[patch] mm: compaction: make compact_control order signed

[patch] mm: compaction: make compact_control order signed

[Dan Carpenter]

"order" is -1 when compacting via /proc/sys/vm/compact_memory.  Making
it unsigned causes a bug in __compact_pgdat() when we test:

	if (cc->order < 0 || !compaction_deferred(zone, cc->order))
		compact_zone(zone, cc);

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>

diff --git a/mm/compaction.c b/mm/compaction.c
index 382831e..5f80a11 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -35,7 +35,7 @@ struct compact_control {
 	unsigned long migrate_pfn;	/* isolate_migratepages search base */
 	bool sync;			/* Synchronous migration */
 
-	unsigned int order;		/* order a direct compactor needs */
+	int order;			/* order a direct compactor needs */
 	int migratetype;		/* MOVABLE, RECLAIMABLE etc */
 	struct zone *zone;
 };

[patch] mm: compaction: make compact_control order signed

[Dan Carpenter]

"order" is -1 when compacting via /proc/sys/vm/compact_memory.  Making
it unsigned causes a bug in __compact_pgdat() when we test:

	if (cc->order < 0 || !compaction_deferred(zone, cc->order))
		compact_zone(zone, cc);

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>

diff --git a/mm/compaction.c b/mm/compaction.c
index 382831e..5f80a11 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -35,7 +35,7 @@ struct compact_control {
 	unsigned long migrate_pfn;	/* isolate_migratepages search base */
 	bool sync;			/* Synchronous migration */
 
-	unsigned int order;		/* order a direct compactor needs */
+	int order;			/* order a direct compactor needs */
 	int migratetype;		/* MOVABLE, RECLAIMABLE etc */
 	struct zone *zone;
 };

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Re: [patch] mm: compaction: make compact_control order signed

[Rik van Riel]

On 02/01/2012 09:41 AM, Dan Carpenter wrote:
> "order" is -1 when compacting via /proc/sys/vm/compact_memory.  Making
> it unsigned causes a bug in __compact_pgdat() when we test:
>
> 	if (cc->order<  0 || !compaction_deferred(zone, cc->order))
> 		compact_zone(zone, cc);

Good catch!  I had not even thought to check whether
order was signed in struct compact_control, when I
saw code using -1 as an order in various places :)

> Signed-off-by: Dan Carpenter<dan.carpenter@oracle.com>

Reviewed-by: Rik van Riel <riel@redhat.com>

-- 
All rights reversed

Re: [patch] mm: compaction: make compact_control order signed

[Rik van Riel]

On 02/01/2012 09:41 AM, Dan Carpenter wrote:
> "order" is -1 when compacting via /proc/sys/vm/compact_memory.  Making
> it unsigned causes a bug in __compact_pgdat() when we test:
>
> 	if (cc->order<  0 || !compaction_deferred(zone, cc->order))
> 		compact_zone(zone, cc);

Good catch!  I had not even thought to check whether
order was signed in struct compact_control, when I
saw code using -1 as an order in various places :)

> Signed-off-by: Dan Carpenter<dan.carpenter@oracle.com>

Reviewed-by: Rik van Riel <riel@redhat.com>

-- 
All rights reversed

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Re: [patch] mm: compaction: make compact_control order signed

[Andrew Morton]

On Wed, 1 Feb 2012 17:41:01 +0300
Dan Carpenter <dan.carpenter@oracle.com> wrote:

> "order" is -1 when compacting via /proc/sys/vm/compact_memory.  Making
> it unsigned causes a bug in __compact_pgdat() when we test:
> 
> 	if (cc->order < 0 || !compaction_deferred(zone, cc->order))
> 		compact_zone(zone, cc);
> 
> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> 
> diff --git a/mm/compaction.c b/mm/compaction.c
> index 382831e..5f80a11 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -35,7 +35,7 @@ struct compact_control {
>  	unsigned long migrate_pfn;	/* isolate_migratepages search base */
>  	bool sync;			/* Synchronous migration */
>  
> -	unsigned int order;		/* order a direct compactor needs */
> +	int order;			/* order a direct compactor needs */
>  	int migratetype;		/* MOVABLE, RECLAIMABLE etc */
>  	struct zone *zone;
>  };

One would expect this to significantly change the behaviour of
/proc/sys/vm/compact_memory.  Enfeebled minds want to know: is
the new behaviour better or worse than the old behaviour?

