Re: [PATCH 01/23] btrfs: pass a flags argument to cow_file_range

Re: [PATCH 01/23] btrfs: pass a flags argument to cow_file_range

[Naohiro Aota]

Christoph Hellwig <hch@lst.de> writes:

> The int used as bool unlock is not a very good way to describe the
> behavior, and the next patch will have to add another beahvior modifier.
> Switch to pass a flag instead, with an inital CFR_KEEP_LOCKED flag that
> specifies the pages should always be kept locked.  This is the inverse
> of the old unlock argument for the reason that it requires a flag for
> the exceptional behavior.

Yeah, I always struggled to remember which is the "1" means for, lock or
unlock. So, giving it a name is really nice.

> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  fs/btrfs/inode.c | 51 ++++++++++++++++++++++--------------------------
>  1 file changed, 23 insertions(+), 28 deletions(-)
>
> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> index dbbb67293e345c..92a78940991fcb 100644
> --- a/fs/btrfs/inode.c
> +++ b/fs/btrfs/inode.c
> @@ -124,11 +124,13 @@ static struct kmem_cache *btrfs_inode_cachep;
>  
>  static int btrfs_setsize(struct inode *inode, struct iattr *attr);
>  static int btrfs_truncate(struct btrfs_inode *inode, bool skip_writeback);
> +
> +#define CFR_KEEP_LOCKED		(1 << 0)
>  static noinline int cow_file_range(struct btrfs_inode *inode,
>  				   struct page *locked_page,
>  				   u64 start, u64 end, int *page_started,
> -				   unsigned long *nr_written, int unlock,
> -				   u64 *done_offset);
> +				   unsigned long *nr_written, u64 *done_offset,
> +				   u32 flags);
>  static struct extent_map *create_io_em(struct btrfs_inode *inode, u64 start,
>  				       u64 len, u64 orig_start, u64 block_start,
>  				       u64 block_len, u64 orig_block_len,
> @@ -1148,7 +1150,7 @@ static int submit_uncompressed_range(struct btrfs_inode *inode,
>  	 * can directly submit them without interruption.
>  	 */
>  	ret = cow_file_range(inode, locked_page, start, end, &page_started,
> -			     &nr_written, 0, NULL);
> +			     &nr_written, NULL, CFR_KEEP_LOCKED);
>  	/* Inline extent inserted, page gets unlocked and everything is done */
>  	if (page_started)
>  		return 0;
> @@ -1362,25 +1364,18 @@ static u64 get_extent_allocation_hint(struct btrfs_inode *inode, u64 start,
>   * locked_page is the page that writepage had locked already.  We use
>   * it to make sure we don't do extra locks or unlocks.
>   *
> - * *page_started is set to one if we unlock locked_page and do everything
> - * required to start IO on it.  It may be clean and already done with
> - * IO when we return.
> - *
> - * When unlock == 1, we unlock the pages in successfully allocated regions.
> - * When unlock == 0, we leave them locked for writing them out.
> + * When this function fails, it unlocks all pages except @locked_page.
>   *
> - * However, we unlock all the pages except @locked_page in case of failure.
> + * When this function successfully creates an inline extent, it sets page_started
> + * to 1 and unlocks all pages including locked_page and starts I/O on them.

nit: @locked_page for the consistency.

> + * (In reality inline extents are limited to a single page, so locked_page is

Same here.

Other than that, looks good to me.

