Re: [PATCH v4 1/4] mm: fix tracing in free_pcppages_bulk()
From: Andrew Morton <akpm@linux-foundation.org>
Date: 2012-09-19 19:28:02
On Fri, 14 Sep 2012 16:29:31 +0200 Bartlomiej Zolnierkiewicz [off-list ref] 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.
quoted hunk ↗ jump to hunk
--- 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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