[PATCH 0/3] Use folios for symlinks in the page cache

[PATCH 0/3] Use folios for symlinks in the page cache

[Matthew Wilcox (Oracle)]

FUSE already uses folios for its symlinks.  Mirror that conversion in
the generic code and the NFS code.  That lets us get rid of a few
folio->page->folio conversions in this path, and some of the few
remaining users of read_cache_page() / read_mapping_page().

If anyone's concerned about all the extra lines in the diffstat, it's
documentation that I've added.

Matthew Wilcox (Oracle) (3):
  fs: Convert __page_get_link() to use a folio
  nfs: Use a folio in nfs_get_link()
  fs: Pass a folio to page_put_link()

 fs/fuse/dir.c    |  2 +-
 fs/namei.c       | 48 ++++++++++++++++++++++++++++++++++++------------
 fs/nfs/symlink.c | 20 ++++++++++----------
 3 files changed, 47 insertions(+), 23 deletions(-)

-- 
2.47.2

[PATCH 1/3] fs: Convert __page_get_link() to use a folio

[Matthew Wilcox (Oracle)]

Retrieve a folio from the page cache instead of a page and operate
on it.  Removes two hidden calls to compound_head().

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 fs/namei.c | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index 84a0e0b0111c..8e82aa7ecb82 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -5403,25 +5403,25 @@ EXPORT_SYMBOL(vfs_get_link);
 static char *__page_get_link(struct dentry *dentry, struct inode *inode,
 			     struct delayed_call *callback)
 {
-	struct page *page;
+	struct folio *folio;
 	struct address_space *mapping = inode->i_mapping;
 
 	if (!dentry) {
-		page = find_get_page(mapping, 0);
-		if (!page)
+		folio = filemap_get_folio(mapping, 0);
+		if (IS_ERR(folio))
 			return ERR_PTR(-ECHILD);
-		if (!PageUptodate(page)) {
-			put_page(page);
+		if (!folio_test_uptodate(folio)) {
+			folio_put(folio);
 			return ERR_PTR(-ECHILD);
 		}
 	} else {
-		page = read_mapping_page(mapping, 0, NULL);
-		if (IS_ERR(page))
-			return (char*)page;
+		folio = read_mapping_folio(mapping, 0, NULL);
+		if (IS_ERR(folio))
+			return ERR_CAST(folio);
 	}
-	set_delayed_call(callback, page_put_link, page);
+	set_delayed_call(callback, page_put_link, &folio->page);
 	BUG_ON(mapping_gfp_mask(mapping) & __GFP_HIGHMEM);
-	return page_address(page);
+	return folio_address(folio);
 }
 
 const char *page_get_link_raw(struct dentry *dentry, struct inode *inode,
-- 
2.47.2

[PATCH 2/3] nfs: Use a folio in nfs_get_link()

[Matthew Wilcox (Oracle)]

Mirror the changes to __page_get_link() by retrieving a folio from
the page cache instead of a page.  Removes two hidden calls to
compound_head().

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 fs/nfs/symlink.c | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/fs/nfs/symlink.c b/fs/nfs/symlink.c
index 1c62a5a9f51d..004a8f6c568e 100644
--- a/fs/nfs/symlink.c
+++ b/fs/nfs/symlink.c
@@ -40,31 +40,31 @@ static const char *nfs_get_link(struct dentry *dentry,
 				struct inode *inode,
 				struct delayed_call *done)
 {
-	struct page *page;
+	struct folio *folio;
 	void *err;
 
 	if (!dentry) {
 		err = ERR_PTR(nfs_revalidate_mapping_rcu(inode));
 		if (err)
 			return err;
-		page = find_get_page(inode->i_mapping, 0);
-		if (!page)
+		folio = filemap_get_folio(inode->i_mapping, 0);
+		if (IS_ERR(folio))
 			return ERR_PTR(-ECHILD);
-		if (!PageUptodate(page)) {
-			put_page(page);
+		if (!folio_test_uptodate(folio)) {
+			folio_put(folio);
 			return ERR_PTR(-ECHILD);
 		}
 	} else {
 		err = ERR_PTR(nfs_revalidate_mapping(inode, inode->i_mapping));
 		if (err)
 			return err;
-		page = read_cache_page(&inode->i_data, 0, nfs_symlink_filler,
+		folio = read_cache_folio(&inode->i_data, 0, nfs_symlink_filler,
 				NULL);
-		if (IS_ERR(page))
-			return ERR_CAST(page);
+		if (IS_ERR(folio))
+			return ERR_CAST(folio);
 	}
-	set_delayed_call(done, page_put_link, page);
-	return page_address(page);
+	set_delayed_call(done, page_put_link, &folio->page);
+	return folio_address(folio);
 }
 
