Historically when freeing pages, free_one_page() assumed that callers
had IRQs disabled and the zone->lock could be acquired with spin_lock().
This confuses the scope of what local_lock_irq is protecting and what
zone->lock is protecting in free_unref_page_list in particular.
This patch uses spin_lock_irqsave() for the zone->lock in
free_one_page() instead of relying on callers to have disabled
IRQs. free_unref_page_commit() is changed to only deal with PCP pages
protected by the local lock. free_unref_page_list() then first frees
isolated pages to the buddy lists with free_one_page() and frees the rest
of the pages to the PCP via free_unref_page_commit(). The end result
is that free_one_page() is no longer depending on side-effects of
local_lock to be correct.
Note that this may incur a performance penalty while memory hot-remove
is running but that is not a common operation.
Signed-off-by: Mel Gorman <mgor...@techsingularity.net>
---
mm/page_alloc.c | 67 ++++++++++++++++++++++++++++++-------------------
1 file changed, 41 insertions(+), 26 deletions(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 6791e9361076..a0b210077178 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1473,10 +1473,12 @@ static void free_one_page(struct zone *zone,
unsigned int order,
int migratetype, fpi_t fpi_flags)
{
- spin_lock(&zone->lock);
+ unsigned long flags;
+
+ spin_lock_irqsave(&zone->lock, flags);
migratetype = check_migratetype_isolated(zone, page, pfn, migratetype);
__free_one_page(page, pfn, zone, order, migratetype, fpi_flags);
- spin_unlock(&zone->lock);
+ spin_unlock_irqrestore(&zone->lock, flags);
}
static void __meminit __init_single_page(struct page *page, unsigned long pfn,
@@ -3238,31 +3240,13 @@ static bool free_unref_page_prepare(struct page *page,
unsigned long pfn)
return true;
}
-static void free_unref_page_commit(struct page *page, unsigned long pfn)
+static void free_unref_page_commit(struct page *page, unsigned long pfn,
+ int migratetype)
{
struct zone *zone = page_zone(page);
struct per_cpu_pages *pcp;
- int migratetype;
- migratetype = get_pcppage_migratetype(page);
__count_vm_event(PGFREE);
-
- /*
- * We only track unmovable, reclaimable and movable on pcp lists.
- * Free ISOLATE pages back to the allocator because they are being
- * offlined but treat HIGHATOMIC as movable pages so we can get those
- * areas back if necessary. Otherwise, we may have to free
- * excessively into the page allocator
- */
- if (migratetype >= MIGRATE_PCPTYPES) {
- if (unlikely(is_migrate_isolate(migratetype))) {
- free_one_page(zone, page, pfn, 0, migratetype,
- FPI_NONE);
- return;
- }
- migratetype = MIGRATE_MOVABLE;
- }
-
pcp = this_cpu_ptr(zone->per_cpu_pageset);
list_add(&page->lru, &pcp->lists[migratetype]);
pcp->count++;
@@ -3277,12 +3261,29 @@ void free_unref_page(struct page *page)
{
unsigned long flags;
unsigned long pfn = page_to_pfn(page);
+ int migratetype;
if (!free_unref_page_prepare(page, pfn))
return;
+ /*
+ * We only track unmovable, reclaimable and movable on pcp lists.
+ * Place ISOLATE pages on the isolated list because they are being
+ * offlined but treat HIGHATOMIC as movable pages so we can get those
+ * areas back if necessary. Otherwise, we may have to free
+ * excessively into the page allocator
+ */
+ migratetype = get_pcppage_migratetype(page);
+ if (unlikely(migratetype >= MIGRATE_PCPTYPES)) {
+ if (unlikely(is_migrate_isolate(migratetype))) {
+ free_one_page(page_zone(page), page, pfn, 0,
migratetype, FPI_NONE);
+ return;
+ }
+ migratetype = MIGRATE_MOVABLE;
+ }
+
local_lock_irqsave(&pagesets.lock, flags);
- free_unref_page_commit(page, pfn);
+ free_unref_page_commit(page, pfn, migratetype);
local_unlock_irqrestore(&pagesets.lock, flags);
}
@@ -3294,6 +3295,7 @@ void free_unref_page_list(struct list_head *list)
struct page *page, *next;
unsigned long flags, pfn;
int batch_count = 0;
+ int migratetype;
/* Prepare pages for freeing */
list_for_each_entry_safe(page, next, list, lru) {
@@ -3301,15 +3303,28 @@ void free_unref_page_list(struct list_head *list)
if (!free_unref_page_prepare(page, pfn))
list_del(&page->lru);
set_page_private(page, pfn);
+
+ /*
+ * Free isolated pages directly to the allocator, see
+ * comment in free_unref_page.
+ */
+ migratetype = get_pcppage_migratetype(page);
+ if (unlikely(migratetype >= MIGRATE_PCPTYPES)) {
+ if (unlikely(is_migrate_isolate(migratetype))) {
+ free_one_page(page_zone(page), page, pfn, 0,
+ migratetype, FPI_NONE);
+ list_del(&page->lru);
+ }
+ }
}
local_lock_irqsave(&pagesets.lock, flags);
list_for_each_entry_safe(page, next, list, lru) {
- unsigned long pfn = page_private(page);
-
+ pfn = page_private(page);
set_page_private(page, 0);
+ migratetype = get_pcppage_migratetype(page);
trace_mm_page_free_batched(page);
- free_unref_page_commit(page, pfn);
+ free_unref_page_commit(page, pfn, migratetype);
/*
* Guard against excessive IRQ disabled times when we get
--
2.26.2
