linux-kernel - Re: [PATCHv2 4/8] khugepaged: Drain LRU add pagevec after swapin

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Message-ID: <20200408130532.ktztqf5fabo3x3cd@box>
Date:   Wed, 8 Apr 2020 16:05:32 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Yang Shi <yang.shi@...ux.alibaba.com>
Cc:     akpm@...ux-foundation.org, Andrea Arcangeli <aarcange@...hat.com>,
        Zi Yan <ziy@...dia.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCHv2 4/8] khugepaged: Drain LRU add pagevec after swapin

On Mon, Apr 06, 2020 at 11:29:11AM -0700, Yang Shi wrote:
> 
> 
> On 4/3/20 4:29 AM, 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.
> > 
> > Drain LRU add pagevec on sucessfull swapin.
> > 
> > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> > ---
> >   mm/khugepaged.c | 5 +++++
> >   1 file changed, 5 insertions(+)
> > 
> > diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> > index fdc10ffde1ca..57ff287caf6b 100644
> > --- a/mm/khugepaged.c
> > +++ b/mm/khugepaged.c
> > @@ -940,6 +940,11 @@ static bool __collapse_huge_page_swapin(struct mm_struct *mm,
> >   	}
> >   	vmf.pte--;
> >   	pte_unmap(vmf.pte);
> > +
> > +	/* Drain LRU add pagevec to remove extra pin on the swapped in pages */
> > +	if (swapped_in)
> > +		lru_add_drain();
> 
> There is already lru_add_drain() called in swap readahead path, please see
> swap_vma_readahead() and swap_cluster_readahead().

But not for synchronous case. See SWP_SYNCHRONOUS_IO branch in
do_swap_page().

Maybe we should drain it in swap_readpage() or in do_swap_page() after
swap_readpage()? I donno.

-- 
 Kirill A. Shutemov