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Subject[PATCH v5] memcg: remove PCG_CACHE page_cgroup flag
On Wed, 25 Jan 2012 09:00:25 +0900
KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:

> On Tue, 24 Jan 2012 19:09:47 +0100
> Michal Hocko <mhocko@suse.cz> wrote:
>
> > On Tue 24-01-12 18:23:08, Michal Hocko wrote:
> > > On Tue 24-01-12 17:44:49, Johannes Weiner wrote:
> > > > On Tue, Jan 24, 2012 at 05:01:40PM +0100, Michal Hocko wrote:
> > > > > On Tue 24-01-12 15:54:11, Johannes Weiner wrote:
> > > > > > Hold on, I think this patch is still not complete: end_migration()
> > > > > > directly uses __mem_cgroup_uncharge_common() with the FORCE charge
> > > > > > type. This will uncharge all migrated anon pages as cache, when it
> > > > > > should decide based on PageAnon(used), which is the page where
> > > > > > ->mapping is intact after migration.
> > > > >
> > > > > You are right, I've missed that one as well. Anyway
> > > > > MEM_CGROUP_CHARGE_TYPE_FORCE is used only in mem_cgroup_end_migration
> > > > > these days and it got out of sync with its documentation (used by
> > > > > force_empty) quite some time ago (f817ed48). What about something like
> > > > > the following on top of the previous patch?
> > > > > ---
> > > > > Should be foldet into the previous patch with the updated changelog:
> > > > >
> > > > > Mapping of the unused page is not touched during migration (see
> > > >
> > > > used one, not unused. unused->mapping is globbered during migration.
> > >
> > > Yes, you are right:
> >
> > Sorry I haven't sent the most recent update. Here we go:
> > ---
> > Should be folded into the previous patch with the updated changelog:
> >
> Thanks, I'll fold this into v5.
> -Kame
>

v5 here
==
Subject: [PATCH v5] memcg: remove PCG_CACHE

We record 'the page is cache' by PCG_CACHE bit to page_cgroup.
Here, "CACHE" means anonymous user pages (and SwapCache). This
doesn't include shmem.

Consdering callers, at charge/uncharge, the caller should know
what the page is and we don't need to record it by using 1bit
per page.

This patch removes PCG_CACHE bit and make callers of
mem_cgroup_charge_statistics() to specify what the page is.

About page migration:
Mapping of the used page is not touched during migration (see
page_remove_rmap) so we can rely on it and push the correct charge type
down to __mem_cgroup_uncharge_common from end_migration for unused page.
The force flag was misleading was abused for skipping the needless
page_mapped() / PageCgroupMigration() check, as we know the unused page
is no longer mapped and cleared the migration flag just a few lines
up. But doing the checks is no biggie and it's not worth adding another
flag just to skip them.

Changelog since v4
- fixed a bug at page migration by Michal Hokko.

Changelog since v3
- renamed a variable 'rss' to 'anon'

Changelog since v2
- removed 'not_rss', added 'anon'
- changed a meaning of arguments to mem_cgroup_charge_statisitcs()
- removed a patch to mem_cgroup_uncharge_cache
- simplified comment.

Changelog since RFC.
- rebased onto memcg-devel
- rename 'file' to 'not_rss'
- some cleanup and added comment.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
---
include/linux/page_cgroup.h | 8 +-----
mm/memcontrol.c | 57 ++++++++++++++++++++++++-------------------
2 files changed, 33 insertions(+), 32 deletions(-)

diff --git a/include/linux/page_cgroup.h b/include/linux/page_cgroup.h
index a2d1177..1060292 100644
--- a/include/linux/page_cgroup.h
+++ b/include/linux/page_cgroup.h
@@ -4,7 +4,6 @@
enum {
/* flags for mem_cgroup */
PCG_LOCK, /* Lock for pc->mem_cgroup and following bits. */
- PCG_CACHE, /* charged as cache */
PCG_USED, /* this object is in use. */
PCG_MIGRATION, /* under page migration */
/* flags for mem_cgroup and file and I/O status */
@@ -64,11 +63,6 @@ static inline void ClearPageCgroup##uname(struct page_cgroup *pc) \
static inline int TestClearPageCgroup##uname(struct page_cgroup *pc) \
{ return test_and_clear_bit(PCG_##lname, &pc->flags); }

