On Fri, 14 Sep 2012 16:29:31 +0200
Bartlomiej Zolnierkiewicz <b.zolnierkie@xxxxxxxxxxx> wrote:
> page->private gets re-used in __free_one_page() to store page order
> (so trace_mm_page_pcpu_drain() may print order instead of migratetype)
> thus migratetype value must be cached locally.
>
> Fixes regression introduced in a701623 ("mm: fix migratetype bug
> which slowed swapping").
Grumble. Please describe a bug when fixing it! I've added here the
text "This caused incorrect data to be attached to the
mm_page_pcpu_drain trace event", which is hopefully correct enough.
As it's been this way for 2.5 years, I assume that this can wait for
3.7.
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -668,12 +668,15 @@ static void free_pcppages_bulk(struct zone *zone, int count,
> batch_free = to_free;
>
> do {
> + int mt;
> +
> page = list_entry(list->prev, struct page, lru);
> /* must delete as __free_one_page list manipulates */
> list_del(&page->lru);
> + mt = page_private(page);
> /* MIGRATE_MOVABLE list may include MIGRATE_RESERVEs */
> - __free_one_page(page, zone, 0, page_private(page));
> - trace_mm_page_pcpu_drain(page, 0, page_private(page));
> + __free_one_page(page, zone, 0, mt);
> + trace_mm_page_pcpu_drain(page, 0, mt);
> } while (--to_free && --batch_free && !list_empty(list));
> }
> __mod_zone_page_state(zone, NR_FREE_PAGES, count);
More grumble. Look:
akpm:/usr/src/25> grep migratetype mm/page_alloc.c | wc -l
115
We should respect the established naming conventions. But reusing
local var `maigratetype' here is not good practice, so how about
--- a/mm/page_alloc.c~mm-fix-tracing-in-free_pcppages_bulk-fix
+++ a/mm/page_alloc.c
@@ -668,7 +668,7 @@ static void free_pcppages_bulk(struct zo
batch_free = to_free;
do {
- int mt;
+ int mt; /* migratetype of the to-be-freed page */
page = list_entry(list->prev, struct page, lru);
/* must delete as __free_one_page list manipulates */
_
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