Re: [patch] mm: compaction: make compact_control order signed

[Andrew Morton]

On Wed, 1 Feb 2012 17:41:01 +0300
Dan Carpenter <dan.carpenter@oracle.com> wrote:

> "order" is -1 when compacting via /proc/sys/vm/compact_memory.  Making
> it unsigned causes a bug in __compact_pgdat() when we test:
> 
> 	if (cc->order < 0 || !compaction_deferred(zone, cc->order))
> 		compact_zone(zone, cc);
> 
> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> 
> diff --git a/mm/compaction.c b/mm/compaction.c
> index 382831e..5f80a11 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -35,7 +35,7 @@ struct compact_control {
>  	unsigned long migrate_pfn;	/* isolate_migratepages search base */
>  	bool sync;			/* Synchronous migration */
>  
> -	unsigned int order;		/* order a direct compactor needs */
> +	int order;			/* order a direct compactor needs */
>  	int migratetype;		/* MOVABLE, RECLAIMABLE etc */
>  	struct zone *zone;
>  };

One would expect this to significantly change the behaviour of
/proc/sys/vm/compact_memory.  Enfeebled minds want to know: is
the new behaviour better or worse than the old behaviour?

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Re: [patch] mm: compaction: make compact_control order signed

[Rik van Riel]

On 02/01/2012 03:46 PM, Andrew Morton wrote:
> On Wed, 1 Feb 2012 17:41:01 +0300
> Dan Carpenter<dan.carpenter@oracle.com>  wrote:
>
>> "order" is -1 when compacting via /proc/sys/vm/compact_memory.  Making
>> it unsigned causes a bug in __compact_pgdat() when we test:
>>
>> 	if (cc->order<  0 || !compaction_deferred(zone, cc->order))
>> 		compact_zone(zone, cc);
>>
>> Signed-off-by: Dan Carpenter<dan.carpenter@oracle.com>
>>
>> diff --git a/mm/compaction.c b/mm/compaction.c
>> index 382831e..5f80a11 100644
>> --- a/mm/compaction.c
>> +++ b/mm/compaction.c
>> @@ -35,7 +35,7 @@ struct compact_control {
>>   	unsigned long migrate_pfn;	/* isolate_migratepages search base */
>>   	bool sync;			/* Synchronous migration */
>>
>> -	unsigned int order;		/* order a direct compactor needs */
>> +	int order;			/* order a direct compactor needs */
>>   	int migratetype;		/* MOVABLE, RECLAIMABLE etc */
>>   	struct zone *zone;
>>   };
>
> One would expect this to significantly change the behaviour of
> /proc/sys/vm/compact_memory.  Enfeebled minds want to know: is
> the new behaviour better or worse than the old behaviour?

The old behaviour and the behaviour post Dan's fix are the
same.

My patch temporarily broke things, by testing for order < 0,
instead of the explicit cc->order = -1 used elsewhere in
the code.

I did not notice it in my own testing because I tested on
3.2.0 and sent you patches against 3.3-current. It looks
like this line of code is the one difference between both
trees I was working on :(

In my test tree, I had (cc->sync || !compaction_deferred(zone, cc->order)).

Arguably, testing for cc->order = -1 (or cc->order < 0) is
better anyway.

-- 
All rights reversed

Re: [patch] mm: compaction: make compact_control order signed

[Rik van Riel]

On 02/01/2012 03:46 PM, Andrew Morton wrote:
> On Wed, 1 Feb 2012 17:41:01 +0300
> Dan Carpenter<dan.carpenter@oracle.com>  wrote:
>
>> "order" is -1 when compacting via /proc/sys/vm/compact_memory.  Making
>> it unsigned causes a bug in __compact_pgdat() when we test:
>>
>> 	if (cc->order<  0 || !compaction_deferred(zone, cc->order))
>> 		compact_zone(zone, cc);
>>
>> Signed-off-by: Dan Carpenter<dan.carpenter@oracle.com>
>>
>> diff --git a/mm/compaction.c b/mm/compaction.c
>> index 382831e..5f80a11 100644
>> --- a/mm/compaction.c
>> +++ b/mm/compaction.c
>> @@ -35,7 +35,7 @@ struct compact_control {
>>   	unsigned long migrate_pfn;	/* isolate_migratepages search base */
>>   	bool sync;			/* Synchronous migration */
>>
>> -	unsigned int order;		/* order a direct compactor needs */
>> +	int order;			/* order a direct compactor needs */
>>   	int migratetype;		/* MOVABLE, RECLAIMABLE etc */
>>   	struct zone *zone;
>>   };
>
> One would expect this to significantly change the behaviour of
> /proc/sys/vm/compact_memory.  Enfeebled minds want to know: is
> the new behaviour better or worse than the old behaviour?

The old behaviour and the behaviour post Dan's fix are the
same.

My patch temporarily broke things, by testing for order < 0,
instead of the explicit cc->order == -1 used elsewhere in
the code.

