On 5/9/2022 1:46 PM, Christophe Leroy wrote:
Le 08/05/2022 à 15:09, Baolin Wang a écrit :
On 5/8/2022 7:09 PM, Muchun Song wrote:
On Sun, May 08, 2022 at 05:36:39PM +0800, Baolin Wang wrote:
It is incorrect to use ptep_clear_flush() to nuke a hugetlb page
table when unmapping or migrating a hugetlb page, and will change
to use huge_ptep_clear_flush() instead in the following patches.
So this is a preparation patch, which changes the
huge_ptep_clear_flush()
to return the original pte to help to nuke a hugetlb page table.
Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
Acked-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Reviewed-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
Thanks for reviewing.
But one nit below:
[...]
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 8605d7e..61a21af 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -5342,7 +5342,7 @@ static vm_fault_t hugetlb_wp(struct mm_struct
*mm, struct vm_area_struct *vma,
ClearHPageRestoreReserve(new_page);
/* Break COW or unshare */
- huge_ptep_clear_flush(vma, haddr, ptep);
+ (void)huge_ptep_clear_flush(vma, haddr, ptep);
Why add a "(void)" here? Is there any warning if no "(void)"?
IIUC, I think we can remove this, right?
I did not meet any warning without the casting, but this is per Mike's
comment[1] to make the code consistent with other functions casting to
void type explicitly in hugetlb.c file.
[1]
https://lore.kernel.org/all/495c4ebe-a5b4-afb6-4cb0-956c1b18d0cc@xxxxxxxxxx/
As far as I understand, Mike said that you should be accompagnied with a
big fat comment explaining why we ignore the returned value from
huge_ptep_clear_flush(). >
By the way huge_ptep_clear_flush() is not declared 'must_check' so this
cast is just visual polution and should be removed.
In the meantime the comment suggested by Mike should be added instead.
Sorry for my misunderstanding. I just follow the explicit void casting
like other places in hugetlb.c file. And I am not sure if it is useful
adding some comments like below, since we did not need the original pte
value in the COW case mapping with a new page, and the code is more
readable already I think.
Mike, could you help to clarify what useful comments would you like? and
remove the explicit void casting? Thanks.
/*
* Just ignore the return value with new page mapped.
*/