 /*
-- 
2.47.2

[PATCH 3/3] fs: Pass a folio to page_put_link()

[Matthew Wilcox (Oracle)]

All callers now have a folio.  Pass it to page_put_link(), saving a
hidden call to compound_head().  Also add kernel-doc for page_get_link()
and page_put_link().

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 fs/fuse/dir.c    |  2 +-
 fs/namei.c       | 30 +++++++++++++++++++++++++++---
 fs/nfs/symlink.c |  2 +-
 3 files changed, 29 insertions(+), 5 deletions(-)

diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
index 83ac192e7fdd..33b82529cb6e 100644
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -1676,7 +1676,7 @@ static const char *fuse_get_link(struct dentry *dentry, struct inode *inode,
 		goto out_err;
 	}
 
-	set_delayed_call(callback, page_put_link, &folio->page);
+	set_delayed_call(callback, page_put_link, folio);
 
 	return folio_address(folio);
 
diff --git a/fs/namei.c b/fs/namei.c
index 8e82aa7ecb82..12d24f6da782 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -5419,7 +5419,7 @@ static char *__page_get_link(struct dentry *dentry, struct inode *inode,
 		if (IS_ERR(folio))
 			return ERR_CAST(folio);
 	}
-	set_delayed_call(callback, page_put_link, &folio->page);
+	set_delayed_call(callback, page_put_link, folio);
 	BUG_ON(mapping_gfp_mask(mapping) & __GFP_HIGHMEM);
 	return folio_address(folio);
 }
@@ -5431,6 +5431,17 @@ const char *page_get_link_raw(struct dentry *dentry, struct inode *inode,
 }
 EXPORT_SYMBOL_GPL(page_get_link_raw);
 
+/**
+ * page_get_link() - An implementation of the get_link inode_operation.
+ * @dentry: The directory entry which is the symlink.
+ * @inode: The inode for the symlink.
+ * @callback: Used to drop the reference to the symlink.
+ *
+ * Filesystems which store their symlinks in the page cache should use
+ * this to implement the get_link() member of their inode_operations.
+ *
+ * Return: A pointer to the NUL-terminated symlink.
+ */
 const char *page_get_link(struct dentry *dentry, struct inode *inode,
 					struct delayed_call *callback)
 {
@@ -5440,12 +5451,25 @@ const char *page_get_link(struct dentry *dentry, struct inode *inode,
 		nd_terminate_link(kaddr, inode->i_size, PAGE_SIZE - 1);
 	return kaddr;
 }
-
 EXPORT_SYMBOL(page_get_link);
 
+/**
+ * page_put_link() - Drop the reference to the symlink.
+ * @arg: The folio which contains the symlink.
+ *
+ * This is used internally by page_get_link().  It is exported for use
+ * by filesystems which need to implement a variant of page_get_link()
+ * themselves.  Despite the apparent symmetry, filesystems which use
+ * page_get_link() do not need to call page_put_link().
+ *
+ * The argument, while it has a void pointer type, must be a pointer to
+ * the folio which was retrieved from the page cache.  The delayed_call
+ * infrastructure is used to drop the reference count once the caller
+ * is done with the symlink.
+ */
 void page_put_link(void *arg)
 {
-	put_page(arg);
+	folio_put(arg);
 }
 EXPORT_SYMBOL(page_put_link);
 
diff --git a/fs/nfs/symlink.c b/fs/nfs/symlink.c
index 004a8f6c568e..58146e935402 100644
--- a/fs/nfs/symlink.c
+++ b/fs/nfs/symlink.c
@@ -63,7 +63,7 @@ static const char *nfs_get_link(struct dentry *dentry,
 		if (IS_ERR(folio))
 			return ERR_CAST(folio);
 	}
-	set_delayed_call(done, page_put_link, &folio->page);
+	set_delayed_call(done, page_put_link, folio);
 	return folio_address(folio);
 }
 
