From: Minchan Kim Date: Tue, 26 Oct 2010 21:21:31 +0000 (-0700) Subject: vmscan: prevent background aging of anon page in no swap system X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=74e3f3c3391d81a959f58a1191a560703a4415b4;p=GitHub%2FLineageOS%2Fandroid_kernel_motorola_exynos9610.git vmscan: prevent background aging of anon page in no swap system Ying Han reported that backing aging of anon pages in no swap system causes unnecessary TLB flush. When I sent a patch(69c8548175), I wanted this patch but Rik pointed out and allowed aging of anon pages to give a chance to promote from inactive to active LRU. It has a two problem. 1) non-swap system Never make sense to age anon pages. 2) swap configured but still doesn't swapon It doesn't make sense to age anon pages until swap-on time. But it's arguable. If we have aged anon pages by swapon, VM have moved anon pages from active to inactive. And in the time swapon by admin, the VM can't reclaim hot pages so we can protect hot pages swapout. But let's think about it. When does swap-on happen? It depends on admin. we can't expect it. Nonetheless, we have done aging of anon pages to protect hot pages swapout. It means we lost run time overhead when below high watermark but gain hot page swap-[in/out] overhead when VM decide swapout. Is it true? Let's think more detail. We don't promote anon pages in case of non-swap system. So even though VM does aging of anon pages, the pages would be in inactive LRU for a long time. It means many of pages in there would mark access bit again. So access bit hot/code separation would be pointless. This patch prevents unnecessary anon pages demotion in not-yet-swapon and non-configured swap system. Even, in non-configuared swap system inactive_anon_is_low can be compiled out. It could make side effect that hot anon pages could swap out when admin does swap on. But I think sooner or later it would be steady state. So it's not a big problem. We could lose someting but gain more thing(TLB flush and unnecessary function call to demote anon pages). Signed-off-by: Ying Han Signed-off-by: Minchan Kim Reviewed-by: Rik van Riel Reviewed-by: KOSAKI Motohiro Cc: Johannes Weiner Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/mm/vmscan.c b/mm/vmscan.c index f5871ee50000..0c33a0997907 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -1505,6 +1505,7 @@ static void shrink_active_list(unsigned long nr_pages, struct zone *zone, spin_unlock_irq(&zone->lru_lock); } +#ifdef CONFIG_SWAP static int inactive_anon_is_low_global(struct zone *zone) { unsigned long active, inactive; @@ -1530,12 +1531,26 @@ static int inactive_anon_is_low(struct zone *zone, struct scan_control *sc) { int low; + /* + * If we don't have swap space, anonymous page deactivation + * is pointless. + */ + if (!total_swap_pages) + return 0; + if (scanning_global_lru(sc)) low = inactive_anon_is_low_global(zone); else low = mem_cgroup_inactive_anon_is_low(sc->mem_cgroup); return low; } +#else +static inline int inactive_anon_is_low(struct zone *zone, + struct scan_control *sc) +{ + return 0; +} +#endif static int inactive_file_is_low_global(struct zone *zone) { @@ -1781,7 +1796,7 @@ static void shrink_zone(int priority, struct zone *zone, * Even if we did not try to evict anon pages at all, we want to * rebalance the anon lru active/inactive ratio. */ - if (inactive_anon_is_low(zone, sc) && nr_swap_pages > 0) + if (inactive_anon_is_low(zone, sc)) shrink_active_list(SWAP_CLUSTER_MAX, zone, sc, priority, 0); throttle_vm_writeout(sc->gfp_mask);