Hi: On 2021/1/15 3:16, Mike Kravetz wrote: > 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. > My bad. I should spell this out explicitly. Many thanks for both of you. >>> >>> Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx> >>> --- >>> 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; > Sounds good. Will do it in v2. Many thanks again.
