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

From: Leon Romanovsky <leon@leon.nu>
To: Rik van Riel <riel@redhat.com>
Cc: Ebru Akagunduz <ebru.akagunduz@gmail.com>,
	Linux-MM <linux-mm@kvack.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	"kirill.shutemov" <kirill.shutemov@linux.intel.com>,
	n-horiguchi <n-horiguchi@ah.jp.nec.com>,
	aarcange <aarcange@redhat.com>,
	"iamjoonsoo.kim" <iamjoonsoo.kim@lge.com>,
	Xiexiuqi <xiexiuqi@huawei.com>, gorcunov <gorcunov@openvz.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Mel Gorman <mgorman@suse.de>, rientjes <rientjes@google.com>,
	Vlastimil Babka <vbabka@suse.cz>,
	"aneesh.kumar" <aneesh.kumar@linux.vnet.ibm.com>,
	Hugh Dickins <hughd@google.com>,
	Johannes Weiner <hannes@cmpxchg.org>, mhocko <mhocko@suse.cz>,
	boaz <boaz@plexistor.com>, raindel <raindel@mellanox.com>
Subject: Re: [RFC 2/3] mm: make optimistic check for swapin readahead
Date: Mon, 15 Jun 2015 19:07:45 +0300	[thread overview]
Message-ID: <CALq1K=JhxwLf-pWSd0LJ6A45E-EZGYUhNaUQtpi6q4WRNGUBnQ@mail.gmail.com> (raw)
In-Reply-To: <557EDBA2.9090308@redhat.com>

On Mon, Jun 15, 2015 at 5:05 PM, Rik van Riel <riel@redhat.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@gmail.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.