[RFC] mm: fix a BUG, the page is allocated 2 times

[RFC] mm: fix a BUG, the page is allocated 2 times

[yalin wang]

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

Signed-off-by: yalin wang <yalin.wang2010@gmail.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)
+			page = __rmqueue(zone, order, migratetype, gfp_flags);
 		spin_unlock(&zone->lock);
 		if (!page)
 			goto failed;
-- 
1.9.1

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

[Vlastimil Babka]

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@gmail.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...

> +			page = __rmqueue(zone, order, migratetype, gfp_flags);
>   		spin_unlock(&zone->lock);
>   		if (!page)
>   			goto failed;
>

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

[yalin wang]

> On Oct 12, 2015, at 15:38, Vlastimil Babka <vbabka@suse.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@gmail.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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Re: [RFC] mm: fix a BUG, the page is allocated 2 times

[Kirill A. Shutemov]

On Mon, Oct 12, 2015 at 03:58:51PM +0800, yalin wang wrote:
> 
> > On Oct 12, 2015, at 15:38, Vlastimil Babka <vbabka@suse.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@gmail.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 anywaya?|
> agree with your comments,
> do i need send a new patch for this ?

Looks like a two patches to me: memory leak and removing always-true part
of condifition.

-- 
 Kirill A. Shutemov

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

[Vlastimil Babka]

On 10/12/2015 12:05 PM, Kirill A. Shutemov wrote:
> On Mon, Oct 12, 2015 at 03:58:51PM +0800, yalin wang wrote:
>>
>>> On Oct 12, 2015, at 15:38, Vlastimil Babka <vbabka@suse.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@gmail.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 anywaya?|
>> agree with your comments,
>> do i need send a new patch for this ?

I'd guess no need to, Andrew can edit the patch?

>
> Looks like a two patches to me: memory leak and removing always-true part
> of condifition.

Yeah but I'd expect both would be in the end folded into the buggy patch 
in -mm?

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

[Mel Gorman]

On Mon, Oct 12, 2015 at 10:40:06AM +0800, 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
> 
> Signed-off-by: yalin wang <yalin.wang2010@gmail.com>

Thanks very much for catching this!

Acked-by: Mel Gorman <mgorman@techsingularity.net>

With your current subject and changelog, there is a small risk that Andrew
will miss this or not see it for some time. Would you mind resending the
patch with a changelog similar to this please? It spells out that it is
a fix to an mmotm patch so it'll be obvious where it should be inserted
before merging to mainline.

From: yalin wang <yalin.wang2010@gmail.com>
Subject: [PATCH] mm, page_alloc: reserve pageblocks for high-order atomic allocations on demand -fix

There is a redundant check and a memory leak introduced by a patch in
mmotm. This patch removes an unlikely(order) check as we are sure order
is not zero at the time. It also checks if a page is already allocated
to avoid a memory leak.

This is a fix to the mmotm patch
mm-page_alloc-reserve-pageblocks-for-high-order-atomic-allocations-on-demand.patch

Signed-off-by: yalin wang <yalin.wang2010@gmail.com>
Acked-by: Mel Gorman <mgorman@techsingularity.net>

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

[yalin wang]

> On Oct 12, 2015, at 21:52, Mel Gorman <mgorman@techsingularity.net> wrote:
> 
> There is a redundant check and a memory leak introduced by a patch in
> mmotm. This patch removes an unlikely(order) check as we are sure order
> is not zero at the time. It also checks if a page is already allocated
> to avoid a memory leak.
> 
> This is a fix to the mmotm patch
> mm-page_alloc-reserve-pageblocks-for-high-order-atomic-allocations-on-demand.patch
> 
> Signed-off-by: yalin wang <yalin.wang2010@gmail.com>
> Acked-by: Mel Gorman <mgorman@techsingularity.net>
no problem,
i have send the patch again using your change log .

Thanks
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