linux-kernel - Re: [RFC] mm: fix a BUG, the page is allocated 2 times

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Date:	Mon, 12 Oct 2015 15:58:51 +0800
From:	yalin wang <yalin.wang2010@...il.com>
To:	Vlastimil Babka <vbabka@...e.cz>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	mgorman@...hsingularity.net, mhocko@...e.com,
	David Rientjes <rientjes@...gle.com>, js1304@...il.com,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	hannes@...xchg.org, alexander.h.duyck@...hat.com,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC] mm: fix a BUG, the page is allocated 2 times


> On Oct 12, 2015, at 15:38, Vlastimil Babka <vbabka@...e.cz> wrote:
> 
> On 10/12/2015 04:40 AM, yalin wang wrote:
>> Remove unlikely(order), because we are sure order is not zero if
>> code reach here, also add if (page == NULL), only allocate page again if
>> __rmqueue_smallest() failed or alloc_flags & ALLOC_HARDER == 0
> 
> The second mentioned change is actually more important as it removes a memory leak! Thanks for catching this. The problem is in patch mm-page_alloc-reserve-pageblocks-for-high-order-atomic-allocations-on-demand.patch and seems to have been due to a change in the last submitted version to make sure the tracepoint is called.
> 
>> Signed-off-by: yalin wang <yalin.wang2010@...il.com>
>> ---
>>  mm/page_alloc.c | 6 +++---
>>  1 file changed, 3 insertions(+), 3 deletions(-)
>> 
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index 0d6f540..de82e2c 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -2241,13 +2241,13 @@ struct page *buffered_rmqueue(struct zone *preferred_zone,
>>  		spin_lock_irqsave(&zone->lock, flags);
>> 
>>  		page = NULL;
>> -		if (unlikely(order) && (alloc_flags & ALLOC_HARDER)) {
>> +		if (alloc_flags & ALLOC_HARDER) {
>>  			page = __rmqueue_smallest(zone, order, MIGRATE_HIGHATOMIC);
>>  			if (page)
>>  				trace_mm_page_alloc_zone_locked(page, order, migratetype);
>>  		}
>> -
>> -		page = __rmqueue(zone, order, migratetype, gfp_flags);
>> +		if (page == NULL)
> 
> "if (!page)" is more common and already used below.
> We could skip the check for !page in case we don't go through the ALLOC_HARDER branch, but I guess it's not worth the goto, and hopefully the compiler is smart enough anyway…
agree with your comments,
do i need send a new patch for this ?

Thanks

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