On Thu, Feb 10, 2022 at 10:17:29PM +0800, Miaohe Lin wrote:
> orig_head is used to check whether the page have changed compound pages
> during the locking. But it's always equal to hpage. So we can use hpage
> directly and remove this redundant one.
>
> Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
> ---
> mm/memory-failure.c | 5 ++---
> 1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index 2dd7f35ee65a..4370c2f407c5 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -1691,7 +1691,6 @@ int memory_failure(unsigned long pfn, int flags)
> {
> struct page *p;
> struct page *hpage;
> - struct page *orig_head;
> struct dev_pagemap *pgmap;
> int res = 0;
> unsigned long page_flags;
> @@ -1737,7 +1736,7 @@ int memory_failure(unsigned long pfn, int flags)
> goto unlock_mutex;
> }
>
> - orig_head = hpage = compound_head(p);
> + hpage = compound_head(p);
> num_poisoned_pages_inc();
>
> /*
> @@ -1821,7 +1820,7 @@ int memory_failure(unsigned long pfn, int flags)
> * The page could have changed compound pages during the locking.
> * If this happens just bail out.
> */
> - if (PageCompound(p) && compound_head(p) != orig_head) {
> + if (PageCompound(p) && compound_head(p) != hpage) {
I think that this if-check was intended to detect the case that page p
belongs to a thp when memory_failure() is called and belongs to a compound
page in different size (like slab or some driver page) after the thp is
split. But your suggestion makes me aware that the page p could be embedded
on a thp again after thp split. I think this might be rare, but if it
happens the current if-check (or suggested one) cannot detect it.
So I feel that simply dropping compound_head() check might be better?
- if (PageCompound(p) && compound_head(p) != orig_head) {
+ if (PageCompound(p)) {
This should ensure the assumption (mentioned in 8/8 patch) more that
the error page never belongs to compound page after taking page lock.
Thanks,
Naoya Horiguchi
