Re: [PATCH v3 2/3] vmalloc: Optimize vfree

[Usama Anjum]

<snip>
>> +void free_pages_bulk(struct page **page_array, unsigned long nr_pages)
>> +{
>> +	unsigned long start_pfn = 0, pfn;
>> +	unsigned long i, nr_contig = 0;
>> +
>> +	for (i = 0; i < nr_pages; i++) {
>> +		pfn = page_to_pfn(page_array[i]);
>> +		if (!nr_contig) {
>> +			start_pfn = pfn;
>> +			nr_contig = 1;
>> +		} else if (start_pfn + nr_contig != pfn) {
>> +			__free_contig_range(start_pfn, nr_contig);
>> +			start_pfn = pfn;
>> +			nr_contig = 1;
>> +			cond_resched();
>> +		} else {
>> +			nr_contig++;
>> +		}
>> +	}
>> +	if (nr_contig)
>> +		__free_contig_range(start_pfn, nr_contig);
>> +}
> 
> free_pages_bulk() assumes pages in page_array are sorted in PFN ascending order.
> I think it is worth documenting it, since without sorting, it can degrade
> back to the original implementation.
I'll add the kerneldoc comment.

> 
>> +
>>  /*
>>   * This is the 'heart' of the zoned buddy allocator.
>>   */
>> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
>> index c607307c657a6..e9b3d6451e48b 100644
>> --- a/mm/vmalloc.c
>> +++ b/mm/vmalloc.c
>> @@ -3459,19 +3459,13 @@ 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->flags & VM_MAP_PUT_PAGES)) {
>> +		for (i = 0; i < vm->nr_pages; i++)
>> +			mod_lruvec_page_state(vm->pages[i], NR_VMALLOC, -1);
>>  	}
>> +	free_pages_bulk(vm->pages, vm->nr_pages);
>> +
> 
> stats is updated before any page is freed. It is better to mention
> it in the commit message.
I'll mention it.

> 
>>  	kvfree(vm->pages);
>>  	kfree(vm);
>>  }
>> -- 
>> 2.47.3
> 
> Otherwise, LGTM.
> 
> Acked-by: Zi Yan <ziy@xxxxxxxxxx>
> 
> Best Regards,
> Yan, Zi
> 

Thanks,
Usama