There is no need to execute the next loop if it not return in the first
loop. So add a break at the end of the loop.
At the same time, add !migratetype_is_mergeable() before the loop and
reduce the first index size from MIGRATE_TYPES to MIGRATE_PCPTYPES in
fallbacks array.
Signed-off-by: Yajun Deng <[email protected]>
Acked-by: Vlastimil Babka <[email protected]>
---
include/linux/mmzone.h | 2 +-
mm/page_alloc.c | 11 +++++------
2 files changed, 6 insertions(+), 7 deletions(-)
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index ab94985ee7d9..0a817b8c7fb2 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -85,7 +85,7 @@ static inline bool is_migrate_movable(int mt)
* Check whether a migratetype can be merged with another migratetype.
*
* It is only mergeable when it can fall back to other migratetypes for
- * allocation. See fallbacks[MIGRATE_TYPES][3] in page_alloc.c.
+ * allocation. See fallbacks[][] array in page_alloc.c.
*/
static inline bool migratetype_is_mergeable(int mt)
{
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 1113483fa6c5..536e8d838fb5 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2603,7 +2603,7 @@ struct page *__rmqueue_smallest(struct zone *zone, unsigned int order,
*
* The other migratetypes do not have fallbacks.
*/
-static int fallbacks[MIGRATE_TYPES][MIGRATE_PCPTYPES - 1] = {
+static int fallbacks[MIGRATE_PCPTYPES][MIGRATE_PCPTYPES - 1] = {
[MIGRATE_UNMOVABLE] = { MIGRATE_RECLAIMABLE, MIGRATE_MOVABLE },
[MIGRATE_MOVABLE] = { MIGRATE_RECLAIMABLE, MIGRATE_UNMOVABLE },
[MIGRATE_RECLAIMABLE] = { MIGRATE_UNMOVABLE, MIGRATE_MOVABLE },
@@ -2861,7 +2861,7 @@ int find_suitable_fallback(struct free_area *area, unsigned int order,
int i;
int fallback_mt;
- if (area->nr_free == 0)
+ if (area->nr_free == 0 || !migratetype_is_mergeable(migratetype))
return -1;
*can_steal = false;
@@ -2873,11 +2873,10 @@ int find_suitable_fallback(struct free_area *area, unsigned int order,
if (can_steal_fallback(order, migratetype))
*can_steal = true;
- if (!only_stealable)
- return fallback_mt;
-
- if (*can_steal)
+ if (!only_stealable || *can_steal)
return fallback_mt;
+ else
+ break;
}
return -1;
--
2.25.1
On 9 Feb 2023, at 5:11, Yajun Deng wrote:
> There is no need to execute the next loop if it not return in the first
> loop. So add a break at the end of the loop.
Can you explain why? If it is the case, MIGRATE_UNMOVABLE cannot fall back
to MIGRATE_MOVABLE? And MIGRATE_MOVABLE cannot fall back to MIGRATE_UNMOVABLE?
And MIGRATE_RECLAIMABLE cannot fall back to MIGRATE_MOVABLE?
>
> At the same time, add !migratetype_is_mergeable() before the loop and
> reduce the first index size from MIGRATE_TYPES to MIGRATE_PCPTYPES in
> fallbacks array.
You sent a patch: https://lore.kernel.org/all/[email protected]/T/#u, why not squash this one into that? Why do
we need two separate small patches working on the same code?
Thanks.
>
> Signed-off-by: Yajun Deng <[email protected]>
> Acked-by: Vlastimil Babka <[email protected]>
> ---
> include/linux/mmzone.h | 2 +-
> mm/page_alloc.c | 11 +++++------
> 2 files changed, 6 insertions(+), 7 deletions(-)
>
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index ab94985ee7d9..0a817b8c7fb2 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -85,7 +85,7 @@ static inline bool is_migrate_movable(int mt)
> * Check whether a migratetype can be merged with another migratetype.
