[v5,1/6] userfaultfd: convert mfill_atomic_pte_copy() to use a folio

Commit Message

zhangpeng (AS) March 31, 2023, 9:39 a.m. UTC

From: ZhangPeng <[e-mail]>

Call vma_alloc_folio() directly instead of alloc_page_vma() and convert
page_kaddr to kaddr in mfill_atomic_pte_copy(). Removes several calls to
compound_head().

Signed-off-by: ZhangPeng <[e-mail]>
Reviewed-by: Sidhartha Kumar <[e-mail]>
---
 mm/userfaultfd.c | 33 +++++++++++++++++----------------
 1 file changed, 17 insertions(+), 16 deletions(-)

Comments

Mike Kravetz April 6, 2023, 9:31 p.m. UTC | #1

On 03/31/23 17:39, Peng Zhang wrote:
> From: ZhangPeng <[e-mail]>
> 
> Call vma_alloc_folio() directly instead of alloc_page_vma() and convert
> page_kaddr to kaddr in mfill_atomic_pte_copy(). Removes several calls to
> compound_head().
> 
> Signed-off-by: ZhangPeng <[e-mail]>
> Reviewed-by: Sidhartha Kumar <[e-mail]>
> ---
>  mm/userfaultfd.c | 33 +++++++++++++++++----------------
>  1 file changed, 17 insertions(+), 16 deletions(-)

Looks good,

Reviewed-by: Mike Kravetz <[e-mail]>

>  	} else {
> -		page = *pagep;
> +		folio = page_folio(*pagep);
> +		VM_BUG_ON_FOLIO(folio_test_large(folio), folio);
>  		*pagep = NULL;
>  	}

However, I am still unsure about the reason for adding the VM_BUG_ON_FOLIO
here.

zhangpeng (AS) April 8, 2023, 4:42 a.m. UTC | #2

On 2023/4/7 5:31, Mike Kravetz wrote:

> On 03/31/23 17:39, Peng Zhang wrote:
>> From: ZhangPeng <[e-mail]>
>>
>> Call vma_alloc_folio() directly instead of alloc_page_vma() and convert
>> page_kaddr to kaddr in mfill_atomic_pte_copy(). Removes several calls to
>> compound_head().
>>
>> Signed-off-by: ZhangPeng <[e-mail]>
>> Reviewed-by: Sidhartha Kumar <[e-mail]>
>> ---
>>   mm/userfaultfd.c | 33 +++++++++++++++++----------------
>>   1 file changed, 17 insertions(+), 16 deletions(-)
> Looks good,
>
> Reviewed-by: Mike Kravetz <[e-mail]>
>
>>   	} else {
>> -		page = *pagep;
>> +		folio = page_folio(*pagep);
>> +		VM_BUG_ON_FOLIO(folio_test_large(folio), folio);
>>   		*pagep = NULL;
>>   	}
> However, I am still unsure about the reason for adding the VM_BUG_ON_FOLIO
> here.

VM_BUG_ON_FOLIO was added to ensure that folio is a single-page folio.
However, the folio corresponding to the foliop is always a single-page
folio. We just don't need this check. I'll drop VM_BUG_ON_FOLIO.

Thanks for your review.

Best Regards,
Peng

Patch

diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index 7f1b5f8b712c..24d6ed7ff302 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -135,17 +135,18 @@  static int mfill_atomic_pte_copy(pmd_t *dst_pmd,
 				 uffd_flags_t flags,
 				 struct page **pagep)
 {
-	void *page_kaddr;
+	void *kaddr;
 	int ret;
-	struct page *page;
+	struct folio *folio;
 
 	if (!*pagep) {
 		ret = -ENOMEM;
-		page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, dst_vma, dst_addr);
-		if (!page)
+		folio = vma_alloc_folio(GFP_HIGHUSER_MOVABLE, 0, dst_vma,
+					dst_addr, false);
+		if (!folio)
 			goto out;
 
-		page_kaddr = kmap_local_page(page);
+		kaddr = kmap_local_folio(folio, 0);
 		/*
 		 * The read mmap_lock is held here.  Despite the
 		 * mmap_lock being read recursive a deadlock is still
@@ -162,45 +163,45 @@  static int mfill_atomic_pte_copy(pmd_t *dst_pmd,
 		 * and retry the copy outside the mmap_lock.
 		 */
 		pagefault_disable();
-		ret = copy_from_user(page_kaddr,
-				     (const void __user *) src_addr,
+		ret = copy_from_user(kaddr, (const void __user *) src_addr,
 				     PAGE_SIZE);
 		pagefault_enable();
-		kunmap_local(page_kaddr);
+		kunmap_local(kaddr);
 
 		/* fallback to copy_from_user outside mmap_lock */
 		if (unlikely(ret)) {
 			ret = -ENOENT;
-			*pagep = page;
+			*pagep = &folio->page;
 			/* don't free the page */
 			goto out;
 		}
 
-		flush_dcache_page(page);
+		flush_dcache_folio(folio);
 	} else {
-		page = *pagep;
+		folio = page_folio(*pagep);
+		VM_BUG_ON_FOLIO(folio_test_large(folio), folio);
 		*pagep = NULL;
 	}
 
 	/*
-	 * The memory barrier inside __SetPageUptodate makes sure that
+	 * The memory barrier inside __folio_mark_uptodate makes sure that
 	 * preceding stores to the page contents become visible before
 	 * the set_pte_at() write.
 	 */
-	__SetPageUptodate(page);
+	__folio_mark_uptodate(folio);
 
 	ret = -ENOMEM;
-	if (mem_cgroup_charge(page_folio(page), dst_vma->vm_mm, GFP_KERNEL))
+	if (mem_cgroup_charge(folio, dst_vma->vm_mm, GFP_KERNEL))
 		goto out_release;
 
 	ret = mfill_atomic_install_pte(dst_pmd, dst_vma, dst_addr,
-				       page, true, flags);
+				       &folio->page, true, flags);
 	if (ret)
 		goto out_release;
 out:
 	return ret;
 out_release:
-	put_page(page);
+	folio_put(folio);
 	goto out;
 }