Convert two functions in hugetlb.c to use a folio

[PATCH 2/2] mm/hugetlb: Use a folio in hugetlb_wp()

Posted by Peng Zhang 2 years, 8 months ago

From: ZhangPeng <zhangpeng362@huawei.com>

We can replace nine implict calls to compound_head() with one by using
old_folio. However, we still need to keep old_page because we need to
know which page in the folio we are copying.

Suggested-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: ZhangPeng <zhangpeng362@huawei.com>
---
 mm/hugetlb.c | 22 ++++++++++++----------
 1 file changed, 12 insertions(+), 10 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 0b774dd3d57b..f0ab6e8adf6f 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -5543,6 +5543,7 @@ static vm_fault_t hugetlb_wp(struct mm_struct *mm, struct vm_area_struct *vma,
 	pte_t pte = huge_ptep_get(ptep);
 	struct hstate *h = hstate_vma(vma);
 	struct page *old_page;
+	struct folio *old_folio;
 	struct folio *new_folio;
 	int outside_reserve = 0;
 	vm_fault_t ret = 0;
@@ -5574,6 +5575,7 @@ static vm_fault_t hugetlb_wp(struct mm_struct *mm, struct vm_area_struct *vma,
 	}
 
 	old_page = pte_page(pte);
+	old_folio = page_folio(old_page);
 
 	delayacct_wpcopy_start();
 
@@ -5582,7 +5584,7 @@ static vm_fault_t hugetlb_wp(struct mm_struct *mm, struct vm_area_struct *vma,
 	 * If no-one else is actually using this page, we're the exclusive
 	 * owner and can reuse this page.
 	 */
-	if (page_mapcount(old_page) == 1 && PageAnon(old_page)) {
+	if (page_mapcount(old_page) == 1 && folio_test_anon(old_folio)) {
 		if (!PageAnonExclusive(old_page))
 			page_move_anon_rmap(old_page, vma);
 		if (likely(!unshare))
@@ -5591,8 +5593,8 @@ static vm_fault_t hugetlb_wp(struct mm_struct *mm, struct vm_area_struct *vma,
 		delayacct_wpcopy_end();
 		return 0;
 	}
-	VM_BUG_ON_PAGE(PageAnon(old_page) && PageAnonExclusive(old_page),
-		       old_page);
+	VM_BUG_ON_PAGE(folio_test_anon(old_folio) &&
+		       PageAnonExclusive(old_page), old_page);
 
 	/*
 	 * If the process that created a MAP_PRIVATE mapping is about to
@@ -5604,10 +5606,10 @@ static vm_fault_t hugetlb_wp(struct mm_struct *mm, struct vm_area_struct *vma,
 	 * of the full address range.
 	 */
 	if (is_vma_resv_set(vma, HPAGE_RESV_OWNER) &&
-			page_folio(old_page) != pagecache_folio)
+			old_folio != pagecache_folio)
 		outside_reserve = 1;
 
-	get_page(old_page);
+	folio_get(old_folio);
 
 	/*
 	 * Drop page table lock as buddy allocator may be called. It will
@@ -5629,7 +5631,7 @@ static vm_fault_t hugetlb_wp(struct mm_struct *mm, struct vm_area_struct *vma,
 			pgoff_t idx;
 			u32 hash;
 
-			put_page(old_page);
+			folio_put(old_folio);
 			/*
 			 * Drop hugetlb_fault_mutex and vma_lock before
 			 * unmapping.  unmapping needs to hold vma_lock
@@ -5674,7 +5676,7 @@ static vm_fault_t hugetlb_wp(struct mm_struct *mm, struct vm_area_struct *vma,
 		goto out_release_all;
 	}
 
