Re: [PATCH v2 2/6] mm: extract mm_prepare_for_swap_entries() helper

[Usama Arif]

On 06/07/2026 13:01, Kiryl Shutsemau wrote:
> On Mon, Jul 06, 2026 at 04:42:04AM -0700, Usama Arif wrote:
>> When a swap entry is installed in a page table, the mm must be added
>> to init_mm.mmlist so that swapoff can find and unuse its swap entries.
>> This double-checked locking pattern is currently open-coded in
>> try_to_unmap_one() and copy_nonpresent_pte().
>>
>> Move it into mm_prepare_for_swap_entries() in mm/internal.h and convert
>> both callers so it can be reused by upcoming PMD-level swap entry code
>> paths that also need to register the mm with swapoff.
>>
>> copy_nonpresent_pte() previously inserted into &src_mm->mmlist rather
>> than &init_mm.mmlist, but the insertion point is irrelevant, mmlist
>> is a circular list and swapoff walks it entirely from init_mm.mmlist,
>> so only membership matters, not position.
>>
>> Reviewed-by: Dev Jain <dev.jain@xxxxxxx>
>> Reviewed-by: Zi Yan <ziy@xxxxxxxxxx>
>> Acked-by: David Hildenbrand (Arm) <david@xxxxxxxxxx>
>> Signed-off-by: Usama Arif <usama.arif@xxxxxxxxx>
>> ---
>>  mm/internal.h | 10 ++++++++++
>>  mm/memory.c   |  9 +--------
>>  mm/rmap.c     |  7 +------
>>  3 files changed, 12 insertions(+), 14 deletions(-)
>>
>> diff --git a/mm/internal.h b/mm/internal.h
>> index 430aa72a4575..0360648e5726 100644
>> --- a/mm/internal.h
>> +++ b/mm/internal.h
>> @@ -1955,4 +1955,14 @@ static inline int get_sysctl_max_map_count(void)
>>  bool may_expand_vm(struct mm_struct *mm, const vma_flags_t *vma_flags,
>>  		   unsigned long npages);
>>  
>> +static inline void mm_prepare_for_swap_entries(struct mm_struct *mm)
>> +{
>> +	if (list_empty(&mm->mmlist)) {
>> +		spin_lock(&mmlist_lock);
>> +		if (list_empty(&mm->mmlist))
>> +			list_add(&mm->mmlist, &init_mm.mmlist);
> 
> The patch is fine, but the name of the field is awful. Seeing mmlist I
> assumed it listed all mm_structs. It has to have "swap" somewhere in the
> field name.
> 

I can send a separate patch once this is replaced to replace mmlist with
swap_mmlist if that sounds better?

Thanks
Usama