linux-kernel - Re: [RFC 2/3] mm: make optimistic check for swapin readahead

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Date:	Mon, 15 Jun 2015 19:07:45 +0300
From:	Leon Romanovsky <leon@...n.nu>
To:	Rik van Riel <riel@...hat.com>
Cc:	Ebru Akagunduz <ebru.akagunduz@...il.com>,
	Linux-MM <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"kirill.shutemov" <kirill.shutemov@...ux.intel.com>,
	n-horiguchi <n-horiguchi@...jp.nec.com>,
	aarcange <aarcange@...hat.com>,
	"iamjoonsoo.kim" <iamjoonsoo.kim@....com>,
	Xiexiuqi <xiexiuqi@...wei.com>, gorcunov <gorcunov@...nvz.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Mel Gorman <mgorman@...e.de>, rientjes <rientjes@...gle.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	"aneesh.kumar" <aneesh.kumar@...ux.vnet.ibm.com>,
	Hugh Dickins <hughd@...gle.com>,
	Johannes Weiner <hannes@...xchg.org>, mhocko <mhocko@...e.cz>,
	boaz <boaz@...xistor.com>, raindel <raindel@...lanox.com>
Subject: Re: [RFC 2/3] mm: make optimistic check for swapin readahead

On Mon, Jun 15, 2015 at 5:05 PM, Rik van Riel <riel@...hat.com> wrote:
>
> On 06/14/2015 11:04 AM, Ebru Akagunduz wrote:
> > This patch makes optimistic check for swapin readahead
> > to increase thp collapse rate. Before getting swapped
> > out pages to memory, checks them and allows up to a
> > certain number. It also prints out using tracepoints
> > amount of unmapped ptes.
> >
> > Signed-off-by: Ebru Akagunduz <ebru.akagunduz@...il.com>
>
> > @@ -2639,11 +2640,11 @@ static int khugepaged_scan_pmd(struct mm_struct *mm,
> >  {
> >       pmd_t *pmd;
> >       pte_t *pte, *_pte;
> > -     int ret = 0, none_or_zero = 0;
> > +     int ret = 0, none_or_zero = 0, unmapped = 0;
> >       struct page *page;
> >       unsigned long _address;
> >       spinlock_t *ptl;
> > -     int node = NUMA_NO_NODE;
> > +     int node = NUMA_NO_NODE, max_ptes_swap = HPAGE_PMD_NR/8;
> >       bool writable = false, referenced = false;
>
> This has the effect of only swapping in 4kB pages to form a THP
> if 7/8th of the THP is already resident in memory.
Thanks for clarifing it to me.
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