I did not notice it in my own testing because I tested on
3.2.0 and sent you patches against 3.3-current. It looks
like this line of code is the one difference between both
trees I was working on :(

In my test tree, I had (cc->sync || !compaction_deferred(zone, cc->order)).

Arguably, testing for cc->order == -1 (or cc->order < 0) is
better anyway.

-- 
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Re: [patch] mm: compaction: make compact_control order signed

[Andrew Morton]

On Wed, 01 Feb 2012 16:17:10 -0500
Rik van Riel <riel@redhat.com> wrote:

> >> @@ -35,7 +35,7 @@ struct compact_control {
> >>   	unsigned long migrate_pfn;	/* isolate_migratepages search base */
> >>   	bool sync;			/* Synchronous migration */
> >>
> >> -	unsigned int order;		/* order a direct compactor needs */
> >> +	int order;			/* order a direct compactor needs */
> >>   	int migratetype;		/* MOVABLE, RECLAIMABLE etc */
> >>   	struct zone *zone;
> >>   };
> >
> > One would expect this to significantly change the behaviour of
> > /proc/sys/vm/compact_memory.  Enfeebled minds want to know: is
> > the new behaviour better or worse than the old behaviour?
> 
> The old behaviour and the behaviour post Dan's fix are the
> same.
> 
> My patch temporarily broke things, by testing for order < 0,
> instead of the explicit cc->order = -1 used elsewhere in
> the code.
> 
> I did not notice it in my own testing because I tested on
> 3.2.0 and sent you patches against 3.3-current. It looks
> like this line of code is the one difference between both
> trees I was working on :(
> 
> In my test tree, I had (cc->sync || !compaction_deferred(zone, cc->order)).
> 
> Arguably, testing for cc->order = -1 (or cc->order < 0) is
> better anyway.

I suppose it would be nicer to make the code in __compact_pgdat() match
all the other places whcih do this:

--- a/mm/compaction.c~mm-compaction-make-compact_control-order-signed-fix
+++ a/mm/compaction.c
@@ -686,7 +686,7 @@ static int __compact_pgdat(pg_data_t *pg
 		INIT_LIST_HEAD(&cc->freepages);
 		INIT_LIST_HEAD(&cc->migratepages);
 
-		if (cc->order < 0 || !compaction_deferred(zone, cc->order))
+		if (cc->order = -1 || !compaction_deferred(zone, cc->order))
 			compact_zone(zone, cc);
 
 		if (cc->order > 0) {
_

Re: [patch] mm: compaction: make compact_control order signed

[Andrew Morton]

On Wed, 01 Feb 2012 16:17:10 -0500
Rik van Riel <riel@redhat.com> wrote:

> >> @@ -35,7 +35,7 @@ struct compact_control {
> >>   	unsigned long migrate_pfn;	/* isolate_migratepages search base */
> >>   	bool sync;			/* Synchronous migration */
> >>
> >> -	unsigned int order;		/* order a direct compactor needs */
> >> +	int order;			/* order a direct compactor needs */
> >>   	int migratetype;		/* MOVABLE, RECLAIMABLE etc */
> >>   	struct zone *zone;
> >>   };
> >
> > One would expect this to significantly change the behaviour of
> > /proc/sys/vm/compact_memory.  Enfeebled minds want to know: is
> > the new behaviour better or worse than the old behaviour?
> 
> The old behaviour and the behaviour post Dan's fix are the
> same.
> 
> My patch temporarily broke things, by testing for order < 0,
> instead of the explicit cc->order == -1 used elsewhere in
> the code.
> 
> I did not notice it in my own testing because I tested on
> 3.2.0 and sent you patches against 3.3-current. It looks
> like this line of code is the one difference between both
> trees I was working on :(
> 
> In my test tree, I had (cc->sync || !compaction_deferred(zone, cc->order)).
> 
> Arguably, testing for cc->order == -1 (or cc->order < 0) is
> better anyway.

I suppose it would be nicer to make the code in __compact_pgdat() match
all the other places whcih do this:

--- a/mm/compaction.c~mm-compaction-make-compact_control-order-signed-fix
+++ a/mm/compaction.c
@@ -686,7 +686,7 @@ static int __compact_pgdat(pg_data_t *pg
 		INIT_LIST_HEAD(&cc->freepages);
 		INIT_LIST_HEAD(&cc->migratepages);
 
-		if (cc->order < 0 || !compaction_deferred(zone, cc->order))
+		if (cc->order == -1 || !compaction_deferred(zone, cc->order))
 			compact_zone(zone, cc);
 
 		if (cc->order > 0) {
_

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Re: [patch] mm: compaction: make compact_control order signed

[Rik van Riel]

