From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
To: Minchan Kim <minchan.kim@gmail.com>
Cc: Mel Gorman <mel@csn.ul.ie>,
Andrew Morton <akpm@linux-foundation.org>,
Andrea Arcangeli <aarcange@redhat.com>,
Christoph Lameter <cl@linux-foundation.org>,
Adam Litke <agl@us.ibm.com>, Avi Kivity <avi@redhat.com>,
David Rientjes <rientjes@google.com>,
KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
Rik van Riel <riel@redhat.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH 14/14] mm,migration: Allow the migration of PageSwapCache pages
Date: Thu, 1 Apr 2010 12:01:23 +0900 [thread overview]
Message-ID: <20100401120123.f9f9e872.kamezawa.hiroyu@jp.fujitsu.com> (raw)
In-Reply-To: <j2s28c262361003311943ke6d39007of3861743cef3733a@mail.gmail.com>
On Thu, 1 Apr 2010 11:43:18 +0900
Minchan Kim <minchan.kim@gmail.com> wrote:
> On Wed, Mar 31, 2010 at 2:26 PM, KAMEZAWA Hiroyuki A A A /*
> >> diff --git a/mm/rmap.c b/mm/rmap.c
> >> index af35b75..d5ea1f2 100644
> >> --- a/mm/rmap.c
> >> +++ b/mm/rmap.c
> >> @@ -1394,9 +1394,11 @@ int rmap_walk(struct page *page, int (*rmap_one)(struct page *,
> >>
> >> A A A if (unlikely(PageKsm(page)))
> >> A A A A A A A return rmap_walk_ksm(page, rmap_one, arg);
> >> - A A else if (PageAnon(page))
> >> + A A else if (PageAnon(page)) {
> >> + A A A A A A if (PageSwapCache(page))
> >> + A A A A A A A A A A return SWAP_AGAIN;
> >> A A A A A A A return rmap_walk_anon(page, rmap_one, arg);
> >
> > SwapCache has a condition as (PageSwapCache(page) && page_mapped(page) == true.
> >
>
> In case of tmpfs, page has swapcache but not mapped.
>
> > Please see do_swap_page(), PageSwapCache bit is cleared only when
> >
> > do_swap_page()...
> > A A A swap_free(entry);
> > A A A A if (vm_swap_full() || (vma->vm_flags & VM_LOCKED) || PageMlocked(page))
> > A A A A A A A A try_to_free_swap(page);
> >
> > Then, PageSwapCache is cleared only when swap is freeable even if mapped.
> >
> > rmap_walk_anon() should be called and the check is not necessary.
>
> Frankly speaking, I don't understand what is Mel's problem, why he added
> Swapcache check in rmap_walk, and why do you said we don't need it.
>
> Could you explain more detail if you don't mind?
>
I may miss something.
unmap_and_move()
1. try_to_unmap(TTU_MIGRATION)
2. move_to_newpage
3. remove_migration_ptes
-> rmap_walk()
Then, to map a page back we unmapped we call rmap_walk().
Assume a SwapCache which is mapped, then, PageAnon(page) == true.
At 1. try_to_unmap() will rewrite pte with swp_entry of SwapCache.
mapcount goes to 0.
At 2. SwapCache is copied to a new page.
At 3. The new page is mapped back to the place. Now, newpage's mapcount is 0.
Before patch, the new page is mapped back to all ptes.
After patch, the new page is not mapped back because its mapcount is 0.
I don't think shared SwapCache of anon is not an usual behavior, so, the logic
before patch is more attractive.
If SwapCache is not mapped before "1", we skip "1" and rmap_walk will do nothing
because page->mapping is NULL.
Thanks,
-Kame
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next prev parent reply other threads:[~2010-04-01 3:05 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-03-30 9:14 [PATCH 0/14] Memory Compaction v6 Mel Gorman
2010-03-30 9:14 ` [PATCH 01/14] mm,migration: Take a reference to the anon_vma before migrating Mel Gorman
2010-03-30 9:14 ` [PATCH 02/14] mm,migration: Do not try to migrate unmapped anonymous pages Mel Gorman
2010-03-30 9:14 ` [PATCH 03/14] mm: Share the anon_vma ref counts between KSM and page migration Mel Gorman
2010-03-30 9:14 ` [PATCH 04/14] Allow CONFIG_MIGRATION to be set without CONFIG_NUMA or memory hot-remove Mel Gorman
2010-03-30 9:14 ` [PATCH 05/14] Export unusable free space index via /proc/unusable_index Mel Gorman
2010-03-30 9:14 ` [PATCH 06/14] Export fragmentation index via /proc/extfrag_index Mel Gorman
2010-03-30 9:14 ` [PATCH 07/14] Move definition for LRU isolation modes to a header Mel Gorman
2010-03-30 9:14 ` [PATCH 08/14] Memory compaction core Mel Gorman
2010-03-30 9:14 ` [PATCH 09/14] Add /proc trigger for memory compaction Mel Gorman
2010-03-30 9:14 ` [PATCH 10/14] Add /sys trigger for per-node " Mel Gorman
2010-03-30 9:14 ` [PATCH 11/14] Direct compact when a high-order allocation fails Mel Gorman
2010-03-30 9:14 ` [PATCH 12/14] Add a tunable that decides when memory should be compacted and when it should be reclaimed Mel Gorman
2010-03-30 9:14 ` [PATCH 13/14] Do not compact within a preferred zone after a compaction failure Mel Gorman
2010-03-30 9:14 ` [PATCH 14/14] mm,migration: Allow the migration of PageSwapCache pages Mel Gorman
2010-03-31 5:26 ` KAMEZAWA Hiroyuki
2010-03-31 11:27 ` Mel Gorman
2010-03-31 23:57 ` KAMEZAWA Hiroyuki
2010-04-01 2:39 ` Minchan Kim
2010-04-01 2:43 ` Minchan Kim
2010-04-01 3:01 ` KAMEZAWA Hiroyuki [this message]
2010-04-01 4:44 ` Minchan Kim
2010-04-01 5:42 ` KAMEZAWA Hiroyuki
2010-04-01 10:51 ` Minchan Kim
2010-04-01 17:36 ` Mel Gorman
2010-04-02 0:20 ` Minchan Kim
2010-04-02 8:51 ` Mel Gorman
2010-04-02 0:21 ` KAMEZAWA Hiroyuki
2010-04-02 8:52 ` Mel Gorman
2010-04-01 9:30 ` Mel Gorman
2010-04-01 10:42 ` Minchan Kim
2010-04-02 16:02 [PATCH 0/14] Memory Compaction v7 Mel Gorman
2010-04-02 16:02 ` [PATCH 14/14] mm,migration: Allow the migration of PageSwapCache pages Mel Gorman
2010-04-06 6:54 ` KAMEZAWA Hiroyuki
2010-04-06 15:37 ` Minchan Kim
2010-04-07 0:06 ` Andrew Morton
2010-04-07 16:49 ` Mel Gorman
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