Re: [PATCH v2 1/2] mm: introduce memalloc_flags_move() for transferring allocation scopes

Re: [PATCH v2 1/2] mm: introduce memalloc_flags_move() for transferring allocation scopes

[Andrew Morton]

On Sun, 19 Jul 2026 17:57:31 +0800 Yun Zhou <yun.zhou@windriver.com> wrote:

> Add memalloc_flags_move() to transfer a saved memalloc scope from one
> tracking variable to another.  The source is zeroed so that a
> subsequent memalloc_flags_restore() on it becomes a no-op, effectively
> transferring ownership of the scope to the destination.
> 
> This is needed when a subsystem hands off an allocation context from
> one structure to another (e.g. during transaction rolling in
> filesystems), and needs to ensure the scope remains active without an
> extra save/restore cycle.
> 
> ...
>

Thanks.  fyi, Sashiko might have found a pre-existing xfs issue:
	https://sashiko.dev/#/patchset/20260719095732.1813590-1-yun.zhou@windriver.com

>  include/linux/sched/mm.h | 17 +++++++++++++++++
>  1 file changed, 17 insertions(+)

This file isn't mentioned in MAINTAINERS.  Could someone please propose
a patch?

From the MM side, probably just place it in every record which mentions
include/linux/mm.h - close enough.

> --- a/include/linux/sched/mm.h
> +++ b/include/linux/sched/mm.h
> @@ -342,6 +342,23 @@ static inline void memalloc_flags_restore(unsigned flags)
>  	current->flags &= ~flags;
>  }
>  
> +/**
> + * memalloc_flags_move - transfer a memalloc scope from one tracking
> + * variable to another.
> + * @old_flags: pointer to the source flags (will be zeroed)
> + *
> + * Returns the flags value to store in the destination.  The source is
> + * set to zero so that a subsequent memalloc_flags_restore() on it is
> + * a no-op.
> + */
> +static inline unsigned int memalloc_flags_move(unsigned int *old_flags)
> +{
> +	unsigned int ret = *old_flags;
> +
> +	*old_flags = 0;
> +	return ret;
> +}
> +

I've added linux-mm to cc here.  Please include it in any future
versions of this patchset.

Re: [PATCH v2 1/2] mm: introduce memalloc_flags_move() for transferring allocation scopes

[Zhou, Yun]

On 7/20/26 04:57, Andrew Morton wrote:
> On Sun, 19 Jul 2026 17:57:31 +0800 Yun Zhou <yun.zhou@windriver.com> wrote:
> 
>> Add memalloc_flags_move() to transfer a saved memalloc scope from one
>> tracking variable to another.  The source is zeroed so that a
>> subsequent memalloc_flags_restore() on it becomes a no-op, effectively
>> transferring ownership of the scope to the destination.
>>
>> This is needed when a subsystem hands off an allocation context from
>> one structure to another (e.g. during transaction rolling in
>> filesystems), and needs to ensure the scope remains active without an
>> extra save/restore cycle.
>>
>> ...
>>
> 
> Thanks.  fyi, Sashiko might have found a pre-existing xfs issue:
>          https://sashiko.dev/#/patchset/20260719095732.1813590-1-yun.zhou@windriver.com
> 

Good catch. This is indeed a pre-existing issue, and needs a separate fix.

>>   include/linux/sched/mm.h | 17 +++++++++++++++++
>>   1 file changed, 17 insertions(+)
> 
> This file isn't mentioned in MAINTAINERS.  Could someone please propose
> a patch?
> 
>  From the MM side, probably just place it in every record which mentions
> include/linux/mm.h - close enough.
> 
>> --- a/include/linux/sched/mm.h
>> +++ b/include/linux/sched/mm.h
>> @@ -342,6 +342,23 @@ static inline void memalloc_flags_restore(unsigned flags)
>>        current->flags &= ~flags;
>>   }
>>
>> +/**
>> + * memalloc_flags_move - transfer a memalloc scope from one tracking
>> + * variable to another.
>> + * @old_flags: pointer to the source flags (will be zeroed)
>> + *
>> + * Returns the flags value to store in the destination.  The source is
>> + * set to zero so that a subsequent memalloc_flags_restore() on it is
>> + * a no-op.
>> + */
>> +static inline unsigned int memalloc_flags_move(unsigned int *old_flags)
>> +{
>> +     unsigned int ret = *old_flags;
>> +
>> +     *old_flags = 0;
>> +     return ret;
>> +}
>> +
> 
> I've added linux-mm to cc here.  Please include it in any future
> versions of this patchset.
> 

Well, got it.

Thanks,
Yun