From: Johannes Weiner <hannes@xxxxxxxxxxx> Subject: mm: vmscan: move dirty pages out of the way until they're flushed We noticed a performance regression when moving hadoop workloads from 3.10 kernels to 4.0 and 4.6. This is accompanied by increased pageout activity initiated by kswapd as well as frequent bursts of allocation stalls and direct reclaim scans. Even lowering the dirty ratios to the equivalent of less than 1% of memory would not eliminate the issue, suggesting that dirty pages concentrate where the scanner is looking. This can be traced back to recent efforts of thrash avoidance. Where 3.10 would not detect refaulting pages and continuously supply clean cache to the inactive list, a thrashing workload on 4.0+ will detect and activate refaulting pages right away, distilling used-once pages on the inactive list much more effectively. This is by design, and it makes sense for clean cache. But for the most part our workload's cache faults are refaults and its use-once cache is from streaming writes. We end up with most of the inactive list dirty, and we don't go after the active cache as long as we have use-once pages around. But waiting for writes to avoid reclaiming clean cache that *might* refault is a bad trade-off. Even if the refaults happen, reads are faster than writes. Before getting bogged down on writeback, reclaim should first look at *all* cache in the system, even active cache. To accomplish this, activate pages that are dirty or under writeback when they reach the end of the inactive LRU. The pages are marked for immediate reclaim, meaning they'll get moved back to the inactive LRU tail as soon as they're written back and become reclaimable. But in the meantime, by reducing the inactive list to only immediately reclaimable pages, we allow the scanner to deactivate and refill the inactive list with clean cache from the active list tail to guarantee forward progress. [hannes@xxxxxxxxxxx: update comment] Link: http://lkml.kernel.org/r/20170202191957.22872-8-hannes@xxxxxxxxxxx Link: http://lkml.kernel.org/r/20170123181641.23938-6-hannes@xxxxxxxxxxx Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx> Acked-by: Minchan Kim <minchan@xxxxxxxxxx> Acked-by: Michal Hocko <mhocko@xxxxxxxx> Acked-by: Hillf Danton <hillf.zj@xxxxxxxxxxxxxxx> Cc: Mel Gorman <mgorman@xxxxxxx> Cc: Rik van Riel <riel@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- include/linux/mm_inline.h | 7 +++++++ mm/swap.c | 9 +++++---- mm/vmscan.c | 15 ++++++++++++--- 3 files changed, 24 insertions(+), 7 deletions(-) diff -puN include/linux/mm_inline.h~mm-vmscan-move-dirty-pages-out-of-the-way-until-theyre-flushed include/linux/mm_inline.h --- a/include/linux/mm_inline.h~mm-vmscan-move-dirty-pages-out-of-the-way-until-theyre-flushed +++ a/include/linux/mm_inline.h @@ -50,6 +50,13 @@ static __always_inline void add_page_to_ list_add(&page->lru, &lruvec->lists[lru]); } +static __always_inline void add_page_to_lru_list_tail(struct page *page, + struct lruvec *lruvec, enum lru_list lru) +{ + update_lru_size(lruvec, lru, page_zonenum(page), hpage_nr_pages(page)); + list_add_tail(&page->lru, &lruvec->lists[lru]); +} + static __always_inline void del_page_from_lru_list(struct page *page, struct lruvec *lruvec, enum lru_list lru) { diff -puN mm/swap.c~mm-vmscan-move-dirty-pages-out-of-the-way-until-theyre-flushed mm/swap.c --- a/mm/swap.c~mm-vmscan-move-dirty-pages-out-of-the-way-until-theyre-flushed +++ a/mm/swap.c @@ -209,9 +209,10 @@ static void pagevec_move_tail_fn(struct { int *pgmoved = arg; - if (PageLRU(page) && !PageActive(page) && !PageUnevictable(page)) { - enum lru_list lru = page_lru_base_type(page); - list_move_tail(&page->lru, &lruvec->lists[lru]); + if (PageLRU(page) && !PageUnevictable(page)) { + del_page_from_lru_list(page, lruvec, page_lru(page)); + ClearPageActive(page); + add_page_to_lru_list_tail(page, lruvec, page_lru(page)); (*pgmoved)++; } } @@ -235,7 +236,7 @@ static void pagevec_move_tail(struct pag */ void rotate_reclaimable_page(struct page *page) { - if (!PageLocked(page) && !PageDirty(page) && !PageActive(page) && + if (!PageLocked(page) && !PageDirty(page) && !PageUnevictable(page) && PageLRU(page)) { struct pagevec *pvec; unsigned long flags; diff -puN mm/vmscan.c~mm-vmscan-move-dirty-pages-out-of-the-way-until-theyre-flushed mm/vmscan.c --- a/mm/vmscan.c~mm-vmscan-move-dirty-pages-out-of-the-way-until-theyre-flushed +++ a/mm/vmscan.c @@ -1056,6 +1056,15 @@ static unsigned long shrink_page_list(st * throttling so we could easily OOM just because too many * pages are in writeback and there is nothing else to * reclaim. Wait for the writeback to complete. + * + * In cases 1) and 2) we activate the pages to get them out of + * the way while we continue scanning for clean pages on the + * inactive list and refilling from the active list. The + * observation here is that waiting for disk writes is more + * expensive than potentially causing reloads down the line. + * Since they're marked for immediate reclaim, they won't put + * memory pressure on the cache working set any longer than it + * takes to write them to disk. */ if (PageWriteback(page)) { /* Case 1 above */ @@ -1063,7 +1072,7 @@ static unsigned long shrink_page_list(st PageReclaim(page) && test_bit(PGDAT_WRITEBACK, &pgdat->flags)) { nr_immediate++; - goto keep_locked; + goto activate_locked; /* Case 2 above */ } else if (sane_reclaim(sc) || @@ -1081,7 +1090,7 @@ static unsigned long shrink_page_list(st */ SetPageReclaim(page); nr_writeback++; - goto keep_locked; + goto activate_locked; /* Case 3 above */ } else { @@ -1174,7 +1183,7 @@ static unsigned long shrink_page_list(st inc_node_page_state(page, NR_VMSCAN_IMMEDIATE); SetPageReclaim(page); - goto keep_locked; + goto activate_locked; } if (references == PAGEREF_RECLAIM_CLEAN) _ -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
