From e2b19197ff9dc46f3e3888f273c4395f9e5a9856 Mon Sep 17 00:00:00 2001 From: Mel Gorman Date: Fri, 6 Nov 2015 16:28:09 -0800 Subject: [PATCH] mm, page_alloc: remove unnecessary parameter from zone_watermark_ok_safe Overall, the intent of this series is to remove the zonelist cache which was introduced to avoid high overhead in the page allocator. Once this is done, it is necessary to reduce the cost of watermark checks. The series starts with minor micro-optimisations. Next it notes that GFP flags that affect watermark checks are abused. __GFP_WAIT historically identified callers that could not sleep and could access reserves. This was later abused to identify callers that simply prefer to avoid sleeping and have other options. A patch distinguishes between atomic callers, high-priority callers and those that simply wish to avoid sleep. The zonelist cache has been around for a long time but it is of dubious merit with a lot of complexity and some issues that are explained. The most important issue is that a failed THP allocation can cause a zone to be treated as "full". This potentially causes unnecessary stalls, reclaim activity or remote fallbacks. The issues could be fixed but it's not worth it. The series places a small number of other micro-optimisations on top before examining GFP flags watermarks. High-order watermarks enforcement can cause high-order allocations to fail even though pages are free. The watermark checks both protect high-order atomic allocations and make kswapd aware of high-order pages but there is a much better way that can be handled using migrate types. This series uses page grouping by mobility to reserve pageblocks for high-order allocations with the size of the reservation depending on demand. kswapd awareness is maintained by examining the free lists. By patch 12 in this series, there are no high-order watermark checks while preserving the properties that motivated the introduction of the watermark checks. This patch (of 10): No user of zone_watermark_ok_safe() specifies alloc_flags. This patch removes the unnecessary parameter. Signed-off-by: Mel Gorman Acked-by: David Rientjes Acked-by: Vlastimil Babka Acked-by: Michal Hocko Reviewed-by: Christoph Lameter Acked-by: Johannes Weiner Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/mmzone.h | 2 +- mm/page_alloc.c | 5 +++-- mm/vmscan.c | 4 ++-- 3 files changed, 6 insertions(+), 5 deletions(-) diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h index 2d7e660cdefe..e326843c995a 100644 --- a/include/linux/mmzone.h +++ b/include/linux/mmzone.h @@ -817,7 +817,7 @@ void wakeup_kswapd(struct zone *zone, int order, enum zone_type classzone_idx); bool zone_watermark_ok(struct zone *z, unsigned int order, unsigned long mark, int classzone_idx, int alloc_flags); bool zone_watermark_ok_safe(struct zone *z, unsigned int order, - unsigned long mark, int classzone_idx, int alloc_flags); + unsigned long mark, int classzone_idx); enum memmap_context { MEMMAP_EARLY, MEMMAP_HOTPLUG, diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 446bb36ee59d..d73c346d91b3 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -2249,6 +2249,7 @@ static bool __zone_watermark_ok(struct zone *z, unsigned int order, min -= min / 2; if (alloc_flags & ALLOC_HARDER) min -= min / 4; + #ifdef CONFIG_CMA /* If allocation can't use CMA areas don't use free CMA pages */ if (!(alloc_flags & ALLOC_CMA)) @@ -2278,14 +2279,14 @@ bool zone_watermark_ok(struct zone *z, unsigned int order, unsigned long mark, } bool zone_watermark_ok_safe(struct zone *z, unsigned int order, - unsigned long mark, int classzone_idx, int alloc_flags) + unsigned long mark, int classzone_idx) { long free_pages = zone_page_state(z, NR_FREE_PAGES); if (z->percpu_drift_mark && free_pages < z->percpu_drift_mark) free_pages = zone_page_state_snapshot(z, NR_FREE_PAGES); - return __zone_watermark_ok(z, order, mark, classzone_idx, alloc_flags, + return __zone_watermark_ok(z, order, mark, classzone_idx, 0, free_pages); } diff --git a/mm/vmscan.c b/mm/vmscan.c index 55721b619aee..e0cd7eed4e38 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -2477,7 +2477,7 @@ static inline bool compaction_ready(struct zone *zone, int order) balance_gap = min(low_wmark_pages(zone), DIV_ROUND_UP( zone->managed_pages, KSWAPD_ZONE_BALANCE_GAP_RATIO)); watermark = high_wmark_pages(zone) + balance_gap + (2UL << order); - watermark_ok = zone_watermark_ok_safe(zone, 0, watermark, 0, 0); + watermark_ok = zone_watermark_ok_safe(zone, 0, watermark, 0); /* * If compaction is deferred, reclaim up to a point where @@ -2960,7 +2960,7 @@ static bool zone_balanced(struct zone *zone, int order, unsigned long balance_gap, int classzone_idx) { if (!zone_watermark_ok_safe(zone, order, high_wmark_pages(zone) + - balance_gap, classzone_idx, 0)) + balance_gap, classzone_idx)) return false; if (IS_ENABLED(CONFIG_COMPACTION) && order && compaction_suitable(zone, -- 2.20.1