Re: [PATCH v5 1/3] mm/vmalloc: extract vm_area_free_pages() helper from vfree()

[Shivam Kalra <shivamkalra98@zohomail.in>]

On 18/03/26 23:23, Uladzislau Rezki wrote:
> On Tue, Mar 17, 2026 at 01:47:33PM +0530, Shivam Kalra via B4 Relay wrote:
>> From: Shivam Kalra <shivamkalra98@zohomail.in>
>>
>> Extract the page-freeing loop and NR_VMALLOC stat accounting from
>> vfree() into a reusable vm_area_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).
>>
>> Freed page pointers in vm->pages[] are set to NULL to prevent stale
>> references when the vm_struct outlives the free (as in vrealloc shrink).
>>
>> Signed-off-by: Shivam Kalra <shivamkalra98@zohomail.in>
>> ---
>>  mm/vmalloc.c | 47 +++++++++++++++++++++++++++++++++--------------
>>  1 file changed, 33 insertions(+), 14 deletions(-)
>>
>> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
>> index c607307c657a..b29bf58c0e3f 100644
>> --- a/mm/vmalloc.c
>> +++ b/mm/vmalloc.c
>> @@ -3416,6 +3416,38 @@ void vfree_atomic(const void *addr)
>>  		schedule_work(&p->wq);
>>  }
>>  
>> +/*
>> + * vm_area_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.
>> + * Freed vm->pages[] entries are set to NULL.
>> + * Caller is responsible for unmapping (vunmap_range) and KASAN
>> + * poisoning before calling this.
>> + */
>> +static void vm_area_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);
>> +		vm->pages[i] = NULL;
>> +		cond_resched();
>> +	}
>> +}
>> +
>>
> Since you will update second patch, probably you can also improve this
> one. To me start/end variables sound like a VA range whereas it is
> indices in the array.
> 
> Any thoughts?
> 
> --
> Uladzislau Rezki
Oops, replied to the wrong thread! But regarding start/end, yes you're
absolutely right. I will rename them to start_idx and end_idx to make it
clear they are array indices in the next version