On 2022/8/17 7:31, Mike Kravetz wrote:
> On 08/16/22 21:05, Miaohe Lin wrote:
>> When huge_add_to_page_cache() fails, the page is freed directly without
>> calling restore_reserve_on_error() to restore reserve for newly allocated
>> pages not in page cache. Fix this by calling restore_reserve_on_error()
>> when huge_add_to_page_cache fails.
>>
>> Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
>> ---
>> mm/hugetlb.c | 1 +
>> 1 file changed, 1 insertion(+)
>>
>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
>> index ff991e5bdf1f..b69d7808f457 100644
>> --- a/mm/hugetlb.c
>> +++ b/mm/hugetlb.c
>> @@ -5603,6 +5603,7 @@ static vm_fault_t hugetlb_no_page(struct mm_struct *mm,
>> if (vma->vm_flags & VM_MAYSHARE) {
>> int err = huge_add_to_page_cache(page, mapping, idx);
>> if (err) {
>> + restore_reserve_on_error(h, vma, haddr, page);
>
> Hmmmm. I was going to comment that restore_reserve_on_error would not handle
> the situation where 'err == -EEXIST' below. This is because it implies we
> raced with someone else that added the page to the cache. And, that other
Thanks for pointing this out.
> allocation, not this one, consumed the reservation. However, I am not sure
> how that could be possible? The hugetlb fault mutex (which we hold)
> must be held to add a page to the page cache.
>
> Searching git history I see that code was added (or at least existed) before
> the hugetlb fault mutex was introduced. So, I believe that check for -EEXIST
> and retry can go.
Agree with you. All call sites of huge_add_to_page_cache is protected by hugetlb fault mutex.
>
> With that said, restore_reserve_on_error can be called here. But, let's
> look into removing that err == -EEXIST check to avoid confusion.
Will do it in next version. Many thanks for your review and comment.
Thanks,
Miaohe Lin
