From: Johannes Weiner <hannes@xxxxxxxxxxx> Subject: mm: deactivations shouldn't bias the LRU balance Operations like MADV_FREE, FADV_DONTNEED etc. currently move any affected active pages to the inactive list to accelerate their reclaim (good) but also steer page reclaim toward that LRU type, or away from the other (bad). The reason why this is undesirable is that such operations are not part of the regular page aging cycle, and rather a fluke that doesn't say much about the remaining pages on that list; they might all be in heavy use, and once the chunk of easy victims has been purged, the VM continues to apply elevated pressure on those remaining hot pages. The other LRU, meanwhile, might have easily reclaimable pages, and there was never a need to steer away from it in the first place. As the previous patch outlined, we should focus on recording actually observed cost to steer the balance rather than speculating about the potential value of one LRU list over the other. In that spirit, leave explicitely deactivated pages to the LRU algorithm to pick up, and let rotations decide which list is the easiest to reclaim. [cai@xxxxxx: fix set-but-not-used warning] Link: http://lkml.kernel.org/r/20200522133335.GA624@Qians-MacBook-Air.local Link: http://lkml.kernel.org/r/20200520232525.798933-10-hannes@xxxxxxxxxxx Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx> Acked-by: Minchan Kim <minchan@xxxxxxxxxx> Acked-by: Michal Hocko <mhocko@xxxxxxxx> Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> Cc: Rik van Riel <riel@xxxxxxxxxxx> Cc: Qian Cai <cai@xxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/swap.c | 7 +------ 1 file changed, 1 insertion(+), 6 deletions(-) --- a/mm/swap.c~mm-deactivations-shouldnt-bias-the-lru-balance +++ a/mm/swap.c @@ -498,7 +498,7 @@ void lru_cache_add_active_or_unevictable static void lru_deactivate_file_fn(struct page *page, struct lruvec *lruvec, void *arg) { - int lru, file; + int lru; bool active; if (!PageLRU(page)) @@ -512,7 +512,6 @@ static void lru_deactivate_file_fn(struc return; active = PageActive(page); - file = page_is_file_lru(page); lru = page_lru_base_type(page); del_page_from_lru_list(page, lruvec, lru + active); @@ -538,14 +537,12 @@ static void lru_deactivate_file_fn(struc if (active) __count_vm_event(PGDEACTIVATE); - lru_note_cost(lruvec, !file, hpage_nr_pages(page)); } static void lru_deactivate_fn(struct page *page, struct lruvec *lruvec, void *arg) { if (PageLRU(page) && PageActive(page) && !PageUnevictable(page)) { - int file = page_is_file_lru(page); int lru = page_lru_base_type(page); del_page_from_lru_list(page, lruvec, lru + LRU_ACTIVE); @@ -554,7 +551,6 @@ static void lru_deactivate_fn(struct pag add_page_to_lru_list(page, lruvec, lru); __count_vm_events(PGDEACTIVATE, hpage_nr_pages(page)); - lru_note_cost(lruvec, !file, hpage_nr_pages(page)); } } @@ -579,7 +575,6 @@ static void lru_lazyfree_fn(struct page __count_vm_events(PGLAZYFREE, hpage_nr_pages(page)); count_memcg_page_event(page, PGLAZYFREE); - lru_note_cost(lruvec, 0, hpage_nr_pages(page)); } } _