Reviewed-by: Naohiro Aota <naohiro.aota@wdc.com>

> + * the only page handled anyway).
>   *
> - * In summary, page locking state will be as follow:
> + * When this function succeed and creates a normal extent, the page locking
> + * status depends on the passed in flags:
>   *
> - * - page_started == 1 (return value)
> - *     - All the pages are unlocked. IO is started.
> - *     - Note that this can happen only on success
> - * - unlock == 1
> - *     - All the pages except @locked_page are unlocked in any case
> - * - unlock == 0
> - *     - On success, all the pages are locked for writing out them
> - *     - On failure, all the pages except @locked_page are unlocked
> + * - If CFR_KEEP_LOCKED is set, all pages are kept locked.
> + * - Else all pages except for @locked_page are unlocked.
>   *
>   * When a failure happens in the second or later iteration of the
>   * while-loop, the ordered extents created in previous iterations are kept
> @@ -1391,8 +1386,8 @@ static u64 get_extent_allocation_hint(struct btrfs_inode *inode, u64 start,
>  static noinline int cow_file_range(struct btrfs_inode *inode,
>  				   struct page *locked_page,
>  				   u64 start, u64 end, int *page_started,
> -				   unsigned long *nr_written, int unlock,
> -				   u64 *done_offset)
> +				   unsigned long *nr_written, u64 *done_offset,
> +				   u32 flags)
>  {
>  	struct btrfs_root *root = inode->root;
>  	struct btrfs_fs_info *fs_info = root->fs_info;
> @@ -1558,7 +1553,7 @@ static noinline int cow_file_range(struct btrfs_inode *inode,
>  		 * Do set the Ordered (Private2) bit so we know this page was
>  		 * properly setup for writepage.
>  		 */
> -		page_ops = unlock ? PAGE_UNLOCK : 0;
> +		page_ops = (flags & CFR_KEEP_LOCKED) ? 0 : PAGE_UNLOCK;
>  		page_ops |= PAGE_SET_ORDERED;
>  
>  		extent_clear_unlock_delalloc(inode, start, start + ram_size - 1,
> @@ -1627,10 +1622,10 @@ static noinline int cow_file_range(struct btrfs_inode *inode,
>  	 * EXTENT_DEFRAG | EXTENT_CLEAR_META_RESV are handled by the cleanup
>  	 * function.
>  	 *
> -	 * However, in case of unlock == 0, we still need to unlock the pages
> -	 * (except @locked_page) to ensure all the pages are unlocked.
> +	 * However, in case of CFR_KEEP_LOCKED, we still need to unlock the
> +	 * pages (except @locked_page) to ensure all the pages are unlocked.
>  	 */
> -	if (!unlock && orig_start < start) {
> +	if ((flags & CFR_KEEP_LOCKED) && orig_start < start) {
>  		if (!locked_page)
>  			mapping_set_error(inode->vfs_inode.i_mapping, ret);
>  		extent_clear_unlock_delalloc(inode, orig_start, start - 1,
> @@ -1836,7 +1831,7 @@ static noinline int run_delalloc_zoned(struct btrfs_inode *inode,
>  
>  	while (start <= end) {
>  		ret = cow_file_range(inode, locked_page, start, end, page_started,
> -				     nr_written, 0, &done_offset);
> +				     nr_written, &done_offset, CFR_KEEP_LOCKED);
>  		if (ret && ret != -EAGAIN)
>  			return ret;
>  
> @@ -1956,7 +1951,7 @@ static int fallback_to_cow(struct btrfs_inode *inode, struct page *locked_page,
>  	}
>  
>  	return cow_file_range(inode, locked_page, start, end, page_started,
> -			      nr_written, 1, NULL);
> +			      nr_written, NULL, 0);
>  }
>  
>  struct can_nocow_file_extent_args {
> @@ -2433,7 +2428,7 @@ int btrfs_run_delalloc_range(struct btrfs_inode *inode, struct page *locked_page
>  					 page_started, nr_written, wbc);
>  	else
>  		ret = cow_file_range(inode, locked_page, start, end,
> -				     page_started, nr_written, 1, NULL);
> +				     page_started, nr_written, NULL, 0);
>  
>  out:
>  	ASSERT(ret <= 0);
> -- 
> 2.39.2

Re: [PATCH 01/23] btrfs: pass a flags argument to cow_file_range

[Christoph Hellwig]

On Thu, Jul 20, 2023 at 01:22:36PM +0200, David Sterba wrote:
> On Wed, Jun 28, 2023 at 05:31:22PM +0200, Christoph Hellwig wrote:
> > The int used as bool unlock is not a very good way to describe the
> > behavior, and the next patch will have to add another beahvior modifier.
> > Switch to pass a flag instead, with an inital CFR_KEEP_LOCKED flag that
> > specifies the pages should always be kept locked.  This is the inverse
> > of the old unlock argument for the reason that it requires a flag for
> > the exceptional behavior.
> 
> Int is the wrong type but I'm not sure that for two flags we should use
> a bit flags. Two bool parameters are IMHO fine and "CFR" does not mean
> anything, it's really only relevant for the function.

