OOM kill would recover.
> Unfortunately, that's not trivial to track as the accounting on COW
> operations is not lightweight.

I think we can approximate it with the size of VM_SHARED vma of process
when VM calculate badness. 
What do you think about it?

Thanks for good idea, Matt. 

> 
> > CC: Matt Mackall <mpm@xxxxxxxxxxx>
> > Signed-off-by: Minchan Kim <minchan.kim@xxxxxxxxx>
> > ---
> >  fs/proc/task_mmu.c |    3 +--
> >  1 files changed, 1 insertions(+), 2 deletions(-)
> > 
> > diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> > index 47c03f4..f277c4a 100644
> > --- a/fs/proc/task_mmu.c
> > +++ b/fs/proc/task_mmu.c
> > @@ -361,12 +361,11 @@ static int smaps_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
> >  		if (!pte_present(ptent))
> >  			continue;
> >  
> > -		mss->resident += PAGE_SIZE;
> > -
> >  		page = vm_normal_page(vma, addr, ptent);
> >  		if (!page)
> >  			continue;
> >  
> > +		mss->resident += PAGE_SIZE;
> >  		/* Accumulate the size in pages that have been accessed. */
> >  		if (pte_young(ptent) || PageReferenced(page))
> >  			mss->referenced += PAGE_SIZE;
> > -- 
> > 1.5.6.3
> > 
> > 
> > 
> 
> 
> 
> -- 
> http://selenic.com : development and support for Mercurial and Linux
> 
> 


-- 
Kind regards,
Minchan Kim
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