GitLab

commit 71ab6cfe upstream.

get_scan_count() considers the whole node LRU size when

 - doing SCAN_FILE due to many page cache inactive pages
 - calculating the number of pages to scan

In both cases this might lead to unexpected behavior especially on 32b
systems where we can expect lowmem memory pressure very often.

A large highmem zone can easily distort SCAN_FILE heuristic because
there might be only few file pages from the eligible zones on the node
lru and we would still enforce file lru scanning which can lead to
trashing while we could still scan anonymous pages.

The later use of lruvec_lru_size can be problematic as well.  Especially
when there are not many pages from the eligible zones.  We would have to
skip over many pages to find anything to reclaim but shrink_node_memcg
would only reduce the remaining number to scan by SWAP_CLUSTER_MAX at
maximum.  Therefore we can end up going over a large LRU many times
...