linux-kernel - Re: [PATCH 16/19] thp: update documentation

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Date:	Wed, 19 Nov 2014 15:11:37 +0200
From:	"Kirill A. Shutemov" <kirill@...temov.name>
To:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
Cc:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Dave Hansen <dave.hansen@...el.com>,
	Hugh Dickins <hughd@...gle.com>, Mel Gorman <mgorman@...e.de>,
	Rik van Riel <riel@...hat.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Christoph Lameter <cl@...two.org>,
	Steve Capper <steve.capper@...aro.org>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...e.cz>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [PATCH 16/19] thp: update documentation

On Wed, Nov 19, 2014 at 08:07:59AM +0000, Naoya Horiguchi wrote:
> On Wed, Nov 05, 2014 at 04:49:51PM +0200, Kirill A. Shutemov wrote:
> > The patch updates Documentation/vm/transhuge.txt to reflect changes in
> > THP design.
> > 
> > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> > ---
> >  Documentation/vm/transhuge.txt | 84 +++++++++++++++++++-----------------------
> >  1 file changed, 38 insertions(+), 46 deletions(-)
> > 
> > diff --git a/Documentation/vm/transhuge.txt b/Documentation/vm/transhuge.txt
> > index df1794a9071f..33465e7b0d9b 100644
> > --- a/Documentation/vm/transhuge.txt
> > +++ b/Documentation/vm/transhuge.txt
> > @@ -200,9 +200,18 @@ thp_collapse_alloc_failed is incremented if khugepaged found a range
> >  	of pages that should be collapsed into one huge page but failed
> >  	the allocation.
> >  
> > -thp_split is incremented every time a huge page is split into base
> > +thp_split_page is incremented every time a huge page is split into base
> >  	pages. This can happen for a variety of reasons but a common
> >  	reason is that a huge page is old and is being reclaimed.
> > +	This action implies splitting all PMD the page mapped with.
> > +
> > +thp_split_page_failed is is incremented if kernel fails to split huge
> 
> 'is' appears twice.
> 
> > +	page. This can happen if the page was pinned by somebody.
> > +
> > +thp_split_pmd is incremented every time a PMD split into table of PTEs.
> > +	This can happen, for instance, when application calls mprotect() or
> > +	munmap() on part of huge page. It doesn't split huge page, only
> > +	page table entry.
> >  
> >  thp_zero_page_alloc is incremented every time a huge zero page is
> >  	successfully allocated. It includes allocations which where
> 
> There is a sentense related to the adjustment on futex code you just
> removed in patch 15/19 in "get_user_pages and follow_page" section.
> 
>   ...
>   split_huge_page() to avoid the head and tail pages to disappear from
>   under it, see the futex code to see an example of that, hugetlbfs also
>   needed special handling in futex code for similar reasons).
> 
> this seems obsolete, so we need some change on this?

I'll update documentation futher once patchset will be closer to ready
state.

-- 
 Kirill A. Shutemov
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