Hi: On 2021/1/22 3:00, Mike Kravetz wrote: > On 1/20/21 1:23 AM, Miaohe Lin wrote: >> The calculation 1U << (h->order + PAGE_SHIFT - 10) is actually equal to >> (PAGE_SHIFT << (h->order)) >> 10. So we can make it more readable by >> replace it with huge_page_size(h) / SZ_1K. >> >> Signed-off-by: Miaohe Lin <[email protected]> >> --- >> 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 25c1857ff45d..f94b8f6553fa 100644 >> --- a/fs/hugetlbfs/inode.c >> +++ b/fs/hugetlbfs/inode.c >> @@ -1519,8 +1519,8 @@ static struct vfsmount *__init >> mount_one_hugetlbfs(struct hstate *h) >> put_fs_context(fc); >> } >> if (IS_ERR(mnt)) >> - pr_err("Cannot mount internal hugetlbfs for page size %uK", >> - 1U << (h->order + PAGE_SHIFT - 10)); >> + pr_err("Cannot mount internal hugetlbfs for page size %luK", >> + huge_page_size(h) / SZ_1K); > > I appreciate the effort to make the code more readable. The existing > calculation does take a minute to understand. However, it is correct and > anyone modifying the code should be able to understand. > > With my compiler, your proposed change adds an additional instruction to > the routine mount_one_hugetlbfs. I know this is not significant, but still
I thought compiler would generate the same code... > it does increase the kernel size for a change that is of questionable value. > > In the kernel, size in KB is often calculated as (size << (PAGE_SHIFT - 10)). > If you change the calculation in the hugetlb code to be: > > huge_page_size(h) << (PAGE_SHIFT - 10) I'am sorry but this looks not really correct. I think the calculation shoud be huge_page_size(h) >> 10. What do you think? > > my compiler will actually reduce the size of the routine by one instruction. > Many thanks.
