From: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> When implementing workingset detection for anonymous page, I found some swapcache pages with NULL memcg. From the code reading, I found two reasons. One is the case that swap-in readahead happens. The other is the corner case related to the shmem cache. These two problems should be fixed, but, it's not straight-forward to fix. For example, when swap-off, all swapped-out pages are read into swapcache. In this case, who's the owner of the swapcache page? Since this problem doesn't look trivial, I decide to leave the issue and handles this corner case on the place where the error occurs. Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> --- mm/workingset.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/mm/workingset.c b/mm/workingset.c index a9f474a..8d2e83a 100644 --- a/mm/workingset.c +++ b/mm/workingset.c @@ -257,6 +257,10 @@ void *workingset_eviction(struct page *page, struct mem_cgroup *target_memcg) VM_BUG_ON_PAGE(page_count(page), page); VM_BUG_ON_PAGE(!PageLocked(page), page); + /* page_memcg() can be NULL if swap-in readahead happens */ + if (!page_memcg(page)) + return NULL; + advance_inactive_age(page_memcg(page), pgdat, is_file); lruvec = mem_cgroup_lruvec(target_memcg, pgdat); -- 2.7.4
