Re: [PATCH v3 1/2] mm/vmalloc: extract vmalloc_free_pages() helper from vfree()

[Shivam Kalra]

On 11/03/26 23:04, Uladzislau Rezki wrote:
> On Mon, Mar 09, 2026 at 05:25:45PM +0530, Shivam Kalra via B4 Relay wrote:
>> From: Shivam Kalra <shivamkalra98@xxxxxxxxxxx>
>>
>> Extract the page-freeing loop and NR_VMALLOC stat accounting from
>> vfree() into a reusable vmalloc_free_pages() helper. The helper operates
>> on a range [start, end) of pages from a vm_struct, making it suitable
>> for both full free (vfree) and partial free (upcoming vrealloc shrink).
>>
>> No functional change.
>>
>> Signed-off-by: Shivam Kalra <shivamkalra98@xxxxxxxxxxx>
>> ---
>>  mm/vmalloc.c | 46 ++++++++++++++++++++++++++++++++--------------
>>  1 file changed, 32 insertions(+), 14 deletions(-)
>>
>> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
>> index c607307c657a..42ae68450a90 100644
>> --- a/mm/vmalloc.c
>> +++ b/mm/vmalloc.c
>> @@ -3416,6 +3416,36 @@ void vfree_atomic(const void *addr)
>>  		schedule_work(&p->wq);
>>  }
>>  
>> +/*
>> + * vmalloc_free_pages - free a range of pages from a vmalloc allocation
>> + * @vm: the vm_struct containing the pages
>> + * @start: first page index to free (inclusive)
>> + * @end: last page index to free (exclusive)
>> + *
>> + * Free pages [start, end) updating NR_VMALLOC stat accounting.
>> + * Caller is responsible for unmapping (vunmap_range) and KASAN
>> + * poisoning before calling this.
>> + */
>> +static void vmalloc_free_pages(struct vm_struct *vm, unsigned int start,
>> +			       unsigned int end)
>> +{
>> +	unsigned int i;
>> +
>> +	for (i = start; i < end; i++) {
>> +		struct page *page = vm->pages[i];
>> +
>> +		BUG_ON(!page);
>> +		/*
>> +		 * High-order allocs for huge vmallocs are split, so
>> +		 * can be freed as an array of order-0 allocations
>> +		 */
>> +		if (!(vm->flags & VM_MAP_PUT_PAGES))
>> +			mod_lruvec_page_state(page, NR_VMALLOC, -1);
>> +		__free_page(page);
>> +		cond_resched();
>> +	}
>> +}
>> +
>>  /**
>>   * vfree - Release memory allocated by vmalloc()
>>   * @addr:  Memory base address
>> @@ -3436,7 +3466,6 @@ void vfree_atomic(const void *addr)
>>  void vfree(const void *addr)
>>  {
>>  	struct vm_struct *vm;
>> -	int i;
>>  
>>  	if (unlikely(in_interrupt())) {
>>  		vfree_atomic(addr);
>> @@ -3459,19 +3488,8 @@ void vfree(const void *addr)
>>  
>>  	if (unlikely(vm->flags & VM_FLUSH_RESET_PERMS))
>>  		vm_reset_perms(vm);
>> -	for (i = 0; i < vm->nr_pages; i++) {
>> -		struct page *page = vm->pages[i];
>> -
>> -		BUG_ON(!page);
>> -		/*
>> -		 * High-order allocs for huge vmallocs are split, so
>> -		 * can be freed as an array of order-0 allocations
>> -		 */
>> -		if (!(vm->flags & VM_MAP_PUT_PAGES))
>> -			mod_lruvec_page_state(page, NR_VMALLOC, -1);
>> -		__free_page(page);
>> -		cond_resched();
>> -	}
>> +	if (vm->nr_pages)
>> +		vmalloc_free_pages(vm, 0, vm->nr_pages);
>>  	kvfree(vm->pages);
>>  	kfree(vm);
>>  }
>>
>> -- 
>> 2.43.0
>>
>>
> I posted my comment for the v2. Same here:
> 
> probably we should move "if (vm->nr_pages)" condition inside the
> vmalloc_free_pages().
> 
> I think, the function name should also be renamed to something like
> vm_area_free_pages() so we align with vm_area_alloc_pages() helper.
> 
> --
> Uladzislau Rezki
We might not even need this check, because nr_pages is zero and the
loop that runs inside the function would be a no-op, as end would
be zero.