linux-kernel - Re: [PATCH 1/2] mm, page_isolation: remove bogus tests for isolated pages

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Message-ID: <55AF8BD2.6060009@suse.cz>
Date:	Wed, 22 Jul 2015 14:25:54 +0200
From:	Vlastimil Babka <vbabka@...e.cz>
To:	David Rientjes <rientjes@...gle.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	"minkyung88.kim" <minkyung88.kim@....com>, kmk3210@...il.com,
	Seungho Park <seungho1.park@....com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Minchan Kim <minchan@...nel.org>,
	Michal Nazarewicz <mina86@...a86.com>,
	Laura Abbott <lauraa@...eaurora.org>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Johannes Weiner <hannes@...xchg.org>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Mel Gorman <mgorman@...e.de>
Subject: Re: [PATCH 1/2] mm, page_isolation: remove bogus tests for isolated
 pages

On 07/22/2015 12:43 AM, David Rientjes wrote:
> On Tue, 21 Jul 2015, Vlastimil Babka wrote:
> 
> 
> You may want to consider stating your assumptions explicitly in the code,
> perhaps with VM_BUG_ON(), such as in free_pcppages_bulk() to ensure things
> like get_freepage_migratetype(page) != MIGRATE_ISOLATE.

Hm, OK here's a fixup. I've pondered others but nothing made sense
unless I would have to devise really twisted ways in which somebody
broke the code in the future, and that's not worth BUG_ON().

But the checking made me realize that one more
set_freepage_migratetype() can be removed in the other patch, so I
will resend it.

------8<------
From: Vlastimil Babka <vbabka@...e.cz>
Date: Wed, 22 Jul 2015 14:16:52 +0200
Subject: [PATCH 2/3] fixup! mm, page_isolation: remove bogus tests for
 isolated pages

---
 mm/page_alloc.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 41dc650..c61fef8 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -789,7 +789,11 @@ static void free_pcppages_bulk(struct zone *zone, int count,
 			page = list_entry(list->prev, struct page, lru);
 			/* must delete as __free_one_page list manipulates */
 			list_del(&page->lru);
+
 			mt = get_freepage_migratetype(page);
+			/* MIGRATE_ISOLATE page should not go to pcplists */
+			VM_BUG_ON_PAGE(is_migrate_isolate(mt), page);
+			/* Pageblock could have been isolated meanwhile */
 			if (unlikely(has_isolate_pageblock(zone)))
 				mt = get_pageblock_migratetype(page);
 
-- 
2.4.5


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