> *
> * It is only mergeable when it can fall back to other migratetypes for
> - * allocation. See fallbacks[MIGRATE_TYPES][3] in page_alloc.c.
> + * allocation. See fallbacks[][] array in page_alloc.c.
> */
> static inline bool migratetype_is_mergeable(int mt)
> {
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 1113483fa6c5..536e8d838fb5 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -2603,7 +2603,7 @@ struct page *__rmqueue_smallest(struct zone *zone, unsigned int order,
> *
> * The other migratetypes do not have fallbacks.
> */
> -static int fallbacks[MIGRATE_TYPES][MIGRATE_PCPTYPES - 1] = {
> +static int fallbacks[MIGRATE_PCPTYPES][MIGRATE_PCPTYPES - 1] = {
> [MIGRATE_UNMOVABLE] = { MIGRATE_RECLAIMABLE, MIGRATE_MOVABLE },
> [MIGRATE_MOVABLE] = { MIGRATE_RECLAIMABLE, MIGRATE_UNMOVABLE },
> [MIGRATE_RECLAIMABLE] = { MIGRATE_UNMOVABLE, MIGRATE_MOVABLE },
> @@ -2861,7 +2861,7 @@ int find_suitable_fallback(struct free_area *area, unsigned int order,
> int i;
> int fallback_mt;
>
> - if (area->nr_free == 0)
> + if (area->nr_free == 0 || !migratetype_is_mergeable(migratetype))
> return -1;
>
> *can_steal = false;
> @@ -2873,11 +2873,10 @@ int find_suitable_fallback(struct free_area *area, unsigned int order,
> if (can_steal_fallback(order, migratetype))
> *can_steal = true;
>
> - if (!only_stealable)
> - return fallback_mt;
> -
> - if (*can_steal)
> + if (!only_stealable || *can_steal)
> return fallback_mt;
> + else
> + break;
> }
>
> return -1;
> --
> 2.25.1
--
Best Regards,
Yan, Zi
February 9, 2023 11:50 PM, "Zi Yan" <[email protected]> wrote:
> On 9 Feb 2023, at 5:11, Yajun Deng wrote:
>
>> There is no need to execute the next loop if it not return in the first
>> loop. So add a break at the end of the loop.
>
> Can you explain why? If it is the case, MIGRATE_UNMOVABLE cannot fall back
> to MIGRATE_MOVABLE? And MIGRATE_MOVABLE cannot fall back to MIGRATE_UNMOVABLE?
> And MIGRATE_RECLAIMABLE cannot fall back to MIGRATE_MOVABLE?
>
The return in the loop is only related to 'order', 'migratetype' and 'only_stealable'
variables. Even if it execute the next loop, it can't change the result. So the loop
can be broken if the first loop can't return.
>> At the same time, add !migratetype_is_mergeable() before the loop and
>> reduce the first index size from MIGRATE_TYPES to MIGRATE_PCPTYPES in
>> fallbacks array.
>
> You sent a patch: https://lore.kernel.org/all/[email protected]/T/#u,
> why not squash this one into that? Why do
> we need two separate small patches working on the same code?
>
Yes, this is better, but I overlooked this one when I sent the first patch. It is already merged.
As Vlastimil Babka said, reduce the first index from MIGRATE_TYPES to MIGRATE_PCPTYPES may be
cause out of bounds access of the shrinked fallbacks array If we don't judge the range of
migratetype. But this doesn't happen with the second index.
> Thanks.
>
>> Signed-off-by: Yajun Deng <[email protected]>
>> Acked-by: Vlastimil Babka <[email protected]>
>> ---
>> include/linux/mmzone.h | 2 +-
>> mm/page_alloc.c | 11 +++++------
>> 2 files changed, 6 insertions(+), 7 deletions(-)
>>
>> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
>> index ab94985ee7d9..0a817b8c7fb2 100644
>> --- a/include/linux/mmzone.h
>> +++ b/include/linux/mmzone.h
>> @@ -85,7 +85,7 @@ static inline bool is_migrate_movable(int mt)
>> * Check whether a migratetype can be merged with another migratetype.