On 02/01/2012 04:24 PM, Andrew Morton wrote:
> On Wed, 01 Feb 2012 16:17:10 -0500
> Rik van Riel<riel@redhat.com>  wrote:
>
>>>> @@ -35,7 +35,7 @@ struct compact_control {
>>>>    	unsigned long migrate_pfn;	/* isolate_migratepages search base */
>>>>    	bool sync;			/* Synchronous migration */
>>>>
>>>> -	unsigned int order;		/* order a direct compactor needs */
>>>> +	int order;			/* order a direct compactor needs */
>>>>    	int migratetype;		/* MOVABLE, RECLAIMABLE etc */
>>>>    	struct zone *zone;
>>>>    };
>>>
>>> One would expect this to significantly change the behaviour of
>>> /proc/sys/vm/compact_memory.  Enfeebled minds want to know: is
>>> the new behaviour better or worse than the old behaviour?
>>
>> The old behaviour and the behaviour post Dan's fix are the
>> same.
>>
>> My patch temporarily broke things, by testing for order<  0,
>> instead of the explicit cc->order = -1 used elsewhere in
>> the code.
>>
>> I did not notice it in my own testing because I tested on
>> 3.2.0 and sent you patches against 3.3-current. It looks
>> like this line of code is the one difference between both
>> trees I was working on :(
>>
>> In my test tree, I had (cc->sync || !compaction_deferred(zone, cc->order)).
>>
>> Arguably, testing for cc->order = -1 (or cc->order<  0) is
>> better anyway.
>
> I suppose it would be nicer to make the code in __compact_pgdat() match
> all the other places whcih do this:
>
> --- a/mm/compaction.c~mm-compaction-make-compact_control-order-signed-fix
> +++ a/mm/compaction.c
> @@ -686,7 +686,7 @@ static int __compact_pgdat(pg_data_t *pg
>   		INIT_LIST_HEAD(&cc->freepages);
>   		INIT_LIST_HEAD(&cc->migratepages);
>
> -		if (cc->order<  0 || !compaction_deferred(zone, cc->order))
> +		if (cc->order = -1 || !compaction_deferred(zone, cc->order))
>   			compact_zone(zone, cc);
>
>   		if (cc->order>  0) {

Agreed, with that and Dan's patch, things should all be
as expected.

-- 
All rights reversed

Re: [patch] mm: compaction: make compact_control order signed

[Rik van Riel]

On 02/01/2012 04:24 PM, Andrew Morton wrote:
> On Wed, 01 Feb 2012 16:17:10 -0500
> Rik van Riel<riel@redhat.com>  wrote:
>
>>>> @@ -35,7 +35,7 @@ struct compact_control {
>>>>    	unsigned long migrate_pfn;	/* isolate_migratepages search base */
>>>>    	bool sync;			/* Synchronous migration */
>>>>
>>>> -	unsigned int order;		/* order a direct compactor needs */
>>>> +	int order;			/* order a direct compactor needs */
>>>>    	int migratetype;		/* MOVABLE, RECLAIMABLE etc */
>>>>    	struct zone *zone;
>>>>    };
>>>
>>> One would expect this to significantly change the behaviour of
>>> /proc/sys/vm/compact_memory.  Enfeebled minds want to know: is
>>> the new behaviour better or worse than the old behaviour?
>>
>> The old behaviour and the behaviour post Dan's fix are the
>> same.
>>
>> My patch temporarily broke things, by testing for order<  0,
>> instead of the explicit cc->order == -1 used elsewhere in
>> the code.
>>
>> I did not notice it in my own testing because I tested on
>> 3.2.0 and sent you patches against 3.3-current. It looks
>> like this line of code is the one difference between both
>> trees I was working on :(
>>
>> In my test tree, I had (cc->sync || !compaction_deferred(zone, cc->order)).
>>
>> Arguably, testing for cc->order == -1 (or cc->order<  0) is
>> better anyway.
>
> I suppose it would be nicer to make the code in __compact_pgdat() match
> all the other places whcih do this:
>
> --- a/mm/compaction.c~mm-compaction-make-compact_control-order-signed-fix
> +++ a/mm/compaction.c
> @@ -686,7 +686,7 @@ static int __compact_pgdat(pg_data_t *pg
>   		INIT_LIST_HEAD(&cc->freepages);
>   		INIT_LIST_HEAD(&cc->migratepages);
>
> -		if (cc->order<  0 || !compaction_deferred(zone, cc->order))
> +		if (cc->order == -1 || !compaction_deferred(zone, cc->order))
>   			compact_zone(zone, cc);
>
>   		if (cc->order>  0) {

Agreed, with that and Dan's patch, things should all be
as expected.

-- 
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