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| author | Johannes Weiner <hannes@cmpxchg.org> | 2014-12-10 15:43:43 -0800 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2014-12-10 17:41:06 -0800 |
| commit | dfe0e773d0258a4d7dfd763e1fda04aa27680b90 (patch) | |
| tree | c1c18fcb86fe5fa24207eda5ba611d64eddf9e4d /mm/memcontrol.c | |
| parent | bc2f2e7ffe5b6292c74ee1206d6ca303e13886b2 (diff) | |
| download | linux-next-dfe0e773d0258a4d7dfd763e1fda04aa27680b90.tar.gz | |
mm: memcontrol: update mem_cgroup_page_lruvec() documentation
Commit 7512102cf64d ("memcg: fix GPF when cgroup removal races with last
exit") added a pc->mem_cgroup reset into mem_cgroup_page_lruvec() to
prevent a crash where an anon page gets uncharged on unmap, the memcg is
released, and then the final LRU isolation on free dereferences the
stale pc->mem_cgroup pointer.
But since commit 0a31bc97c80c ("mm: memcontrol: rewrite uncharge API"),
pages are only uncharged AFTER that final LRU isolation, which
guarantees the memcg's lifetime until then. pc->mem_cgroup now only
needs to be reset for swapcache readahead pages.
Update the comment and callsite requirements accordingly.
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Hugh Dickins <hughd@google.com>
Acked-by: Michal Hocko <mhocko@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/memcontrol.c')
| -rw-r--r-- | mm/memcontrol.c | 16 |
1 files changed, 8 insertions, 8 deletions
diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 975207a9cc65..b495f29d4746 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -1262,9 +1262,13 @@ out: } /** - * mem_cgroup_page_lruvec - return lruvec for adding an lru page + * mem_cgroup_page_lruvec - return lruvec for isolating/putting an LRU page * @page: the page * @zone: zone of the page + * + * This function is only safe when following the LRU page isolation + * and putback protocol: the LRU lock must be held, and the page must + * either be PageLRU() or the caller must have isolated/allocated it. */ struct lruvec *mem_cgroup_page_lruvec(struct page *page, struct zone *zone) { @@ -1282,13 +1286,9 @@ struct lruvec *mem_cgroup_page_lruvec(struct page *page, struct zone *zone) memcg = pc->mem_cgroup; /* - * Surreptitiously switch any uncharged offlist page to root: - * an uncharged page off lru does nothing to secure - * its former mem_cgroup from sudden removal. - * - * Our caller holds lru_lock, and PageCgroupUsed is updated - * under page_cgroup lock: between them, they make all uses - * of pc->mem_cgroup safe. + * Swapcache readahead pages are added to the LRU - and + * possibly migrated - before they are charged. Ensure + * pc->mem_cgroup is sane. */ if (!PageLRU(page) && !PageCgroupUsed(pc) && memcg != root_mem_cgroup) pc->mem_cgroup = memcg = root_mem_cgroup; |