>> *
>> * It is only mergeable when it can fall back to other migratetypes for
>> - * allocation. See fallbacks[MIGRATE_TYPES][3] in page_alloc.c.
>> + * allocation. See fallbacks[][] array in page_alloc.c.
>> */
>> static inline bool migratetype_is_mergeable(int mt)
>> {
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index 1113483fa6c5..536e8d838fb5 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -2603,7 +2603,7 @@ struct page *__rmqueue_smallest(struct zone *zone, unsigned int order,
>> *
>> * The other migratetypes do not have fallbacks.
>> */
>> -static int fallbacks[MIGRATE_TYPES][MIGRATE_PCPTYPES - 1] = {
>> +static int fallbacks[MIGRATE_PCPTYPES][MIGRATE_PCPTYPES - 1] = {
>> [MIGRATE_UNMOVABLE] = { MIGRATE_RECLAIMABLE, MIGRATE_MOVABLE },
>> [MIGRATE_MOVABLE] = { MIGRATE_RECLAIMABLE, MIGRATE_UNMOVABLE },
>> [MIGRATE_RECLAIMABLE] = { MIGRATE_UNMOVABLE, MIGRATE_MOVABLE },
>> @@ -2861,7 +2861,7 @@ int find_suitable_fallback(struct free_area *area, unsigned int order,
>> int i;
>> int fallback_mt;
>>
>> - if (area->nr_free == 0)
>> + if (area->nr_free == 0 || !migratetype_is_mergeable(migratetype))
>> return -1;
>>
>> *can_steal = false;
>> @@ -2873,11 +2873,10 @@ int find_suitable_fallback(struct free_area *area, unsigned int order,
>> if (can_steal_fallback(order, migratetype))
>> *can_steal = true;
>>
>> - if (!only_stealable)
>> - return fallback_mt;
>> -
>> - if (*can_steal)
>> + if (!only_stealable || *can_steal)
>> return fallback_mt;
>> + else
>> + break;
>> }
>>
>> return -1;
>> --
>> 2.25.1
>
> --
> Best Regards,
> Yan, Zi
On 9 Feb 2023, at 20:57, Yajun Deng wrote:
> February 9, 2023 11:50 PM, "Zi Yan" <[email protected]> wrote:
>
>> On 9 Feb 2023, at 5:11, Yajun Deng wrote:
>>
>>> There is no need to execute the next loop if it not return in the first
>>> loop. So add a break at the end of the loop.
>>
>> Can you explain why? If it is the case, MIGRATE_UNMOVABLE cannot fall back
>> to MIGRATE_MOVABLE? And MIGRATE_MOVABLE cannot fall back to MIGRATE_UNMOVABLE?
>> And MIGRATE_RECLAIMABLE cannot fall back to MIGRATE_MOVABLE?
>>
>
> The return in the loop is only related to 'order', 'migratetype' and 'only_stealable'
> variables. Even if it execute the next loop, it can't change the result. So the loop
> can be broken if the first loop can't return.
OK. Got it. Would the code below look better?
for (i = 0; i < MIGRATE_PCPTYPES - 1 ; i++) {
fallback_mt = fallbacks[migratetype][i];
if (free_area_empty(area, fallback_mt))
continue;
}
if (can_steal_fallback(order, migratetype))
*can_steal = true;
if (!only_stealable || *can_steal)
return fallback_mt;
return -1;
>
>>> At the same time, add !migratetype_is_mergeable() before the loop and
>>> reduce the first index size from MIGRATE_TYPES to MIGRATE_PCPTYPES in
>>> fallbacks array.
>>
>> You sent a patch: https://lore.kernel.org/all/[email protected]/T/#u,
>> why not squash this one into that? Why do
>> we need two separate small patches working on the same code?
>>
>
> Yes, this is better, but I overlooked this one when I sent the first patch. It is already merged.