-/* Cache flag is set only once (at allocation) */
-TESTPCGFLAG(Cache, CACHE)
-CLEARPCGFLAG(Cache, CACHE)
-SETPCGFLAG(Cache, CACHE)
-
TESTPCGFLAG(Used, USED)
CLEARPCGFLAG(Used, USED)
SETPCGFLAG(Used, USED)
@@ -85,7 +79,7 @@ static inline void lock_page_cgroup(struct page_cgroup *pc)
{
/*
* Don't take this lock in IRQ context.
- * This lock is for pc->mem_cgroup, USED, CACHE, MIGRATION
+ * This lock is for pc->mem_cgroup, USED, MIGRATION
*/
bit_spin_lock(PCG_LOCK, &pc->flags);
}
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 1c56c5f..45dab06 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -670,15 +670,19 @@ static unsigned long mem_cgroup_read_events(struct mem_cgroup *memcg,
}

static void mem_cgroup_charge_statistics(struct mem_cgroup *memcg,
- bool file, int nr_pages)
+ bool anon, int nr_pages)
{
preempt_disable();

- if (file)
- __this_cpu_add(memcg->stat->count[MEM_CGROUP_STAT_CACHE],
+ /*
+ * Here, RSS means 'mapped anon' and anon's SwapCache. Shmem/tmpfs is
+ * counted as CACHE even if it's on ANON LRU.
+ */
+ if (anon)
+ __this_cpu_add(memcg->stat->count[MEM_CGROUP_STAT_RSS],
nr_pages);
else
- __this_cpu_add(memcg->stat->count[MEM_CGROUP_STAT_RSS],
+ __this_cpu_add(memcg->stat->count[MEM_CGROUP_STAT_CACHE],
nr_pages);

/* pagein of a big page is an event. So, ignore page size */
@@ -2405,6 +2409,8 @@ static void __mem_cgroup_commit_charge(struct mem_cgroup *memcg,
struct page_cgroup *pc,
enum charge_type ctype)
{
+ bool anon;
+
lock_page_cgroup(pc);
if (unlikely(PageCgroupUsed(pc))) {
unlock_page_cgroup(pc);
@@ -2424,21 +2430,14 @@ static void __mem_cgroup_commit_charge(struct mem_cgroup *memcg,
* See mem_cgroup_add_lru_list(), etc.
*/
smp_wmb();
- switch (ctype) {
- case MEM_CGROUP_CHARGE_TYPE_CACHE:
- case MEM_CGROUP_CHARGE_TYPE_SHMEM:
- SetPageCgroupCache(pc);
- SetPageCgroupUsed(pc);
- break;
- case MEM_CGROUP_CHARGE_TYPE_MAPPED:
- ClearPageCgroupCache(pc);
- SetPageCgroupUsed(pc);
- break;
- default:
- break;
- }

- mem_cgroup_charge_statistics(memcg, PageCgroupCache(pc), nr_pages);
+ SetPageCgroupUsed(pc);
+ if (ctype == MEM_CGROUP_CHARGE_TYPE_MAPPED)
+ anon = true;
+ else
+ anon = false;
+
+ mem_cgroup_charge_statistics(memcg, anon, nr_pages);
unlock_page_cgroup(pc);
WARN_ON_ONCE(PageLRU(page));
/*
@@ -2503,6 +2502,7 @@ static int mem_cgroup_move_account(struct page *page,
{
unsigned long flags;
int ret;
+ bool anon = PageAnon(page);

