[CCing Ingo for the memcg-devel vs tip/sched/numa inter tree dependency
- see bellow]
On Thu 05-07-12 02:44:53, Johannes Weiner wrote:
> Compaction (and page migration in general) can currently be hindered
> through pages being owned by memory cgroups that are at their limits
> and unreclaimable.
>
> The reason is that the replacement page is being charged against the
> limit while the page being replaced is also still charged. But this
> seems unnecessary, given that only one of the two pages will still be
> in use after migration finishes.
>
> This patch changes the memcg migration sequence so that the
> replacement page is not charged. Whatever page is still in use after
> successful or failed migration gets to keep the charge of the page
> that was going to be replaced.
Could you mention the side effect on the stat vs charges discrepancy,
please?
> Reported-by: David Rientjes <rientjes@xxxxxxxxxx>
> Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxx>
[...]
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 8137aea..aa06bf4 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
[...]
> @@ -1519,10 +1512,9 @@ migrate_misplaced_page(struct page *page, struct mm_struct *mm, int node)
> {
> struct page *oldpage = page, *newpage;
> struct address_space *mapping = page_mapping(page);
> - struct mem_cgroup *mcg;
> + struct mem_cgroup *memcg;
> unsigned int gfp;
> int rc = 0;
> - int charge = -ENOMEM;
>
> VM_BUG_ON(!PageLocked(page));
> VM_BUG_ON(page_mapcount(page));
> @@ -1556,12 +1548,7 @@ migrate_misplaced_page(struct page *page, struct mm_struct *mm, int node)
> if (!trylock_page(newpage))
> BUG(); /* new page should be unlocked!!! */
>
> - // XXX hnaz, is this right?
> - charge = mem_cgroup_prepare_migration(page, newpage, &mcg, gfp);
> - if (charge == -ENOMEM) {
> - rc = charge;
> - goto out;
> - }
> + mem_cgroup_prepare_migration(page, newpage, &memcg);
>
> newpage->index = page->index;
> newpage->mapping = page->mapping;
> @@ -1581,11 +1568,9 @@ migrate_misplaced_page(struct page *page, struct mm_struct *mm, int node)
> page = newpage;
> }
>
> + mem_cgroup_end_migration(memcg, oldpage, newpage, !rc);
> out:
> - if (!charge)
> - mem_cgroup_end_migration(mcg, oldpage, newpage, !rc);
> -
> - if (oldpage != page)
> + if (oldpage != page)
> put_page(oldpage);
>
> if (rc) {
Hmm, this depends on 4783af47 (mm: Migrate misplaced page) from
tip/sched/numa which adds an inter tree dependency which is quite
unfortunate from memcg-devel (aka mmotm git tree) tree POV.
I can cherry-pick this patch into memcg-devel but I am not sure what
is the merging status of the patch (XXX sounds like it is going to be
updated later). Ingo?
--
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9
Czech Republic
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