>
> As Vlastimil Babka said, reduce the first index from MIGRATE_TYPES to MIGRATE_PCPTYPES may be
> cause out of bounds access of the shrinked fallbacks array If we don't judge the range of
> migratetype. But this doesn't happen with the second index.
>
>> Thanks.
>>
>>> Signed-off-by: Yajun Deng <[email protected]>
>>> Acked-by: Vlastimil Babka <[email protected]>
>>> ---
>>> include/linux/mmzone.h | 2 +-
>>> mm/page_alloc.c | 11 +++++------
>>> 2 files changed, 6 insertions(+), 7 deletions(-)
>>>
>>> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
>>> index ab94985ee7d9..0a817b8c7fb2 100644
>>> --- a/include/linux/mmzone.h
>>> +++ b/include/linux/mmzone.h
>>> @@ -85,7 +85,7 @@ static inline bool is_migrate_movable(int mt)
>>> * Check whether a migratetype can be merged with another migratetype.
>>> *
>>> * It is only mergeable when it can fall back to other migratetypes for
>>> - * allocation. See fallbacks[MIGRATE_TYPES][3] in page_alloc.c.
>>> + * allocation. See fallbacks[][] array in page_alloc.c.
>>> */
>>> static inline bool migratetype_is_mergeable(int mt)
>>> {
>>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>>> index 1113483fa6c5..536e8d838fb5 100644
>>> --- a/mm/page_alloc.c
>>> +++ b/mm/page_alloc.c
>>> @@ -2603,7 +2603,7 @@ struct page *__rmqueue_smallest(struct zone *zone, unsigned int order,
>>> *
>>> * The other migratetypes do not have fallbacks.
>>> */
>>> -static int fallbacks[MIGRATE_TYPES][MIGRATE_PCPTYPES - 1] = {
>>> +static int fallbacks[MIGRATE_PCPTYPES][MIGRATE_PCPTYPES - 1] = {
>>> [MIGRATE_UNMOVABLE] = { MIGRATE_RECLAIMABLE, MIGRATE_MOVABLE },
>>> [MIGRATE_MOVABLE] = { MIGRATE_RECLAIMABLE, MIGRATE_UNMOVABLE },
>>> [MIGRATE_RECLAIMABLE] = { MIGRATE_UNMOVABLE, MIGRATE_MOVABLE },
>>> @@ -2861,7 +2861,7 @@ int find_suitable_fallback(struct free_area *area, unsigned int order,
>>> int i;
>>> int fallback_mt;
>>>
>>> - if (area->nr_free == 0)
>>> + if (area->nr_free == 0 || !migratetype_is_mergeable(migratetype))
>>> return -1;
>>>
>>> *can_steal = false;
>>> @@ -2873,11 +2873,10 @@ int find_suitable_fallback(struct free_area *area, unsigned int order,
>>> if (can_steal_fallback(order, migratetype))
>>> *can_steal = true;
>>>
>>> - if (!only_stealable)
>>> - return fallback_mt;
>>> -
>>> - if (*can_steal)
>>> + if (!only_stealable || *can_steal)
>>> return fallback_mt;
>>> + else
>>> + break;
>>> }
>>>
>>> return -1;
>>> --
>>> 2.25.1
>>
>> --
>> Best Regards,
>> Yan, Zi
--
Best Regards,
Yan, Zi
February 10, 2023 10:14 AM, "Zi Yan" <[email protected]> wrote:
> On 9 Feb 2023, at 20:57, Yajun Deng wrote:
>
>> February 9, 2023 11:50 PM, "Zi Yan" <[email protected]> wrote:
>>
>>> On 9 Feb 2023, at 5:11, Yajun Deng wrote:
>>
>> There is no need to execute the next loop if it not return in the first
>> loop. So add a break at the end of the loop.
>>> Can you explain why? If it is the case, MIGRATE_UNMOVABLE cannot fall back
>>> to MIGRATE_MOVABLE? And MIGRATE_MOVABLE cannot fall back to MIGRATE_UNMOVABLE?
