Messages in this thread | | | Subject | Re: [PATCH] mm/hugetlb: avoid unnecessary hugetlb_acct_memory() call | From | Mike Kravetz <> | Date | Thu, 14 Jan 2021 11:16:05 -0800 |
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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 <linmiaohe@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; >> } >> > >
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