CFR stands for cow_file_range.  The good news is that with my
(huge) stack of pending pages both flags will eventually go away.
The bad news is that for an intermediate change I actually need a third
one.

Re: [PATCH 01/23] btrfs: pass a flags argument to cow_file_range

[David Sterba]

On Wed, Jun 28, 2023 at 05:31:22PM +0200, Christoph Hellwig wrote:
> The int used as bool unlock is not a very good way to describe the
> behavior, and the next patch will have to add another beahvior modifier.
> Switch to pass a flag instead, with an inital CFR_KEEP_LOCKED flag that
> specifies the pages should always be kept locked.  This is the inverse
> of the old unlock argument for the reason that it requires a flag for
> the exceptional behavior.

Int is the wrong type but I'm not sure that for two flags we should use
a bit flags. Two bool parameters are IMHO fine and "CFR" does not mean
anything, it's really only relevant for the function.

Re: [PATCH 01/23] btrfs: pass a flags argument to cow_file_range

[Johannes Thumshirn]

Looks good,
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>

[PATCH 01/23] btrfs: pass a flags argument to cow_file_range

[Christoph Hellwig]

The int used as bool unlock is not a very good way to describe the
behavior, and the next patch will have to add another beahvior modifier.
Switch to pass a flag instead, with an inital CFR_KEEP_LOCKED flag that
specifies the pages should always be kept locked.  This is the inverse
of the old unlock argument for the reason that it requires a flag for
the exceptional behavior.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 fs/btrfs/inode.c | 51 ++++++++++++++++++++++--------------------------
 1 file changed, 23 insertions(+), 28 deletions(-)

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index dbbb67293e345c..92a78940991fcb 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -124,11 +124,13 @@ static struct kmem_cache *btrfs_inode_cachep;
 