>>> And MIGRATE_RECLAIMABLE cannot fall back to MIGRATE_MOVABLE?
>>
>> The return in the loop is only related to 'order', 'migratetype' and 'only_stealable'
>> variables. Even if it execute the next loop, it can't change the result. So the loop
>> can be broken if the first loop can't return.
>
> OK. Got it. Would the code below look better?
>
> for (i = 0; i < MIGRATE_PCPTYPES - 1 ; i++) {
> fallback_mt = fallbacks[migratetype][i];
> if (free_area_empty(area, fallback_mt))
> continue;
> }
>
> if (can_steal_fallback(order, migratetype))
> *can_steal = true;
>
> if (!only_stealable || *can_steal)
> return fallback_mt;
>
> return -1;
>
Yes, I'll submit a v3 patch.
Thanks.
>> At the same time, add !migratetype_is_mergeable() before the loop and
>> reduce the first index size from MIGRATE_TYPES to MIGRATE_PCPTYPES in
>> fallbacks array.
>>> You sent a patch: https://lore.kernel.org/all/[email protected]/T/#u,
>>> why not squash this one into that? Why do
>>> we need two separate small patches working on the same code?
>>
>> Yes, this is better, but I overlooked this one when I sent the first patch. It is already merged.
>>
>> As Vlastimil Babka said, reduce the first index from MIGRATE_TYPES to MIGRATE_PCPTYPES may be
>> cause out of bounds access of the shrinked fallbacks array If we don't judge the range of
>> migratetype. But this doesn't happen with the second index.
>>
>>> Thanks.
>>
>> Signed-off-by: Yajun Deng <[email protected]>
>> Acked-by: Vlastimil Babka <[email protected]>
>> ---
>> include/linux/mmzone.h | 2 +-
>> mm/page_alloc.c | 11 +++++------
>> 2 files changed, 6 insertions(+), 7 deletions(-)
>>
>> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
>> index ab94985ee7d9..0a817b8c7fb2 100644
>> --- a/include/linux/mmzone.h
>> +++ b/include/linux/mmzone.h
>> @@ -85,7 +85,7 @@ static inline bool is_migrate_movable(int mt)
>> * Check whether a migratetype can be merged with another migratetype.
>> *
>> * It is only mergeable when it can fall back to other migratetypes for
>> - * allocation. See fallbacks[MIGRATE_TYPES][3] in page_alloc.c.
>> + * allocation. See fallbacks[][] array in page_alloc.c.
>> */
>> static inline bool migratetype_is_mergeable(int mt)
>> {
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index 1113483fa6c5..536e8d838fb5 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -2603,7 +2603,7 @@ struct page *__rmqueue_smallest(struct zone *zone, unsigned int order,
>> *
>> * The other migratetypes do not have fallbacks.
