Better explain re-entrant migration when compaction races with reclaim, and also mention swapcache readahead pages as possible uncharged migration sources. Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx> --- mm/memcontrol.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index fc1d7ca96b9d..76892eb89d26 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -6166,7 +6166,12 @@ void mem_cgroup_migrate(struct page *oldpage, struct page *newpage, if (PageCgroupUsed(pc)) return; - /* Re-entrant migration: old page already uncharged? */ + /* + * Swapcache readahead pages can get migrated before being + * charged, and migration from compaction can happen to an + * uncharged page when the PFN walker finds a page that + * reclaim just put back on the LRU but has not released yet. + */ pc = lookup_page_cgroup(oldpage); if (!PageCgroupUsed(pc)) return; -- 2.1.2 -- To unsubscribe from this list: send the line "unsubscribe cgroups" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