-	if (copy_user_large_folio(new_folio, page_folio(old_page), address, vma)) {
+	if (copy_user_large_folio(new_folio, old_folio, address, vma)) {
 		ret = VM_FAULT_HWPOISON_LARGE;
 		goto out_release_all;
 	}
@@ -5703,7 +5705,7 @@ static vm_fault_t hugetlb_wp(struct mm_struct *mm, struct vm_area_struct *vma,
 		set_huge_pte_at(mm, haddr, ptep, newpte);
 		folio_set_hugetlb_migratable(new_folio);
 		/* Make the old page be freed below */
-		new_folio = page_folio(old_page);
+		new_folio = old_folio;
 	}
 	spin_unlock(ptl);
 	mmu_notifier_invalidate_range_end(&range);
@@ -5712,11 +5714,11 @@ static vm_fault_t hugetlb_wp(struct mm_struct *mm, struct vm_area_struct *vma,
 	 * No restore in case of successful pagetable update (Break COW or
 	 * unshare)
 	 */
-	if (new_folio != page_folio(old_page))
+	if (new_folio != old_folio)
 		restore_reserve_on_error(h, vma, haddr, new_folio);
 	folio_put(new_folio);
 out_release_old:
-	put_page(old_page);
+	folio_put(old_folio);
 
 	spin_lock(ptl); /* Caller expects lock to be held */
 
-- 
2.25.1

Re: [PATCH 2/2] mm/hugetlb: Use a folio in hugetlb_wp()

Posted by Matthew Wilcox 2 years, 8 months ago

On Fri, Jun 02, 2023 at 09:54:08AM +0800, Peng Zhang wrote:
> From: ZhangPeng <zhangpeng362@huawei.com>
> 
> We can replace nine implict calls to compound_head() with one by using
> old_folio. However, we still need to keep old_page because we need to
> know which page in the folio we are copying.

Do we?  It's my understanding (and I am far from an expert here ...)
that the 'pte_t *' we are passed *inside hugetlbfs* is not in fact a pte
pointer at all but actually a pmd or pud pointer.  See how we do this:

        pte_t pte = huge_ptep_get(ptep);

and so the page we get back is always a head page, and we can go
directly to a folio.  ie this is different from the THP cases.

Re: [PATCH 2/2] mm/hugetlb: Use a folio in hugetlb_wp()

Posted by zhangpeng (AS) 2 years, 8 months ago

On 2023/6/3 4:17, Matthew Wilcox wrote:

> On Fri, Jun 02, 2023 at 09:54:08AM +0800, Peng Zhang wrote:
>> From: ZhangPeng <zhangpeng362@huawei.com>
>>
>> We can replace nine implict calls to compound_head() with one by using
>> old_folio. However, we still need to keep old_page because we need to
>> know which page in the folio we are copying.
> Do we?  It's my understanding (and I am far from an expert here ...)
> that the 'pte_t *' we are passed *inside hugetlbfs* is not in fact a pte
> pointer at all but actually a pmd or pud pointer.  See how we do this:
>
>          pte_t pte = huge_ptep_get(ptep);
>
> and so the page we get back is always a head page, and we can go
> directly to a folio.  ie this is different from the THP cases.

Yes, I'll remove ptepage and old_page in a v2. Thanks.

Best Regards,
Peng

Re: [PATCH 2/2] mm/hugetlb: Use a folio in hugetlb_wp()

Posted by Mike Kravetz 2 years, 8 months ago

On 06/02/23 21:17, Matthew Wilcox wrote:
> On Fri, Jun 02, 2023 at 09:54:08AM +0800, Peng Zhang wrote:
> > From: ZhangPeng <zhangpeng362@huawei.com>
> > 
> > We can replace nine implict calls to compound_head() with one by using
> > old_folio. However, we still need to keep old_page because we need to
> > know which page in the folio we are copying.
> 
> Do we?  It's my understanding (and I am far from an expert here ...)
> that the 'pte_t *' we are passed *inside hugetlbfs* is not in fact a pte
> pointer at all but actually a pmd or pud pointer.

That may not be technically true in some arch specific cases such as
arm64 with CONT_PTES and CONT_PMDS.

>                                                    See how we do this:
> 
>         pte_t pte = huge_ptep_get(ptep);
> 
> and so the page we get back is always a head page, and we can go
> directly to a folio.  ie this is different from the THP cases.

However, it is true that ptep will always be associated with the head
page.  This is because the associated virtual address is hugetlb page
aligned.