VM_BUG_ON(from == to);
VM_BUG_ON(PageLRU(page));
@@ -2531,14 +2531,14 @@ static int mem_cgroup_move_account(struct page *page,
__this_cpu_inc(to->stat->count[MEM_CGROUP_STAT_FILE_MAPPED]);
preempt_enable();
}
- mem_cgroup_charge_statistics(from, PageCgroupCache(pc), -nr_pages);
+ mem_cgroup_charge_statistics(from, anon, -nr_pages);
if (uncharge)
/* This is not "cancel", but cancel_charge does all we need. */
__mem_cgroup_cancel_charge(from, nr_pages);

/* caller should have done css_get */
pc->mem_cgroup = to;
- mem_cgroup_charge_statistics(to, PageCgroupCache(pc), nr_pages);
+ mem_cgroup_charge_statistics(to, anon, nr_pages);
/*
* We charges against "to" which may not have any tasks. Then, "to"
* can be under rmdir(). But in current implementation, caller of
@@ -2884,6 +2884,7 @@ __mem_cgroup_uncharge_common(struct page *page, enum charge_type ctype)
struct mem_cgroup *memcg = NULL;
unsigned int nr_pages = 1;
struct page_cgroup *pc;
+ bool anon;

if (mem_cgroup_disabled())
return NULL;
@@ -2915,6 +2916,7 @@ __mem_cgroup_uncharge_common(struct page *page, enum charge_type ctype)
/* See mem_cgroup_prepare_migration() */
if (page_mapped(page) || PageCgroupMigration(pc))
goto unlock_out;
+ anon = true;
break;
case MEM_CGROUP_CHARGE_TYPE_SWAPOUT:
if (!PageAnon(page)) { /* Shared memory */
@@ -2922,12 +2924,14 @@ __mem_cgroup_uncharge_common(struct page *page, enum charge_type ctype)
goto unlock_out;
} else if (page_mapped(page)) /* Anon */
goto unlock_out;
+ anon = true;
break;
default:
+ anon = false;
break;
}

- mem_cgroup_charge_statistics(memcg, PageCgroupCache(pc), -nr_pages);
+ mem_cgroup_charge_statistics(memcg, anon, -nr_pages);

ClearPageCgroupUsed(pc);
/*
@@ -3251,6 +3255,7 @@ void mem_cgroup_end_migration(struct mem_cgroup *memcg,
{
struct page *used, *unused;
struct page_cgroup *pc;
+ bool anon;

if (!memcg)
return;
@@ -3272,8 +3277,10 @@ void mem_cgroup_end_migration(struct mem_cgroup *memcg,
lock_page_cgroup(pc);
ClearPageCgroupMigration(pc);
unlock_page_cgroup(pc);
-
- __mem_cgroup_uncharge_common(unused, MEM_CGROUP_CHARGE_TYPE_FORCE);
+ anon = PageAnon(used);
+ __mem_cgroup_uncharge_common(unused,
+ anon ? MEM_CGROUP_CHARGE_TYPE_MAPPED
+ : MEM_CGROUP_CHARGE_TYPE_CACHE);

/*
* If a page is a file cache, radix-tree replacement is very atomic
@@ -3283,7 +3290,7 @@ void mem_cgroup_end_migration(struct mem_cgroup *memcg,
* and USED bit check in mem_cgroup_uncharge_page() will do enough
* check. (see prepare_charge() also)
*/
- if (PageAnon(used))
+ if (anon)
mem_cgroup_uncharge_page(used);
/*
* At migration, we may charge account against cgroup which has no
@@ -3313,7 +3320,7 @@ void mem_cgroup_replace_page_cache(struct page *oldpage,
/* fix accounting on old pages */
lock_page_cgroup(pc);
memcg = pc->mem_cgroup;
- mem_cgroup_charge_statistics(memcg, PageCgroupCache(pc), -1);
+ mem_cgroup_charge_statistics(memcg, false, -1);
ClearPageCgroupUsed(pc);
unlock_page_cgroup(pc);

--
1.7.4.1




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