On Fri 02-11-18 19:38:35, Roman Gushchin wrote:
On Fri, Nov 02, 2018 at 06:48:23PM +0100, Michal Hocko wrote:
On Fri 02-11-18 17:25:58, Roman Gushchin wrote:
On Fri, Nov 02, 2018 at 05:51:47PM +0100, Michal Hocko wrote:
On Fri 02-11-18 16:22:41, Roman Gushchin wrote:
[...]
- We do forget to scan the last page in the LRU list. So if we ended up with
1-page long LRU, it can stay there basically forever.
Why /* * If the cgroup's already been deleted, make sure to * scrape out the remaining cache. */ if (!scan && !mem_cgroup_online(memcg)) scan = min(size, SWAP_CLUSTER_MAX);
in get_scan_count doesn't work for that case?
No, it doesn't. Let's look at the whole picture:
size = lruvec_lru_size(lruvec, lru, sc->reclaim_idx); scan = size >> sc->priority; /* * If the cgroup's already been deleted, make sure to * scrape out the remaining cache. */ if (!scan && !mem_cgroup_online(memcg)) scan = min(size, SWAP_CLUSTER_MAX);
If size == 1, scan == 0 => scan = min(1, 32) == 1. And after proportional adjustment we'll have 0.
My friday brain hurst when looking at this but if it doesn't work as advertized then it should be fixed. I do not see any of your patches to touch this logic so how come it would work after them applied?
This part works as expected. But the following scan = div64_u64(scan * fraction[file], denominator); reliable turns 1 page to scan to 0 pages to scan.
OK, 68600f623d69 ("mm: don't miss the last page because of round-off error") sounds like a good and safe stable backport material.