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

From: Vlastimil Babka
Date: Fri Jan 20 2017 - 10:03:05 EST


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]);