On 1/14/21 4:32 AM, David Hildenbrand wrote:
> On 14.01.21 12:31, Miaohe Lin wrote:
>> When gbl_reserve is 0, hugetlb_acct_memory() will do nothing except holding
>> and releasing hugetlb_lock.
>
> So, what's the deal then? Adding more code?
>
> If this is a performance improvement, we should spell it out. Otherwise
> I don't see a real benefit of this patch.
>
Thanks for finding/noticing this.
As David points out, the commit message should state that this is a
performance improvement. Mention that such a change avoids an unnecessary
hugetlb_lock lock/unlock cycle. You can also mention that this unnecessary
lock cycle is happening on 'most' hugetlb munmap operations.
>>
>> Signed-off-by: Miaohe Lin <linmia...@huawei.com>
>> ---
>> mm/hugetlb.c | 3 ++-
>> 1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
>> index 737b2dce19e6..fe2da9ad6233 100644
>> --- a/mm/hugetlb.c
>> +++ b/mm/hugetlb.c
>> @@ -5241,7 +5241,8 @@ long hugetlb_unreserve_pages(struct inode *inode, long
>> start, long end,
>> * reservations to be released may be adjusted.
>> */
>> gbl_reserve = hugepage_subpool_put_pages(spool, (chg - freed));
>> - hugetlb_acct_memory(h, -gbl_reserve);
>> + if (gbl_reserve)
>> + hugetlb_acct_memory(h, -gbl_reserve);
It is true that gbl_reserve is likely to be 0 in this code path. However,
there are other code paths where hugetlb_acct_memory is called with a delta
value of 0 as well. I would rather see a simple check at the beginning of
hugetlb_acct_memory like.
if (!delta)
return 0;
--
Mike Kravetz
>>
>> return 0;
>> }
>>
>
>