So, I agree with Matthew that there is no need to keep old_page.
Note that if old_page was NOT the head page, then

	copy_user_huge_page(&new_folio->page, old_page, address, vma,
		pages_per_huge_page(h));

would write beyond the end of range as it assumes old_page is head.
-- 
Mike Kravetz

Re: [PATCH 2/2] mm/hugetlb: Use a folio in hugetlb_wp()

Posted by zhangpeng (AS) 2 years, 8 months ago

On 2023/6/3 4:52, Mike Kravetz wrote:

> On 06/02/23 21:17, Matthew Wilcox wrote:
>> On Fri, Jun 02, 2023 at 09:54:08AM +0800, Peng Zhang wrote:
>>> From: ZhangPeng <zhangpeng362@huawei.com>
>>>
>>> We can replace nine implict calls to compound_head() with one by using
>>> old_folio. However, we still need to keep old_page because we need to
>>> know which page in the folio we are copying.
>> Do we?  It's my understanding (and I am far from an expert here ...)
>> that the 'pte_t *' we are passed *inside hugetlbfs* is not in fact a pte
>> pointer at all but actually a pmd or pud pointer.
> That may not be technically true in some arch specific cases such as
> arm64 with CONT_PTES and CONT_PMDS.
>
>>                                                     See how we do this:
>>
>>          pte_t pte = huge_ptep_get(ptep);
>>
>> and so the page we get back is always a head page, and we can go
>> directly to a folio.  ie this is different from the THP cases.
> However, it is true that ptep will always be associated with the head
> page.  This is because the associated virtual address is hugetlb page
> aligned.
>
> So, I agree with Matthew that there is no need to keep old_page.
> Note that if old_page was NOT the head page, then
>
> 	copy_user_huge_page(&new_folio->page, old_page, address, vma,
> 		pages_per_huge_page(h));
>
> would write beyond the end of range as it assumes old_page is head.

Agreed. I'll send a v2 soon. Thanks.

Best Regards,
Peng

Re: [PATCH 2/2] mm/hugetlb: Use a folio in hugetlb_wp()

