From: Minchan Kim <minchan.kim@gmail.com>
To: Mel Gorman <mgorman@suse.de>
Cc: Andrea Arcangeli <aarcange@redhat.com>,
Mel Gorman <mel@csn.ul.ie>,
akpm@linux-foundation.org, Ury Stankevich <urykhy@gmail.com>,
KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH] mm: compaction: Abort compaction if too many pages are isolated and caller is asynchronous
Date: Mon, 6 Jun 2011 23:01:20 +0900 [thread overview]
Message-ID: <20110606140120.GC1686@barrios-laptop> (raw)
In-Reply-To: <20110606101557.GA5247@suse.de>
On Mon, Jun 06, 2011 at 11:15:57AM +0100, Mel Gorman wrote:
> On Fri, Jun 03, 2011 at 08:01:44AM +0900, Minchan Kim wrote:
> > On Fri, Jun 3, 2011 at 7:32 AM, Andrea Arcangeli <aarcange@redhat.com> wrote:
> > > On Fri, Jun 03, 2011 at 07:23:48AM +0900, Minchan Kim wrote:
> > >> I mean we have more tail pages than head pages. So I think we are likely to
> > >> meet tail pages. Of course, compared to all pages(page cache, anon and
> > >> so on), compound pages would be very small percentage.
> > >
> > > Yes that's my point, that being a small percentage it's no big deal to
> > > break the loop early.
> >
> > Indeed.
> >
> > >
> > >> > isolated the head and it's useless to insist on more tail pages (at
> > >> > least for large page size like on x86). Plus we've compaction so
> > >>
> > >> I can't understand your point. Could you elaborate it?
> > >
> > > What I meant is that if we already isolated the head page of the THP,
> > > we don't need to try to free the tail pages and breaking the loop
> > > early, will still give us a chance to free a whole 2m because we
> > > isolated the head page (it'll involve some work and swapping but if it
> > > was a compoundtranspage we're ok to break the loop and we're not
> > > making the logic any worse). Provided the PMD_SIZE is quite large like
> > > 2/4m...
> >
> > Do you want this? (it's almost pseudo-code)
> >
> > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > index 7a4469b..9d7609f 100644
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -1017,7 +1017,7 @@ static unsigned long isolate_lru_pages(unsigned
> > long nr_to_scan,
> > for (scan = 0; scan < nr_to_scan && !list_empty(src); scan++) {
> > struct page *page;
> > unsigned long pfn;
> > - unsigned long end_pfn;
> > + unsigned long start_pfn, end_pfn;
> > unsigned long page_pfn;
> > int zone_id;
> >
> > @@ -1057,9 +1057,9 @@ static unsigned long isolate_lru_pages(unsigned
> > long nr_to_scan,
> > */
> > zone_id = page_zone_id(page);
> > page_pfn = page_to_pfn(page);
> > - pfn = page_pfn & ~((1 << order) - 1);
> > + start_pfn = pfn = page_pfn & ~((1 << order) - 1);
> > end_pfn = pfn + (1 << order);
> > - for (; pfn < end_pfn; pfn++) {
> > + while (pfn < end_pfn) {
> > struct page *cursor_page;
> >
> > /* The target page is in the block, ignore it. */
> > @@ -1086,17 +1086,25 @@ static unsigned long
> > isolate_lru_pages(unsigned long nr_to_scan,
> > break;
> >
> > if (__isolate_lru_page(cursor_page, mode, file) == 0) {
> > + int isolated_pages;
> > list_move(&cursor_page->lru, dst);
> > mem_cgroup_del_lru(cursor_page);
> > - nr_taken += hpage_nr_pages(page);
> > + isolated_pages = hpage_nr_pages(page);
> > + nr_taken += isolated_pages;
> > + /* if we isolated pages enough, let's
> > break early */
> > + if (nr_taken > end_pfn - start_pfn)
> > + break;
> > + pfn += isolated_pages;
>
> I think this condition is somewhat unlikely. We are scanning within
> aligned blocks in this linear scanner. Huge pages are always aligned
> so the only situation where we'll encounter a hugepage in the middle
> of this linear scan is when the requested order is larger than a huge
> page. This is exceptionally rare.