>> */
>> -static int fallbacks[MIGRATE_TYPES][MIGRATE_PCPTYPES - 1] = {
>> +static int fallbacks[MIGRATE_PCPTYPES][MIGRATE_PCPTYPES - 1] = {
>> [MIGRATE_UNMOVABLE] = { MIGRATE_RECLAIMABLE, MIGRATE_MOVABLE },
>> [MIGRATE_MOVABLE] = { MIGRATE_RECLAIMABLE, MIGRATE_UNMOVABLE },
>> [MIGRATE_RECLAIMABLE] = { MIGRATE_UNMOVABLE, MIGRATE_MOVABLE },
>> @@ -2861,7 +2861,7 @@ int find_suitable_fallback(struct free_area *area, unsigned int order,
>> int i;
>> int fallback_mt;
>>
>> - if (area->nr_free == 0)
>> + if (area->nr_free == 0 || !migratetype_is_mergeable(migratetype))
>> return -1;
>>
>> *can_steal = false;
>> @@ -2873,11 +2873,10 @@ int find_suitable_fallback(struct free_area *area, unsigned int order,
>> if (can_steal_fallback(order, migratetype))
>> *can_steal = true;
>>
>> - if (!only_stealable)
>> - return fallback_mt;
>> -
>> - if (*can_steal)
>> + if (!only_stealable || *can_steal)
>> return fallback_mt;
>> + else
>> + break;
>> }
>>
>> return -1;
>> --
>> 2.25.1
>>> --
>>> Best Regards,
>>> Yan, Zi
>
> --
> Best Regards,
> Yan, Zi
February 10, 2023 10:33 AM, "Yajun Deng" <[email protected]> wrote:
> February 10, 2023 10:14 AM, "Zi Yan" <[email protected]> wrote:
>
>> On 9 Feb 2023, at 20:57, Yajun Deng wrote:
>>
>>> February 9, 2023 11:50 PM, "Zi Yan" <[email protected]> wrote:
>>
>> On 9 Feb 2023, at 5:11, Yajun Deng wrote:
>>> There is no need to execute the next loop if it not return in the first
>>> loop. So add a break at the end of the loop.
>>
>> Can you explain why? If it is the case, MIGRATE_UNMOVABLE cannot fall back
>> to MIGRATE_MOVABLE? And MIGRATE_MOVABLE cannot fall back to MIGRATE_UNMOVABLE?
>> And MIGRATE_RECLAIMABLE cannot fall back to MIGRATE_MOVABLE?
>>> The return in the loop is only related to 'order', 'migratetype' and 'only_stealable'
>>> variables. Even if it execute the next loop, it can't change the result. So the loop
>>> can be broken if the first loop can't return.
>>
>> OK. Got it. Would the code below look better?
>>
>> for (i = 0; i < MIGRATE_PCPTYPES - 1 ; i++) {
>> fallback_mt = fallbacks[migratetype][i];
>> if (free_area_empty(area, fallback_mt))
>> continue;
>> }
>>
>> if (can_steal_fallback(order, migratetype))
>> *can_steal = true;
>>
>> if (!only_stealable || *can_steal)
>> return fallback_mt;
>>
>> return -1;
>
> Yes, I'll submit a v3 patch.
> Thanks.
>
I found a logical error in your code. It should be like this:
for (i = 0; i < MIGRATE_PCPTYPES - 1 ; i++) {
fallback_mt = fallbacks[migratetype][i];
if (!free_area_empty(area, fallback_mt))
break;
}
if (can_steal_fallback(order, migratetype))
*can_steal = true;
if (!only_stealable || *can_steal)
return fallback_mt;
return -1;
This code will modify the logic to the opposite.
So can anyone tell me if I should use this code or the v2 patch?
>>> At the same time, add !migratetype_is_mergeable() before the loop and
>>> reduce the first index size from MIGRATE_TYPES to MIGRATE_PCPTYPES in
>>> fallbacks array.
>>
>> You sent a patch: https://lore.kernel.org/all/[email protected]/T/#u,
>> why not squash this one into that? Why do
>> we need two separate small patches working on the same code?
>>> Yes, this is better, but I overlooked this one when I sent the first patch. It is already merged.
>>>
>>> As Vlastimil Babka said, reduce the first index from MIGRATE_TYPES to MIGRATE_PCPTYPES may be
>>> cause out of bounds access of the shrinked fallbacks array If we don't judge the range of
>>> migratetype. But this doesn't happen with the second index.
>>
>> Thanks.
>>> Signed-off-by: Yajun Deng <[email protected]>
>>> Acked-by: Vlastimil Babka <[email protected]>
>>> ---
>>> include/linux/mmzone.h | 2 +-
>>> mm/page_alloc.c | 11 +++++------
>>> 2 files changed, 6 insertions(+), 7 deletions(-)
>>>
>>> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
>>> index ab94985ee7d9..0a817b8c7fb2 100644
>>> --- a/include/linux/mmzone.h
>>> +++ b/include/linux/mmzone.h
>>> @@ -85,7 +85,7 @@ static inline bool is_migrate_movable(int mt)
>>> * Check whether a migratetype can be merged with another migratetype.
