linux-kernel - Re: [PATCH 3/7] khugepaged: Drain LRU add pagevec to get rid of extra pins

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Date:   Sat, 28 Mar 2020 03:20:41 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Zi Yan <ziy@...dia.com>
Cc:     akpm@...ux-foundation.org, Andrea Arcangeli <aarcange@...hat.com>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCH 3/7] khugepaged: Drain LRU add pagevec to get rid of
 extra pins

On Fri, Mar 27, 2020 at 01:34:20PM -0400, Zi Yan wrote:
> On 27 Mar 2020, at 13:05, Kirill A. Shutemov wrote:
> 
> > __collapse_huge_page_isolate() may fail due to extra pin in the LRU add
> > pagevec. It's petty common for swapin case: we swap in pages just to
> > fail due to the extra pin.
> >
> > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> > ---
> >  mm/khugepaged.c | 8 ++++++++
> >  1 file changed, 8 insertions(+)
> >
> > diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> > index 14d7afc90786..39e0994abeb8 100644
> > --- a/mm/khugepaged.c
> > +++ b/mm/khugepaged.c
> > @@ -585,11 +585,19 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
> >  		 * The page must only be referenced by the scanned process
> >  		 * and page swap cache.
> >  		 */
> > +		if (page_count(page) != 1 + PageSwapCache(page)) {
> > +			/*
> > +			 * Drain pagevec and retry just in case we can get rid
> > +			 * of the extra pin, like in swapin case.
> > +			 */
> > +			lru_add_drain();
> > +		}
> >  		if (page_count(page) != 1 + PageSwapCache(page)) {
> >  			unlock_page(page);
> >  			result = SCAN_PAGE_COUNT;
> >  			goto out;
> >  		}
> > +
> >  		if (pte_write(pteval)) {
> >  			writable = true;
> >  		} else {
> > -- 
> > 2.26.0
> 
> Looks good to me. Is the added empty line intentional?

Yes. It groups try and retry together.

-- 
 Kirill A. Shutemov