linux-kernel - RE: [patch] mm, thp: count thp_fault

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Date:	Thu, 22 Aug 2013 14:11:48 +0300 (EEST)
From:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:	David Rientjes <rientjes@...gle.com>
Cc:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>,
	Andrea Arcangeli <aarcange@...hat.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: RE: [patch] mm, thp: count thp_fault_fallback anytime thp fault fails

David Rientjes wrote:
> On Wed, 21 Aug 2013, Kirill A. Shutemov wrote:
> 
> > David Rientjes wrote:
> > > Currently, thp_fault_fallback in vmstat only gets incremented if a
> > > hugepage allocation fails.  If current's memcg hits its limit or the page
> > > fault handler returns an error, it is incorrectly accounted as a
> > > successful thp_fault_alloc.
> > > 
> > > Count thp_fault_fallback anytime the page fault handler falls back to
> > > using regular pages and only count thp_fault_alloc when a hugepage has
> > > actually been faulted.
> > > 
> > > Signed-off-by: David Rientjes <rientjes@...gle.com>
> > 
> > It's probably a good idea, but please make the behaviour consistent in
> > do_huge_pmd_wp_page() and collapse path, otherwise it doesn't make sense.
> > 
> 
> The collapse path has no fallback, the allocation either succeeds or it 
> fails.

THP_COLLAPSE_ALLOC should be counted after successful memcg charge or even
only after successful collapse.

-- 
 Kirill A. Shutemov
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