>>> *
>>> * It is only mergeable when it can fall back to other migratetypes for
>>> - * allocation. See fallbacks[MIGRATE_TYPES][3] in page_alloc.c.
>>> + * allocation. See fallbacks[][] array in page_alloc.c.
>>> */
>>> static inline bool migratetype_is_mergeable(int mt)
>>> {
>>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>>> index 1113483fa6c5..536e8d838fb5 100644
>>> --- a/mm/page_alloc.c
>>> +++ b/mm/page_alloc.c
>>> @@ -2603,7 +2603,7 @@ struct page *__rmqueue_smallest(struct zone *zone, unsigned int order,
>>> *
>>> * The other migratetypes do not have fallbacks.
>>> */
>>> -static int fallbacks[MIGRATE_TYPES][MIGRATE_PCPTYPES - 1] = {
>>> +static int fallbacks[MIGRATE_PCPTYPES][MIGRATE_PCPTYPES - 1] = {
>>> [MIGRATE_UNMOVABLE] = { MIGRATE_RECLAIMABLE, MIGRATE_MOVABLE },
>>> [MIGRATE_MOVABLE] = { MIGRATE_RECLAIMABLE, MIGRATE_UNMOVABLE },
>>> [MIGRATE_RECLAIMABLE] = { MIGRATE_UNMOVABLE, MIGRATE_MOVABLE },
>>> @@ -2861,7 +2861,7 @@ int find_suitable_fallback(struct free_area *area, unsigned int order,
>>> int i;
>>> int fallback_mt;
>>>
>>> - if (area->nr_free == 0)
>>> + if (area->nr_free == 0 || !migratetype_is_mergeable(migratetype))
>>> return -1;
>>>
>>> *can_steal = false;
>>> @@ -2873,11 +2873,10 @@ int find_suitable_fallback(struct free_area *area, unsigned int order,
>>> if (can_steal_fallback(order, migratetype))
>>> *can_steal = true;
>>>
>>> - if (!only_stealable)
>>> - return fallback_mt;
>>> -
>>> - if (*can_steal)
>>> + if (!only_stealable || *can_steal)
>>> return fallback_mt;
>>> + else
>>> + break;
>>> }
>>>
>>> return -1;
>>> --
>>> 2.25.1
>>
>> --
>> Best Regards,
>> Yan, Zi
>>
>> --
>> Best Regards,
>> Yan, Zi
On 2/10/23 03:51, Yajun Deng wrote:
> February 10, 2023 10:33 AM, "Yajun Deng" <[email protected]> wrote:
>
>> February 10, 2023 10:14 AM, "Zi Yan" <[email protected]> wrote:
>>
>>> On 9 Feb 2023, at 20:57, Yajun Deng wrote:
>>>
>>>> February 9, 2023 11:50 PM, "Zi Yan" <[email protected]> wrote:
>>>
>>> On 9 Feb 2023, at 5:11, Yajun Deng wrote:
>>>> There is no need to execute the next loop if it not return in the first
>>>> loop. So add a break at the end of the loop.
>>>
>>> Can you explain why? If it is the case, MIGRATE_UNMOVABLE cannot fall back
>>> to MIGRATE_MOVABLE? And MIGRATE_MOVABLE cannot fall back to MIGRATE_UNMOVABLE?
>>> And MIGRATE_RECLAIMABLE cannot fall back to MIGRATE_MOVABLE?
>>>> The return in the loop is only related to 'order', 'migratetype' and 'only_stealable'
>>>> variables. Even if it execute the next loop, it can't change the result. So the loop
>>>> can be broken if the first loop can't return.
>>>
>>> OK. Got it. Would the code below look better?
