Re: [RFC] mm: bail out in shrin_inactive_list
From: Mel Gorman <mgorman@suse.de>
Date: 2016-07-25 09:29:19
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lkml
There is a typo in the subject line. On Mon, Jul 25, 2016 at 04:51:59PM +0900, Minchan Kim wrote:
With node-lru, if there are enough reclaimable pages in highmem but nothing in lowmem, VM can try to shrink inactive list although the requested zone is lowmem. The problem is direct reclaimer scans inactive list is fulled with
highmem pages to find a victim page at a reqested zone or lower zones but the result is that VM should skip all of pages.
Rephease -- The problem is that if the inactive list is full of highmem pages then a direct reclaimer searching for a lowmem page waste CPU scanning uselessly.
CPU. Even, many direct reclaimers are stalled by too_many_isolated if lots of parallel reclaimer are going on although there are no reclaimable memory in inactive list. I tried the experiment 4 times in 32bit 2G 8 CPU KVM machine to get elapsed time. hackbench 500 process 2 = Old = 1st: 289s 2nd: 310s 3rd: 112s 4th: 272s = Now = 1st: 31s 2nd: 132s 3rd: 162s 4th: 50s. Signed-off-by: Minchan Kim <minchan@kernel.org> --- I believe proper fix is to modify get_scan_count. IOW, I think we should introduce lruvec_reclaimable_lru_size with proper classzone_idx but I don't know how we can fix it with memcg which doesn't have zone stat now. should introduce zone stat back to memcg? Or, it's okay to ignore memcg?
I think it's ok to ignore memcg in this case as a memcg shrink is often going to be for pages that can use highmem anyway.
quoted hunk ↗ jump to hunk
mm/vmscan.c | 28 ++++++++++++++++++++++++++++ 1 file changed, 28 insertions(+)diff --git a/mm/vmscan.c b/mm/vmscan.c index e5af357..3d285cc 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c@@ -1652,6 +1652,31 @@ static int current_may_throttle(void) bdi_write_congested(current->backing_dev_info); } +static inline bool inactive_reclaimable_pages(struct lruvec *lruvec, + struct scan_control *sc, + enum lru_list lru)
inline is unnecessary. The function is long but only has one caller so it'll be inlined automatically.
+{
+ int zid;
+ struct zone *zone;
+ bool file = is_file_lru(lru);It's more appropriate to use int for file in this case as it's used as a multiplier. It'll work either way. Otherwise; Acked-by: Mel Gorman <redacted> -- Mel Gorman SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>