Re: [PATCH 4/4] mm, page_alloc: Only use per-cpu allocator for irq-safe requests

[Vlastimil Babka]

On 01/17/2017 10:29 AM, Mel Gorman wrote:

[...]

> @@ -1244,10 +1243,8 @@ static void __free_pages_ok(struct page *page, 
> unsigned int order)
>               return;
>  
>       migratetype = get_pfnblock_migratetype(page, pfn);
> -     local_irq_save(flags);
> -     __count_vm_events(PGFREE, 1 << order);
> +     count_vm_events(PGFREE, 1 << order);

Maybe this could be avoided by moving the counting into free_one_page()?
Diff suggestion at the end of e-mail.

>       free_one_page(page_zone(page), page, pfn, order, migratetype);
> -     local_irq_restore(flags);
>  }
>  
>  static void __init __free_pages_boot_core(struct page *page, unsigned int 
> order)
> @@ -2219,8 +2216,9 @@ static int rmqueue_bulk(struct zone *zone, unsigned int 
> order,
>                       int migratetype, bool cold)
>  {
>       int i, alloced = 0;
> +     unsigned long flags;
>  
> -     spin_lock(&zone->lock);
> +     spin_lock_irqsave(&zone->lock, flags);
>       for (i = 0; i < count; ++i) {
>               struct page *page = __rmqueue(zone, order, migratetype);
>               if (unlikely(page == NULL))
> @@ -2256,7 +2254,7 @@ static int rmqueue_bulk(struct zone *zone, unsigned int 
> order,
>        * pages added to the pcp list.
>        */
>       __mod_zone_page_state(zone, NR_FREE_PAGES, -(i << order));
> -     spin_unlock(&zone->lock);
> +     spin_unlock_irqrestore(&zone->lock, flags);
>       return alloced;
>  }
>  
> @@ -2472,16 +2470,20 @@ void free_hot_cold_page(struct page *page, bool cold)
>  {
>       struct zone *zone = page_zone(page);
>       struct per_cpu_pages *pcp;
> -     unsigned long flags;
>       unsigned long pfn = page_to_pfn(page);
>       int migratetype;
>  
>       if (!free_pcp_prepare(page))
>               return;
>  
> +     if (in_interrupt()) {
> +             __free_pages_ok(page, 0);
> +             return;
> +     }

I think this should go *before* free_pcp_prepare() otherwise
free_pages_prepare() gets done twice in interrupt.


diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 15b11fc0cd75..8c6f8a790272 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1149,6 +1149,7 @@ static void free_one_page(struct zone *zone,
 {
        unsigned long nr_scanned, flags;
        spin_lock_irqsave(&zone->lock, flags);
+       __count_vm_events(PGFREE, 1 << order);
        nr_scanned = node_page_state(zone->zone_pgdat, NR_PAGES_SCANNED);
        if (nr_scanned)
                __mod_node_page_state(zone->zone_pgdat, NR_PAGES_SCANNED, 
-nr_scanned);
@@ -1243,7 +1244,6 @@ static void __free_pages_ok(struct page *page, unsigned 
int order)
                return;
 
        migratetype = get_pfnblock_migratetype(page, pfn);
-       count_vm_events(PGFREE, 1 << order);
        free_one_page(page_zone(page), page, pfn, order, migratetype);
 }
 
@@ -2484,7 +2484,6 @@ void free_hot_cold_page(struct page *page, bool cold)
        migratetype = get_pfnblock_migratetype(page, pfn);
        set_pcppage_migratetype(page, migratetype);
        preempt_disable();
-       __count_vm_event(PGFREE);
 
        /*
         * We only track unmovable, reclaimable and movable on pcp lists.
@@ -2501,6 +2500,7 @@ void free_hot_cold_page(struct page *page, bool cold)
                migratetype = MIGRATE_MOVABLE;
        }
 
+       __count_vm_event(PGFREE);
        pcp = &this_cpu_ptr(zone->pageset)->pcp;
        if (!cold)
                list_add(&page->lru, &pcp->lists[migratetype]);