linux-kernel - Re: [PATCH] mm: add the block to the tail of the list in expand()

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Date:	Wed, 5 Aug 2015 15:54:26 +0800
From:	Xishi Qiu <qiuxishi@...wei.com>
To:	Dave Hansen <dave.hansen@...el.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>, Vlastimil Babka <vbabka@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...e.cz>, <iamjoonsoo.kim@....com>,
	<alexander.h.duyck@...hat.com>, <sasha.levin@...cle.com>,
	Linux MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm: add the block to the tail of the list in expand()

On 2015/8/4 22:27, Dave Hansen wrote:

> On 08/03/2015 06:13 PM, Xishi Qiu wrote:
>> How did you do the experiment?
> 
> I just stuck in some counters in expand() that looked to see whether the
> list was empty or not when the page is added and then printed them out
> occasionally.
> 

Hi Dave,

I add some debug code like this, but it doesn't trigger the dump_stack().

--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -834,6 +834,12 @@ static inline void expand(struct zone *zone, struct page *page,
                        continue;
                }
 #endif
+
+         if (!list_empty(&area->free_list[migratetype])) {
+                 printk("expand(), the list is not empty\n");
+                 dump_stack();
+         }
+
                list_add(&page[size].lru, &area->free_list[migratetype]);
                area->nr_free++;
                set_page_order(&page[size], high);


> It will be interesting to see the results both on a freshly-booted
> system and one that's reached relatively steady-state and is moving
> around a minimal number of pageblocks between the different types.
> 
> In any case, the end result here needs to be some indication that the
> patch either helps ease fragmentation or helps performance.
> 
> .
> 



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