>>>
>>> for (i = 0; i < MIGRATE_PCPTYPES - 1 ; i++) {
>>> fallback_mt = fallbacks[migratetype][i];
>>> if (free_area_empty(area, fallback_mt))
>>> continue;
>>> }
>>>
>>> if (can_steal_fallback(order, migratetype))
>>> *can_steal = true;
>>>
>>> if (!only_stealable || *can_steal)
>>> return fallback_mt;
>>>
>>> return -1;
>>
>> Yes, I'll submit a v3 patch.
>> Thanks.
>>
>
> I found a logical error in your code. It should be like this:
>
> for (i = 0; i < MIGRATE_PCPTYPES - 1 ; i++) {
> fallback_mt = fallbacks[migratetype][i];
> if (!free_area_empty(area, fallback_mt))
> break;
> }
>
> if (can_steal_fallback(order, migratetype))
> *can_steal = true;
>
> if (!only_stealable || *can_steal)
> return fallback_mt;
>
> return -1;
>
> This code will modify the logic to the opposite.
It's still wrong, IMHO. If all fallbacks have free_area_empty(), it will
return the last one and not -1. Also will set *can_steal in such case.
> So can anyone tell me if I should use this code or the v2 patch?
Once that bugs are fixed, the result will probably not look much better than
v2, so I don't mind keeping v2.
February 10, 2023 3:58 PM, "Vlastimil Babka" <[email protected]> wrote:
> On 2/10/23 03:51, Yajun Deng wrote:
>
>> February 10, 2023 10:33 AM, "Yajun Deng" <[email protected]> wrote:
>>
>>> February 10, 2023 10:14 AM, "Zi Yan" <[email protected]> wrote:
>>
>> On 9 Feb 2023, at 20:57, Yajun Deng wrote:
>>
>> February 9, 2023 11:50 PM, "Zi Yan" <[email protected]> wrote:
>>
>> On 9 Feb 2023, at 5:11, Yajun Deng wrote:
>> There is no need to execute the next loop if it not return in the first
>> loop. So add a break at the end of the loop.
>>
>> Can you explain why? If it is the case, MIGRATE_UNMOVABLE cannot fall back
>> to MIGRATE_MOVABLE? And MIGRATE_MOVABLE cannot fall back to MIGRATE_UNMOVABLE?
>> And MIGRATE_RECLAIMABLE cannot fall back to MIGRATE_MOVABLE?
>> The return in the loop is only related to 'order', 'migratetype' and 'only_stealable'
>> variables. Even if it execute the next loop, it can't change the result. So the loop
>> can be broken if the first loop can't return.
>>
>> OK. Got it. Would the code below look better?
>>
>> for (i = 0; i < MIGRATE_PCPTYPES - 1 ; i++) {
>> fallback_mt = fallbacks[migratetype][i];
>> if (free_area_empty(area, fallback_mt))
>> continue;
>> }
>>
>> if (can_steal_fallback(order, migratetype))
>> *can_steal = true;
>>
>> if (!only_stealable || *can_steal)
>> return fallback_mt;
>>
>> return -1;
>>> Yes, I'll submit a v3 patch.
>>> Thanks.
>>
>> I found a logical error in your code. It should be like this:
>>
>> for (i = 0; i < MIGRATE_PCPTYPES - 1 ; i++) {
>> fallback_mt = fallbacks[migratetype][i];
>> if (!free_area_empty(area, fallback_mt))
>> break;
>> }
>>
>> if (can_steal_fallback(order, migratetype))
>> *can_steal = true;
>>
>> if (!only_stealable || *can_steal)
>> return fallback_mt;
>>
>> return -1;
>>
>> This code will modify the logic to the opposite.
>
> It's still wrong, IMHO. If all fallbacks have free_area_empty(), it will
> return the last one and not -1. Also will set *can_steal in such case.
>
Yes, you are right.
>> So can anyone tell me if I should use this code or the v2 patch?
>
> Once that bugs are fixed, the result will probably not look much better than
> v2, so I don't mind keeping v2.
I agree with that.