mm: memcg: remove optimization of keeping the root_mem_cgroup LRU lists empty

root_mem_cgroup, lacking a configurable limit, was never subject to
limit reclaim, so the pages charged to it could be kept off its LRU
lists.  They would be found on the global per-zone LRU lists upon
physical memory pressure and it made sense to avoid uselessly linking
them to both lists.

The global per-zone LRU lists are about to go away on memcg-enabled
kernels, with all pages being exclusively linked to their respective
per-memcg LRU lists.  As a result, pages of the root_mem_cgroup must
also be linked to its LRU lists again.  This is purely about the LRU
list, root_mem_cgroup is still not charged.

The overhead is temporary until the double-LRU scheme is going away
completely.

Signed-off-by: Johannes Weiner <[email protected]>
Reviewed-by: KAMEZAWA Hiroyuki <[email protected]>
Reviewed-by: Michal Hocko <[email protected]>
Reviewed-by: Kirill A. Shutemov <[email protected]>
Cc: Daisuke Nishimura <[email protected]>
Cc: Balbir Singh <[email protected]>
Cc: Ying Han <[email protected]>
Cc: Greg Thelen <[email protected]>
Cc: Michel Lespinasse <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Minchan Kim <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Cc: Hugh Dickins <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 750ed1449955885bfac56189075fe42ecee767fd..ad7f36f676ffbb7fdd9fa0545e89bcc02e153515 100644 (file)
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1031,8 +1031,6 @@ void mem_cgroup_del_lru_list(struct page *page, enum lru_list lru)
        mz = page_cgroup_zoneinfo(pc->mem_cgroup, page);
        /* huge page split is done under lru_lock. so, we have no races. */
        MEM_CGROUP_ZSTAT(mz, lru) -= 1 << compound_order(page);
-       if (mem_cgroup_is_root(pc->mem_cgroup))
-               return;
        VM_BUG_ON(list_empty(&pc->lru));
        list_del_init(&pc->lru);
 }
@@ -1057,13 +1055,11 @@ void mem_cgroup_rotate_reclaimable_page(struct page *page)
                return;
 
        pc = lookup_page_cgroup(page);
-       /* unused or root page is not rotated. */
+       /* unused page is not rotated. */
        if (!PageCgroupUsed(pc))
                return;
        /* Ensure pc->mem_cgroup is visible after reading PCG_USED. */
        smp_rmb();
-       if (mem_cgroup_is_root(pc->mem_cgroup))
-               return;
        mz = page_cgroup_zoneinfo(pc->mem_cgroup, page);
        list_move_tail(&pc->lru, &mz->lists[lru]);
 }
@@ -1077,13 +1073,11 @@ void mem_cgroup_rotate_lru_list(struct page *page, enum lru_list lru)
                return;
 
        pc = lookup_page_cgroup(page);
-       /* unused or root page is not rotated. */
+       /* unused page is not rotated. */
        if (!PageCgroupUsed(pc))
                return;
        /* Ensure pc->mem_cgroup is visible after reading PCG_USED. */
        smp_rmb();
-       if (mem_cgroup_is_root(pc->mem_cgroup))
-               return;
        mz = page_cgroup_zoneinfo(pc->mem_cgroup, page);
        list_move(&pc->lru, &mz->lists[lru]);
 }
@@ -1115,8 +1109,6 @@ void mem_cgroup_add_lru_list(struct page *page, enum lru_list lru)
        /* huge page split is done under lru_lock. so, we have no races. */
        MEM_CGROUP_ZSTAT(mz, lru) += 1 << compound_order(page);
        SetPageCgroupAcctLRU(pc);
-       if (mem_cgroup_is_root(pc->mem_cgroup))
-               return;
        list_add(&pc->lru, &mz->lists[lru]);
 }