On Wed, Jul 20, 2016 at 04:21:47PM +0100, Mel Gorman wrote:
> Page reclaim determines whether a pgdat is unreclaimable by examining how
> many pages have been scanned since a page was freed and comparing that
> to the LRU sizes. Skipped pages are not considered reclaim candidates but
> contribute to scanned. This can prematurely mark a pgdat as unreclaimable
> and trigger an OOM kill.
>
> While this does not fix an OOM kill message reported by Joonsoo Kim,
> it did stop pgdat being marked unreclaimable.
>
> Signed-off-by: Mel Gorman <mgor...@techsingularity.net>
> ---
> mm/vmscan.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 22aec2bcfeec..b16d578ce556 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1415,7 +1415,7 @@ static unsigned long isolate_lru_pages(unsigned long
> nr_to_scan,
> LIST_HEAD(pages_skipped);
>
> for (scan = 0; scan < nr_to_scan && nr_taken < nr_to_scan &&
> - !list_empty(src); scan++) {
> + !list_empty(src);) {
> struct page *page;
>
> page = lru_to_page(src);
> @@ -1429,6 +1429,9 @@ static unsigned long isolate_lru_pages(unsigned long
> nr_to_scan,
> continue;
> }
>
> + /* Pages skipped do not contribute to scan */
The comment should explain why.
/* Pages skipped do not contribute to scan to prevent premature OOM */
> + scan++;
> +
The one of my concern about node-lru is to add more lru lock contetion
in multiple zone system so such unbounded skip scanning under the lock
should have a limit to prevent latency spike and serialization of
current reclaim work.
Another concern is big mismatch between the number of pages from list and
LRU stat count because lruvec_lru_size call sites don't take the stat
under the lock while isolate_lru_pages moves many pages from lru list
to temporal skipped list.
> switch (__isolate_lru_page(page, mode)) {
> case 0:
> nr_pages = hpage_nr_pages(page);
> --
> 2.6.4
>
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