Re: [PATCH] mm/thp: make set_huge_zero_page() return void

From: Ralph Campbell
Date: Tue Oct 01 2019 - 13:54:33 EST



On 10/1/19 4:52 AM, Kirill A. Shutemov wrote:
On Mon, Sep 30, 2019 at 12:55:28PM -0700, Ralph Campbell wrote:
The return value from set_huge_zero_page() is never checked so simplify
the code by making it return void.

Signed-off-by: Ralph Campbell <rcampbell@xxxxxxxxxx>
---
mm/huge_memory.c | 6 ++----
1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index c5cb6dcd6c69..6cf0ee65538d 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -686,20 +686,18 @@ static inline gfp_t alloc_hugepage_direct_gfpmask(struct vm_area_struct *vma)
}
/* Caller must hold page table lock. */
-static bool set_huge_zero_page(pgtable_t pgtable, struct mm_struct *mm,
+static void set_huge_zero_page(pgtable_t pgtable, struct mm_struct *mm,
struct vm_area_struct *vma, unsigned long haddr, pmd_t *pmd,
struct page *zero_page)
{
pmd_t entry;
- if (!pmd_none(*pmd))
- return false;
+

Wat? So you just bindly overwrite whatever is there?

NAK.

No, the only two places it is called from are do_huge_pmd_anonymous_page() which has the pmd_lock()
and already checked pmd_none() is true and
copy_huge_pmd() where the destination page table
is being filled in with no other threads accessing it.
I guess I should have put this analysis in the changelog.

Still, I guess putting a pmd_none() check in copy_huge_pmd()
as future proofing new callers of copy_huge_pmd() would
make sense.

entry = mk_pmd(zero_page, vma->vm_page_prot);
entry = pmd_mkhuge(entry);
if (pgtable)
pgtable_trans_huge_deposit(mm, pmd, pgtable);
set_pmd_at(mm, haddr, pmd, entry);
mm_inc_nr_ptes(mm);
- return true;
}
vm_fault_t do_huge_pmd_anonymous_page(struct vm_fault *vmf)
--
2.20.1