Posted by Sidhartha Kumar 2 years, 8 months ago

On 6/1/23 6:54 PM, Peng Zhang wrote:
> From: ZhangPeng <zhangpeng362@huawei.com>
> 
> We can replace nine implict calls to compound_head() with one by using
> old_folio. However, we still need to keep old_page because we need to
> know which page in the folio we are copying.
> 
> Suggested-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> Signed-off-by: ZhangPeng <zhangpeng362@huawei.com>
> ---
>   mm/hugetlb.c | 22 ++++++++++++----------
>   1 file changed, 12 insertions(+), 10 deletions(-)
> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 0b774dd3d57b..f0ab6e8adf6f 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -5543,6 +5543,7 @@ static vm_fault_t hugetlb_wp(struct mm_struct *mm, struct vm_area_struct *vma,
>   	pte_t pte = huge_ptep_get(ptep);
>   	struct hstate *h = hstate_vma(vma);
>   	struct page *old_page;
> +	struct folio *old_folio;
>   	struct folio *new_folio;
>   	int outside_reserve = 0;
>   	vm_fault_t ret = 0;
> @@ -5574,6 +5575,7 @@ static vm_fault_t hugetlb_wp(struct mm_struct *mm, struct vm_area_struct *vma,
>   	}
>   
>   	old_page = pte_page(pte);
> +	old_folio = page_folio(old_page);
>   
>   	delayacct_wpcopy_start();
>   
> @@ -5582,7 +5584,7 @@ static vm_fault_t hugetlb_wp(struct mm_struct *mm, struct vm_area_struct *vma,
>   	 * If no-one else is actually using this page, we're the exclusive
>   	 * owner and can reuse this page.
>   	 */
> -	if (page_mapcount(old_page) == 1 && PageAnon(old_page)) {
> +	if (page_mapcount(old_page) == 1 && folio_test_anon(old_folio)) {
>   		if (!PageAnonExclusive(old_page))
>   			page_move_anon_rmap(old_page, vma);
>   		if (likely(!unshare))
> @@ -5591,8 +5593,8 @@ static vm_fault_t hugetlb_wp(struct mm_struct *mm, struct vm_area_struct *vma,
>   		delayacct_wpcopy_end();
>   		return 0;
>   	}
> -	VM_BUG_ON_PAGE(PageAnon(old_page) && PageAnonExclusive(old_page),
> -		       old_page);
> +	VM_BUG_ON_PAGE(folio_test_anon(old_folio) &&
> +		       PageAnonExclusive(old_page), old_page);
>   
>   	/*
>   	 * If the process that created a MAP_PRIVATE mapping is about to
> @@ -5604,10 +5606,10 @@ static vm_fault_t hugetlb_wp(struct mm_struct *mm, struct vm_area_struct *vma,
>   	 * of the full address range.
>   	 */
>   	if (is_vma_resv_set(vma, HPAGE_RESV_OWNER) &&
> -			page_folio(old_page) != pagecache_folio)
> +			old_folio != pagecache_folio)
>   		outside_reserve = 1;
>   
> -	get_page(old_page);
> +	folio_get(old_folio);
>   
>   	/*
>   	 * Drop page table lock as buddy allocator may be called. It will
> @@ -5629,7 +5631,7 @@ static vm_fault_t hugetlb_wp(struct mm_struct *mm, struct vm_area_struct *vma,
>   			pgoff_t idx;
>   			u32 hash;
>   
> -			put_page(old_page);
> +			folio_put(old_folio);
>   			/*
>   			 * Drop hugetlb_fault_mutex and vma_lock before
>   			 * unmapping.  unmapping needs to hold vma_lock
> @@ -5674,7 +5676,7 @@ static vm_fault_t hugetlb_wp(struct mm_struct *mm, struct vm_area_struct *vma,
>   		goto out_release_all;
>   	}
>   
> -	if (copy_user_large_folio(new_folio, page_folio(old_page), address, vma)) {
> +	if (copy_user_large_folio(new_folio, old_folio, address, vma)) {
>   		ret = VM_FAULT_HWPOISON_LARGE;
>   		goto out_release_all;
>   	}
> @@ -5703,7 +5705,7 @@ static vm_fault_t hugetlb_wp(struct mm_struct *mm, struct vm_area_struct *vma,
>   		set_huge_pte_at(mm, haddr, ptep, newpte);
>   		folio_set_hugetlb_migratable(new_folio);
>   		/* Make the old page be freed below */
> -		new_folio = page_folio(old_page);
> +		new_folio = old_folio;
>   	}
>   	spin_unlock(ptl);
>   	mmu_notifier_invalidate_range_end(&range);
> @@ -5712,11 +5714,11 @@ static vm_fault_t hugetlb_wp(struct mm_struct *mm, struct vm_area_struct *vma,
>   	 * No restore in case of successful pagetable update (Break COW or
>   	 * unshare)
>   	 */
> -	if (new_folio != page_folio(old_page))
> +	if (new_folio != old_folio)
>   		restore_reserve_on_error(h, vma, haddr, new_folio);
>   	folio_put(new_folio);
>   out_release_old:
> -	put_page(old_page);
> +	folio_put(old_folio);
>   
>   	spin_lock(ptl); /* Caller expects lock to be held */
>   
Reviewed-by Sidhartha Kumar <sidhartha.kumar@oracle.com>

Re: [PATCH 2/2] mm/hugetlb: Use a folio in hugetlb_wp()

Posted by Muchun Song 2 years, 8 months ago


> On Jun 2, 2023, at 09:54, Peng Zhang <zhangpeng362@huawei.com> wrote:
> 
> From: ZhangPeng <zhangpeng362@huawei.com>
> 
> We can replace nine implict calls to compound_head() with one by using
> old_folio. However, we still need to keep old_page because we need to
> know which page in the folio we are copying.
> 
> Suggested-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> Signed-off-by: ZhangPeng <zhangpeng362@huawei.com>

Reviewed-by: Muchun Song <songmuchun@bytedance.com>

Thanks.