From: Mel Gorman <mel@csn.ul.ie>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Minchan Kim <minchan.kim@gmail.com>,
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: Fri, 2 Apr 2010 09:52:52 +0100 [thread overview]
Message-ID: <20100402085251.GD621@csn.ul.ie> (raw)
In-Reply-To: <20100402092150.dc4b54a0.kamezawa.hiroyu@jp.fujitsu.com>
On Fri, Apr 02, 2010 at 09:21:50AM +0900, KAMEZAWA Hiroyuki wrote:
> On Thu, 1 Apr 2010 18:36:41 +0100
> Mel Gorman <mel@csn.ul.ie> wrote:
>
> > > > ==
> > > > skip_remap = 0;
> > > > if (PageAnon(page)) {
> > > > rcu_read_lock();
> > > > if (!page_mapped(page)) {
> > > > if (!PageSwapCache(page))
> > > > goto rcu_unlock;
> > > > /*
> > > > * We can't convice this anon_vma is valid or not because
> > > > * !page_mapped(page). Then, we do migration(radix-tree replacement)
> > > > * but don't remap it which touches anon_vma in page->mapping.
> > > > */
> > > > skip_remap = 1;
> > > > goto skip_unmap;
> > > > } else {
> > > > anon_vma = page_anon_vma(page);
> > > > atomic_inc(&anon_vma->external_refcount);
> > > > }
> > > > }
> > > > .....copy page, radix-tree replacement,....
> > > >
> > >
> > > It's not enough.
> > > we uses remove_migration_ptes in move_to_new_page, too.
> > > We have to prevent it.
> > > We can check PageSwapCache(page) in move_to_new_page and then
> > > skip remove_migration_ptes.
> > >
> > > ex)
> > > static int move_to_new_page(....)
> > > {
> > > int swapcache = PageSwapCache(page);
> > > ...
> > > if (!swapcache)
> > > if(!rc)
> > > remove_migration_ptes
> > > else
> > > newpage->mapping = NULL;
> > > }
> > >
> >
> > This I agree with.
> >
> me, too.
>
>
> > I am not sure this race exists because the page is locked but a key
> > observation has been made - A page that is unmapped can be migrated if
> > it's PageSwapCache but it may not have a valid anon_vma. Hence, in the
> > !page_mapped case, the key is to not use anon_vma. How about the
> > following patch?
> >
>
> Seems good to me. But (see below)
>
>
> > ==== CUT HERE ====
> >
> > mm,migration: Allow the migration of PageSwapCache pages
> >
> > PageAnon pages that are unmapped may or may not have an anon_vma so are
> > not currently migrated. However, a swap cache page can be migrated and
> > fits this description. This patch identifies page swap caches and allows
> > them to be migrated but ensures that no attempt to made to remap the pages
> > would would potentially try to access an already freed anon_vma.
> >
> > Signed-off-by: Mel Gorman <mel@csn.ul.ie>
> >
> > diff --git a/mm/migrate.c b/mm/migrate.c
> > index 35aad2a..5d0218b 100644
> > --- a/mm/migrate.c
> > +++ b/mm/migrate.c
> > @@ -484,7 +484,8 @@ static int fallback_migrate_page(struct address_space *mapping,
> > * < 0 - error code
> > * == 0 - success
> > */
> > -static int move_to_new_page(struct page *newpage, struct page *page)
> > +static int move_to_new_page(struct page *newpage, struct page *page,
> > + int safe_to_remap)
> > {
> > struct address_space *mapping;
> > int rc;
> > @@ -519,10 +520,12 @@ static int move_to_new_page(struct page *newpage, struct page *page)
> > else
> > rc = fallback_migrate_page(mapping, newpage, page);
> >
> > - if (!rc)
> > - remove_migration_ptes(page, newpage);
> > - else
> > - newpage->mapping = NULL;
> > + if (safe_to_remap) {
> > + if (!rc)
> > + remove_migration_ptes(page, newpage);
> > + else
> > + newpage->mapping = NULL;
> > + }
> >
> if (rc)
> newpage->mapping = NULL;
> else if (safe_to_remap)
> remove_migrateion_ptes(page, newpage);
>
> Is better. Old code cleared newpage->mapping if rc!=0.
>
True, done.
--
Mel Gorman
Part-time Phd Student Linux Technology Center
University of Limerick IBM Dublin Software Lab
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
next prev parent reply other threads:[~2010-04-02 8:53 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
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 [this message]
2010-04-01 9:30 ` Mel Gorman
2010-04-01 10:42 ` Minchan Kim
-- strict thread matches above, loose matches on Subject: below --
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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20100402085251.GD621@csn.ul.ie \
--to=mel@csn.ul.ie \
--cc=aarcange@redhat.com \
--cc=agl@us.ibm.com \
--cc=akpm@linux-foundation.org \
--cc=avi@redhat.com \
--cc=cl@linux-foundation.org \
--cc=kamezawa.hiroyu@jp.fujitsu.com \
--cc=kosaki.motohiro@jp.fujitsu.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=minchan.kim@gmail.com \
--cc=riel@redhat.com \
--cc=rientjes@google.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).