[PATCH] mm/hugetlb: Remove redundant VM_BUG_ON_PAGE on putback_active_hugepage()

[PATCH] mm/hugetlb: Remove redundant VM_BUG_ON_PAGE on putback_active_hugepage()

[Miaohe Lin]

PageHead(page) is implicitly checked in set_page_huge_active() via the
PageHeadHuge(page) check. So remove this explicit one.

Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
---
 mm/hugetlb.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 6cdb59d8f663..bbbe013a3a2d 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -5577,7 +5577,6 @@ bool isolate_huge_page(struct page *page, struct list_head *list)
 
 void putback_active_hugepage(struct page *page)
 {
-	VM_BUG_ON_PAGE(!PageHead(page), page);
 	spin_lock(&hugetlb_lock);
 	SetHPageMigratable(page);
 	list_move_tail(&page->lru, &(page_hstate(page))->hugepage_activelist);
-- 
2.19.1

Re: [PATCH] mm/hugetlb: Remove redundant VM_BUG_ON_PAGE on putback_active_hugepage()

[Mike Kravetz]

On 2/8/21 12:37 AM, Miaohe Lin wrote:
> PageHead(page) is implicitly checked in set_page_huge_active() via the
> PageHeadHuge(page) check. So remove this explicit one.

I do not disagree with the code change.  However, this commit message
is not accurate.  set_page_huge_active() no longer exists in the tree
you are changing.  It was replaced with SetHPageMigratable.  Also, the
VM_BUG_ON_PAGE(!PageHeadHuge(page), page) was removed in the process.
So, there is no redundant check.

However, a quick audit of calling code reveals that all callers know they
are operating on a hugetlb head page.
-- 
Mike Kravetz

> 
> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
> ---
>  mm/hugetlb.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 6cdb59d8f663..bbbe013a3a2d 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -5577,7 +5577,6 @@ bool isolate_huge_page(struct page *page, struct list_head *list)
>  
>  void putback_active_hugepage(struct page *page)
>  {
> -	VM_BUG_ON_PAGE(!PageHead(page), page);
>  	spin_lock(&hugetlb_lock);
>  	SetHPageMigratable(page);
>  	list_move_tail(&page->lru, &(page_hstate(page))->hugepage_activelist);
> 

Re: [PATCH] mm/hugetlb: Remove redundant VM_BUG_ON_PAGE on putback_active_hugepage()

[Miaohe Lin]

Hi:
On 2021/2/9 9:26, Mike Kravetz wrote:
> On 2/8/21 12:37 AM, Miaohe Lin wrote:
>> PageHead(page) is implicitly checked in set_page_huge_active() via the
>> PageHeadHuge(page) check. So remove this explicit one.
> 
> I do not disagree with the code change.  However, this commit message
> is not accurate.  set_page_huge_active() no longer exists in the tree
> you are changing.  It was replaced with SetHPageMigratable.  Also, the
> VM_BUG_ON_PAGE(!PageHeadHuge(page), page) was removed in the process.
> So, there is no redundant check.
> 
> However, a quick audit of calling code reveals that all callers know they
> are operating on a hugetlb head page.
> 

So I should change the commit log like:

	All callers know they are operating on a hugetlb head page. So this VM_BUG_ON_PAGE
	can't catch anything useful.

and send a v2. Right?

Re: [PATCH] mm/hugetlb: Remove redundant VM_BUG_ON_PAGE on putback_active_hugepage()

[Mike Kravetz]

On 2/8/21 6:10 PM, Miaohe Lin wrote:
> Hi:
> On 2021/2/9 9:26, Mike Kravetz wrote:
>> On 2/8/21 12:37 AM, Miaohe Lin wrote:
>>> PageHead(page) is implicitly checked in set_page_huge_active() via the
>>> PageHeadHuge(page) check. So remove this explicit one.
>>
>> I do not disagree with the code change.  However, this commit message
>> is not accurate.  set_page_huge_active() no longer exists in the tree
>> you are changing.  It was replaced with SetHPageMigratable.  Also, the
>> VM_BUG_ON_PAGE(!PageHeadHuge(page), page) was removed in the process.
>> So, there is no redundant check.
>>
>> However, a quick audit of calling code reveals that all callers know they
>> are operating on a hugetlb head page.
>>
> 
> So I should change the commit log like:
> 
> 	All callers know they are operating on a hugetlb head page. So this VM_BUG_ON_PAGE
> 	can't catch anything useful.
> 
> and send a v2. Right?

Correct,
-- 
Mike Kravetz

Re: [PATCH] mm/hugetlb: Remove redundant VM_BUG_ON_PAGE on putback_active_hugepage()

[Miaohe Lin]

Hi:
On 2021/2/9 11:39, Mike Kravetz wrote:
> On 2/8/21 6:10 PM, Miaohe Lin wrote:
>> Hi:
>> On 2021/2/9 9:26, Mike Kravetz wrote:
>>> On 2/8/21 12:37 AM, Miaohe Lin wrote:
>>>> PageHead(page) is implicitly checked in set_page_huge_active() via the
>>>> PageHeadHuge(page) check. So remove this explicit one.
>>>
>>> I do not disagree with the code change.  However, this commit message
>>> is not accurate.  set_page_huge_active() no longer exists in the tree
>>> you are changing.  It was replaced with SetHPageMigratable.  Also, the
>>> VM_BUG_ON_PAGE(!PageHeadHuge(page), page) was removed in the process.
>>> So, there is no redundant check.
>>>
>>> However, a quick audit of calling code reveals that all callers know they
>>> are operating on a hugetlb head page.
>>>
>>
>> So I should change the commit log like:
>>
>> 	All callers know they are operating on a hugetlb head page. So this VM_BUG_ON_PAGE
>> 	can't catch anything useful.
>>
>> and send a v2. Right?
> 
> Correct,
> 
Will do. Thanks a lot.