>
> Did I miss something?
Never. You're absolute right.
I don't have systems which have lots of hpages.
But I have heard some guys tunes MAX_ORDER(Whether it's a good or bad is off-topic).
Anyway, it would be good in such system but I admit it would be rare.
I don't have strong mind about this pseudo patch.
--
Kind regards
Minchan Kim
next prev parent reply other threads:[~2011-06-06 14:01 UTC|newest]
Thread overview: 63+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-05-30 13:13 [PATCH] mm: compaction: Abort compaction if too many pages are isolated and caller is asynchronous Mel Gorman
2011-05-30 14:31 ` Andrea Arcangeli
2011-05-30 15:37 ` Mel Gorman
2011-05-30 16:55 ` Mel Gorman
2011-05-30 17:53 ` Andrea Arcangeli
2011-05-31 12:16 ` Minchan Kim
2011-05-31 12:24 ` Andrea Arcangeli
2011-05-31 13:33 ` Minchan Kim
2011-05-31 14:14 ` Andrea Arcangeli
2011-05-31 14:37 ` Minchan Kim
2011-05-31 14:38 ` Minchan Kim
2011-06-02 18:23 ` Andrea Arcangeli
2011-06-02 20:21 ` Minchan Kim
2011-06-02 20:59 ` Minchan Kim
2011-06-02 22:03 ` Andrea Arcangeli
2011-06-02 21:40 ` Andrea Arcangeli
2011-06-02 22:23 ` Minchan Kim
2011-06-02 22:32 ` Andrea Arcangeli
2011-06-02 23:01 ` Minchan Kim
2011-06-03 17:37 ` Andrea Arcangeli
2011-06-03 18:07 ` Andrea Arcangeli
2011-06-04 7:59 ` Minchan Kim
2011-06-06 10:32 ` Mel Gorman
2011-06-06 12:49 ` Andrea Arcangeli
2011-06-06 14:47 ` Mel Gorman
2011-06-06 14:07 ` Minchan Kim
2011-06-06 10:15 ` Mel Gorman
2011-06-06 10:26 ` Mel Gorman
2011-06-06 14:01 ` Minchan Kim [this message]
2011-06-06 14:26 ` Minchan Kim
2011-06-02 23:02 ` Minchan Kim
2011-06-01 0:57 ` Mel Gorman
2011-06-01 9:24 ` Mel Gorman
2011-06-01 17:58 ` Mel Gorman
2011-06-01 19:15 ` Andrea Arcangeli
2011-06-01 21:40 ` Mel Gorman
2011-06-01 23:30 ` Andrea Arcangeli
2011-06-02 1:03 ` Mel Gorman
2011-06-02 8:34 ` Minchan Kim
2011-06-02 13:29 ` Andrea Arcangeli
2011-06-02 14:50 ` Mel Gorman
2011-06-02 15:37 ` Andrea Arcangeli
2011-06-03 2:09 ` Mel Gorman
2011-06-03 14:49 ` Mel Gorman
2011-06-03 15:45 ` Andrea Arcangeli
2011-06-04 7:25 ` Minchan Kim
2011-06-06 10:39 ` Mel Gorman
2011-06-06 12:38 ` Andrea Arcangeli
2011-06-06 14:55 ` Mel Gorman
2011-06-06 14:19 ` Minchan Kim
2011-06-06 22:32 ` Andrew Morton
2011-06-04 6:58 ` Minchan Kim
2011-06-06 10:43 ` Mel Gorman
2011-06-06 12:40 ` Andrea Arcangeli
2011-06-06 13:27 ` Minchan Kim
2011-06-06 13:23 ` Minchan Kim
2011-05-31 14:34 ` Mel Gorman
2011-05-30 14:45 ` [stable] " Greg KH
2011-05-30 16:14 ` Minchan Kim
2011-05-31 8:32 ` Mel Gorman
2011-05-31 4:48 ` KAMEZAWA Hiroyuki
2011-05-31 5:38 ` Minchan Kim
2011-05-31 7:14 ` KOSAKI Motohiro
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