-- 
2.47.2

Re: [PATCH 0/3] Use folios for symlinks in the page cache

[Christian Brauner]

On Wed, 14 May 2025 18:13:11 +0100, Matthew Wilcox (Oracle) wrote:
> FUSE already uses folios for its symlinks.  Mirror that conversion in
> the generic code and the NFS code.  That lets us get rid of a few
> folio->page->folio conversions in this path, and some of the few
> remaining users of read_cache_page() / read_mapping_page().
> 
> If anyone's concerned about all the extra lines in the diffstat, it's
> documentation that I've added.
> 
> [...]

Applied to the vfs-6.16.misc branch of the vfs/vfs.git tree.
Patches in the vfs-6.16.misc branch should appear in linux-next soon.

Please report any outstanding bugs that were missed during review in a
new review to the original patch series allowing us to drop it.

It's encouraged to provide Acked-bys and Reviewed-bys even though the
patch has now been applied. If possible patch trailers will be updated.

Note that commit hashes shown below are subject to change due to rebase,
trailer updates or similar. If in doubt, please check the listed branch.

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git
branch: vfs-6.16.misc

[1/3] fs: Convert __page_get_link() to use a folio
      https://git.kernel.org/vfs/vfs/c/5f152cc012f4
[2/3] nfs: Use a folio in nfs_get_link()
      https://git.kernel.org/vfs/vfs/c/cc8e87f312e0
[3/3] fs: Pass a folio to page_put_link()
      https://git.kernel.org/vfs/vfs/c/4ec373b74e96

Re: [PATCH 2/3] nfs: Use a folio in nfs_get_link()

[Anna Schumaker]

On 5/14/25 1:13 PM, Matthew Wilcox (Oracle) wrote:
> Mirror the changes to __page_get_link() by retrieving a folio from
> the page cache instead of a page.  Removes two hidden calls to
> compound_head().
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>

Acked-by: Anna Schumaker <anna.schumaker@oracle.com>

> ---
>  fs/nfs/symlink.c | 20 ++++++++++----------
>  1 file changed, 10 insertions(+), 10 deletions(-)
> 
> diff --git a/fs/nfs/symlink.c b/fs/nfs/symlink.c
> index 1c62a5a9f51d..004a8f6c568e 100644
> --- a/fs/nfs/symlink.c
> +++ b/fs/nfs/symlink.c
> @@ -40,31 +40,31 @@ static const char *nfs_get_link(struct dentry *dentry,
>  				struct inode *inode,
>  				struct delayed_call *done)
>  {
> -	struct page *page;
> +	struct folio *folio;
>  	void *err;
>  
>  	if (!dentry) {
>  		err = ERR_PTR(nfs_revalidate_mapping_rcu(inode));
>  		if (err)
>  			return err;
> -		page = find_get_page(inode->i_mapping, 0);
> -		if (!page)
> +		folio = filemap_get_folio(inode->i_mapping, 0);
> +		if (IS_ERR(folio))
>  			return ERR_PTR(-ECHILD);
> -		if (!PageUptodate(page)) {
> -			put_page(page);
> +		if (!folio_test_uptodate(folio)) {
> +			folio_put(folio);
>  			return ERR_PTR(-ECHILD);
>  		}
>  	} else {
>  		err = ERR_PTR(nfs_revalidate_mapping(inode, inode->i_mapping));
>  		if (err)
>  			return err;
> -		page = read_cache_page(&inode->i_data, 0, nfs_symlink_filler,
> +		folio = read_cache_folio(&inode->i_data, 0, nfs_symlink_filler,
>  				NULL);
> -		if (IS_ERR(page))
> -			return ERR_CAST(page);
> +		if (IS_ERR(folio))
> +			return ERR_CAST(folio);
>  	}
> -	set_delayed_call(done, page_put_link, page);
> -	return page_address(page);
> +	set_delayed_call(done, page_put_link, &folio->page);
> +	return folio_address(folio);
>  }
>  
>  /*