Re: [patch 01/11] mm: memcg: fix compaction/migration failing due to memcg limits
From: Michal Hocko <hidden>
Date: 2012-07-09 14:15:59
Also in:
linux-mm, lkml
[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 <redacted> Signed-off-by: Johannes Weiner <redacted>
Acked-by: Michal Hocko <redacted> [...]
quoted hunk ↗ jump to hunk
diff --git a/mm/migrate.c b/mm/migrate.c index 8137aea..aa06bf4 100644 --- a/mm/migrate.c +++ b/mm/migrate.c
[...]
quoted hunk ↗ jump to hunk
@@ -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