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SubjectRe: [patch 06/11] mm: memcg: remove optimization of keeping the root_mem_cgroup LRU lists empty
On Mon 12-09-11 12:57:23, Johannes Weiner wrote:
> 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.

Nevertheless we still do not charge them so this should be mentioned
here?

>
> The overhead is temporary until the double-LRU scheme is going away
> completely.
>
> Signed-off-by: Johannes Weiner <jweiner@redhat.com>

Reviewed-by: Michal Hocko <mhocko@suse.cz>

> ---
> mm/memcontrol.c | 12 ++----------
> 1 files changed, 2 insertions(+), 10 deletions(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 413e1f8..518f640 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -956,8 +956,6 @@ 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);
> }
> @@ -982,13 +980,11 @@ 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]);
> }
> @@ -1002,13 +998,11 @@ 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]);
> }
> @@ -1040,8 +1034,6 @@ 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]);
> }
>
> --
> 1.7.6
>
> --
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--
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9
Czech Republic


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