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authorKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>2008-02-07 00:14:10 -0800
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2008-02-07 08:42:19 -0800
commitae41be374293e70e1ed441d986afcc6e744ef9d9 (patch)
treed8e2143820bbf3ed2f1f79ed99ee430284567b93 /mm
parent9175e0311ec9e6d1bf1f6dfecf9268baf08765e6 (diff)
downloadlwn-ae41be374293e70e1ed441d986afcc6e744ef9d9.tar.gz
lwn-ae41be374293e70e1ed441d986afcc6e744ef9d9.zip
bugfix for memory cgroup controller: migration under memory controller fix
While using memory control cgroup, page-migration under it works as following. == 1. uncharge all refs at try to unmap. 2. charge regs again remove_migration_ptes() == This is simple but has following problems. == The page is uncharged and charged back again if *mapped*. - This means that cgroup before migration can be different from one after migration - If page is not mapped but charged as page cache, charge is just ignored (because not mapped, it will not be uncharged before migration) This is memory leak. == This patch tries to keep memory cgroup at page migration by increasing one refcnt during it. 3 functions are added. mem_cgroup_prepare_migration() --- increase refcnt of page->page_cgroup mem_cgroup_end_migration() --- decrease refcnt of page->page_cgroup mem_cgroup_page_migration() --- copy page->page_cgroup from old page to new page. During migration - old page is under PG_locked. - new page is under PG_locked, too. - both old page and new page is not on LRU. These 3 facts guarantee that page_cgroup() migration has no race. Tested and worked well in x86_64/fake-NUMA box. Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Cc: Balbir Singh <balbir@linux.vnet.ibm.com> Cc: Pavel Emelianov <xemul@openvz.org> Cc: Paul Menage <menage@google.com> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: "Eric W. Biederman" <ebiederm@xmission.com> Cc: Nick Piggin <nickpiggin@yahoo.com.au> Cc: Kirill Korotaev <dev@sw.ru> Cc: Herbert Poetzl <herbert@13thfloor.at> Cc: David Rientjes <rientjes@google.com> Cc: Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm')
-rw-r--r--mm/memcontrol.c43
-rw-r--r--mm/migrate.c13
2 files changed, 53 insertions, 3 deletions
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 3270ce7375db..128f45c16fa6 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -492,6 +492,49 @@ void mem_cgroup_uncharge(struct page_cgroup *pc)
}
}
}
+/*
+ * Returns non-zero if a page (under migration) has valid page_cgroup member.
+ * Refcnt of page_cgroup is incremented.
+ */
+
+int mem_cgroup_prepare_migration(struct page *page)
+{
+ struct page_cgroup *pc;
+ int ret = 0;
+ lock_page_cgroup(page);
+ pc = page_get_page_cgroup(page);
+ if (pc && atomic_inc_not_zero(&pc->ref_cnt))
+ ret = 1;
+ unlock_page_cgroup(page);
+ return ret;
+}
+
+void mem_cgroup_end_migration(struct page *page)
+{
+ struct page_cgroup *pc = page_get_page_cgroup(page);
+ mem_cgroup_uncharge(pc);
+}
+/*
+ * We know both *page* and *newpage* are now not-on-LRU and Pg_locked.
+ * And no race with uncharge() routines because page_cgroup for *page*
+ * has extra one reference by mem_cgroup_prepare_migration.
+ */
+
+void mem_cgroup_page_migration(struct page *page, struct page *newpage)
+{
+ struct page_cgroup *pc;
+retry:
+ pc = page_get_page_cgroup(page);
+ if (!pc)
+ return;
+ if (clear_page_cgroup(page, pc) != pc)
+ goto retry;
+ pc->page = newpage;
+ lock_page_cgroup(newpage);
+ page_assign_page_cgroup(newpage, pc);
+ unlock_page_cgroup(newpage);
+ return;
+}
int mem_cgroup_write_strategy(char *buf, unsigned long long *tmp)
{
diff --git a/mm/migrate.c b/mm/migrate.c
index 763794144697..a73504ff5ab9 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -593,9 +593,10 @@ static int move_to_new_page(struct page *newpage, struct page *page)
else
rc = fallback_migrate_page(mapping, newpage, page);
- if (!rc)
+ if (!rc) {
+ mem_cgroup_page_migration(page, newpage);
remove_migration_ptes(page, newpage);
- else
+ } else
newpage->mapping = NULL;
unlock_page(newpage);
@@ -614,6 +615,7 @@ static int unmap_and_move(new_page_t get_new_page, unsigned long private,
int *result = NULL;
struct page *newpage = get_new_page(page, private, &result);
int rcu_locked = 0;
+ int charge = 0;
if (!newpage)
return -ENOMEM;
@@ -673,14 +675,19 @@ static int unmap_and_move(new_page_t get_new_page, unsigned long private,
goto rcu_unlock;
}
+ charge = mem_cgroup_prepare_migration(page);
/* Establish migration ptes or remove ptes */
try_to_unmap(page, 1);
if (!page_mapped(page))
rc = move_to_new_page(newpage, page);
- if (rc)
+ if (rc) {
remove_migration_ptes(page, page);
+ if (charge)
+ mem_cgroup_end_migration(page);
+ } else if (charge)
+ mem_cgroup_end_migration(newpage);
rcu_unlock:
if (rcu_locked)
rcu_read_unlock();