Re: + mm-thp-avoid-unnecessary-swapin-in-khugepaged.patch added to -mm tree

From: Michal Hocko <mhocko@kernel.org>
To: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: akpm@linux-foundation.org, ebru.akagunduz@gmail.com,
	aarcange@redhat.com, aneesh.kumar@linux.vnet.ibm.com,
	boaz@plexistor.com, gorcunov@openvz.org, hannes@cmpxchg.org,
	hughd@google.com, iamjoonsoo.kim@lge.com,
	kirill.shutemov@linux.intel.com, mgorman@suse.de,
	n-horiguchi@ah.jp.nec.com, riel@redhat.com, rientjes@google.com,
	vbabka@suse.cz, mm-commits@vger.kernel.org, linux-mm@kvack.org
Subject: Re: + mm-thp-avoid-unnecessary-swapin-in-khugepaged.patch added to -mm tree
Date: Tue, 17 May 2016 14:25:21 +0200	[thread overview]
Message-ID: <20160517122520.GH14453@dhcp22.suse.cz> (raw)
In-Reply-To: <20160517113114.GC9540@node.shutemov.name>

On Tue 17-05-16 14:31:14, Kirill A. Shutemov wrote:
> On Tue, May 17, 2016 at 11:02:54AM +0200, Michal Hocko wrote:
[...]
> > ---
> > diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> > index 87f09dc986ab..1a4d4c807d92 100644
> > --- a/mm/huge_memory.c
> > +++ b/mm/huge_memory.c
> > @@ -2389,7 +2389,8 @@ static void __collapse_huge_page_swapin(struct mm_struct *mm,
> >  		swapped_in++;
> >  		ret = do_swap_page(mm, vma, _address, pte, pmd,
> >  				   FAULT_FLAG_ALLOW_RETRY|FAULT_FLAG_RETRY_NOWAIT,
> > -				   pteval);
> > +				   pteval,
> > +				   GFP_HIGHUSER_MOVABLE | ~__GFP_DIRECT_RECLAIM);
> 
> Why only direct recliam? I'm not sure if triggering kswapd is justified
> for swapin. Maybe ~__GFP_RECLAIM?

Dunno, skipping kswapd sounds like we might consume a lot of memory
and the next request might hit the direct reclaim too early. But this is
only a speculation. This has to be measured properly and evaluated
against real usecases.

-- 
Michal Hocko
SUSE Labs

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