Re: [PATCH 5/5] mm/hugetlb: avoid calculating fault_mutex_hash in truncate_op case

[Miaohe Lin <linmiaohe@huawei.com>]

Hi:
On 2021/3/13 4:03, Mike Kravetz wrote:
> On 3/8/21 3:28 AM, Miaohe Lin wrote:
>> The fault_mutex hashing overhead can be avoided in truncate_op case because
>> page faults can not race with truncation in this routine. So calculate hash
>> for fault_mutex only in !truncate_op case to save some cpu cycles.
>>
>> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
>> ---
>>  fs/hugetlbfs/inode.c | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
>> index c262566f7c5d..d81f52b87bd7 100644
>> --- a/fs/hugetlbfs/inode.c
>> +++ b/fs/hugetlbfs/inode.c
>> @@ -482,10 +482,9 @@ static void remove_inode_hugepages(struct inode *inode, loff_t lstart,
>>  
>>  		for (i = 0; i < pagevec_count(&pvec); ++i) {
>>  			struct page *page = pvec.pages[i];
>> -			u32 hash;
>> +			u32 hash = 0;
> 
> Do we need to initialize hash here?
> I would not bring this up normally, but the purpose of the patch is to save
> cpu cycles.

The hash is initialized here in order to avoid false positive
"uninitialized local variable used" warning. Or this is indeed unnecessary?

Many thanks for review.

>