memcg: synchronized LRU
A big patch for changing memcg's LRU semantics.
Now,
- page_cgroup is linked to mem_cgroup's its own LRU (per zone).
- LRU of page_cgroup is not synchronous with global LRU.
- page and page_cgroup is one-to-one and statically allocated.
- To find page_cgroup is on what LRU, you have to check pc->mem_cgroup as
- lru = page_cgroup_zoneinfo(pc, nid_of_pc, zid_of_pc);
- SwapCache is handled.
And, when we handle LRU list of page_cgroup, we do following.
pc = lookup_page_cgroup(page);
lock_page_cgroup(pc); .....................(1)
mz = page_cgroup_zoneinfo(pc);
spin_lock(&mz->lru_lock);
.....add to LRU
spin_unlock(&mz->lru_lock);
unlock_page_cgroup(pc);
But (1) is spin_lock and we have to be afraid of dead-lock with zone->lru_lock.
So, trylock() is used at (1), now. Without (1), we can't trust "mz" is correct.
This is a trial to remove this dirty nesting of locks.
This patch changes mz->lru_lock to be zone->lru_lock.
Then, above sequence will be written as
spin_lock(&zone->lru_lock); # in vmscan.c or swap.c via global LRU
mem_cgroup_add/remove/etc_lru() {
pc = lookup_page_cgroup(page);
mz = page_cgroup_zoneinfo(pc);
if (PageCgroupUsed(pc)) {
....add to LRU
}
spin_lock(&zone->lru_lock); # in vmscan.c or swap.c via global LRU
This is much simpler.
(*) We're safe even if we don't take lock_page_cgroup(pc). Because..
1. When pc->mem_cgroup can be modified.
- at charge.
- at account_move().
2. at charge
the PCG_USED bit is not set before pc->mem_cgroup is fixed.
3. at account_move()
the page is isolated and not on LRU.
Pros.
- easy for maintenance.
- memcg can make use of laziness of pagevec.
- we don't have to duplicated LRU/Active/Unevictable bit in page_cgroup.
- LRU status of memcg will be synchronized with global LRU's one.
- # of locks are reduced.
- account_move() is simplified very much.
Cons.
- may increase cost of LRU rotation.
(no impact if memcg is not configured.)
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Pavel Emelyanov <xemul@openvz.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/vmscan.c b/mm/vmscan.c
index f63b20d..45983af 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -512,7 +512,6 @@
lru = LRU_UNEVICTABLE;
add_page_to_unevictable_list(page);
}
- mem_cgroup_move_lists(page, lru);
/*
* page's status can change while we move it among lru. If an evictable
@@ -547,7 +546,6 @@
lru = !!TestClearPageActive(page) + page_is_file_cache(page);
lru_cache_add_lru(page, lru);
- mem_cgroup_move_lists(page, lru);
put_page(page);
}
#endif /* CONFIG_UNEVICTABLE_LRU */
@@ -813,6 +811,7 @@
return ret;
ret = -EBUSY;
+
if (likely(get_page_unless_zero(page))) {
/*
* Be careful not to clear PageLRU until after we're
@@ -821,6 +820,7 @@
*/
ClearPageLRU(page);
ret = 0;
+ mem_cgroup_del_lru(page);
}
return ret;
@@ -1134,7 +1134,6 @@
SetPageLRU(page);
lru = page_lru(page);
add_page_to_lru_list(zone, page, lru);
- mem_cgroup_move_lists(page, lru);
if (PageActive(page) && scan_global_lru(sc)) {
int file = !!page_is_file_cache(page);
zone->recent_rotated[file]++;
@@ -1263,7 +1262,7 @@
ClearPageActive(page);
list_move(&page->lru, &zone->lru[lru].list);
- mem_cgroup_move_lists(page, lru);
+ mem_cgroup_add_lru_list(page, lru);
pgmoved++;
if (!pagevec_add(&pvec, page)) {
__mod_zone_page_state(zone, NR_LRU_BASE + lru, pgmoved);
@@ -2408,6 +2407,7 @@
__dec_zone_state(zone, NR_UNEVICTABLE);
list_move(&page->lru, &zone->lru[l].list);
+ mem_cgroup_move_lists(page, LRU_UNEVICTABLE, l);
__inc_zone_state(zone, NR_INACTIVE_ANON + l);
__count_vm_event(UNEVICTABLE_PGRESCUED);
} else {
@@ -2416,6 +2416,7 @@
*/
SetPageUnevictable(page);
list_move(&page->lru, &zone->lru[LRU_UNEVICTABLE].list);
+ mem_cgroup_rotate_lru_list(page, LRU_UNEVICTABLE);
if (page_evictable(page, NULL))
goto retry;
}