 static int btrfs_setsize(struct inode *inode, struct iattr *attr);
 static int btrfs_truncate(struct btrfs_inode *inode, bool skip_writeback);
+
+#define CFR_KEEP_LOCKED		(1 << 0)
 static noinline int cow_file_range(struct btrfs_inode *inode,
 				   struct page *locked_page,
 				   u64 start, u64 end, int *page_started,
-				   unsigned long *nr_written, int unlock,
-				   u64 *done_offset);
+				   unsigned long *nr_written, u64 *done_offset,
+				   u32 flags);
 static struct extent_map *create_io_em(struct btrfs_inode *inode, u64 start,
 				       u64 len, u64 orig_start, u64 block_start,
 				       u64 block_len, u64 orig_block_len,
@@ -1148,7 +1150,7 @@ static int submit_uncompressed_range(struct btrfs_inode *inode,
 	 * can directly submit them without interruption.
 	 */
 	ret = cow_file_range(inode, locked_page, start, end, &page_started,
-			     &nr_written, 0, NULL);
+			     &nr_written, NULL, CFR_KEEP_LOCKED);
 	/* Inline extent inserted, page gets unlocked and everything is done */
 	if (page_started)
 		return 0;
@@ -1362,25 +1364,18 @@ static u64 get_extent_allocation_hint(struct btrfs_inode *inode, u64 start,
  * locked_page is the page that writepage had locked already.  We use
  * it to make sure we don't do extra locks or unlocks.
  *
- * *page_started is set to one if we unlock locked_page and do everything
- * required to start IO on it.  It may be clean and already done with
- * IO when we return.
- *
- * When unlock == 1, we unlock the pages in successfully allocated regions.
- * When unlock == 0, we leave them locked for writing them out.
+ * When this function fails, it unlocks all pages except @locked_page.
  *
- * However, we unlock all the pages except @locked_page in case of failure.
+ * When this function successfully creates an inline extent, it sets page_started
+ * to 1 and unlocks all pages including locked_page and starts I/O on them.
+ * (In reality inline extents are limited to a single page, so locked_page is
+ * the only page handled anyway).
  *
- * In summary, page locking state will be as follow:
+ * When this function succeed and creates a normal extent, the page locking
+ * status depends on the passed in flags:
  *
- * - page_started == 1 (return value)
- *     - All the pages are unlocked. IO is started.
- *     - Note that this can happen only on success
- * - unlock == 1
- *     - All the pages except @locked_page are unlocked in any case
- * - unlock == 0
- *     - On success, all the pages are locked for writing out them
- *     - On failure, all the pages except @locked_page are unlocked
+ * - If CFR_KEEP_LOCKED is set, all pages are kept locked.
+ * - Else all pages except for @locked_page are unlocked.
  *
  * When a failure happens in the second or later iteration of the
  * while-loop, the ordered extents created in previous iterations are kept
@@ -1391,8 +1386,8 @@ static u64 get_extent_allocation_hint(struct btrfs_inode *inode, u64 start,
 static noinline int cow_file_range(struct btrfs_inode *inode,
 				   struct page *locked_page,
 				   u64 start, u64 end, int *page_started,
-				   unsigned long *nr_written, int unlock,
-				   u64 *done_offset)
+				   unsigned long *nr_written, u64 *done_offset,
+				   u32 flags)
 {
 	struct btrfs_root *root = inode->root;
 	struct btrfs_fs_info *fs_info = root->fs_info;
@@ -1558,7 +1553,7 @@ static noinline int cow_file_range(struct btrfs_inode *inode,
 		 * Do set the Ordered (Private2) bit so we know this page was
 		 * properly setup for writepage.
 		 */
-		page_ops = unlock ? PAGE_UNLOCK : 0;
+		page_ops = (flags & CFR_KEEP_LOCKED) ? 0 : PAGE_UNLOCK;
 		page_ops |= PAGE_SET_ORDERED;
 
 		extent_clear_unlock_delalloc(inode, start, start + ram_size - 1,
@@ -1627,10 +1622,10 @@ static noinline int cow_file_range(struct btrfs_inode *inode,
 	 * EXTENT_DEFRAG | EXTENT_CLEAR_META_RESV are handled by the cleanup
 	 * function.
 	 *
-	 * However, in case of unlock == 0, we still need to unlock the pages
-	 * (except @locked_page) to ensure all the pages are unlocked.
+	 * However, in case of CFR_KEEP_LOCKED, we still need to unlock the
+	 * pages (except @locked_page) to ensure all the pages are unlocked.
 	 */
-	if (!unlock && orig_start < start) {
+	if ((flags & CFR_KEEP_LOCKED) && orig_start < start) {
 		if (!locked_page)
 			mapping_set_error(inode->vfs_inode.i_mapping, ret);
 		extent_clear_unlock_delalloc(inode, orig_start, start - 1,
@@ -1836,7 +1831,7 @@ static noinline int run_delalloc_zoned(struct btrfs_inode *inode,
 
 	while (start <= end) {
 		ret = cow_file_range(inode, locked_page, start, end, page_started,
-				     nr_written, 0, &done_offset);
+				     nr_written, &done_offset, CFR_KEEP_LOCKED);
 		if (ret && ret != -EAGAIN)
 			return ret;
 
@@ -1956,7 +1951,7 @@ static int fallback_to_cow(struct btrfs_inode *inode, struct page *locked_page,
 	}
 
 	return cow_file_range(inode, locked_page, start, end, page_started,
-			      nr_written, 1, NULL);
+			      nr_written, NULL, 0);
 }
 
 struct can_nocow_file_extent_args {
@@ -2433,7 +2428,7 @@ int btrfs_run_delalloc_range(struct btrfs_inode *inode, struct page *locked_page
 					 page_started, nr_written, wbc);
 	else
 		ret = cow_file_range(inode, locked_page, start, end,
-				     page_started, nr_written, 1, NULL);
+				     page_started, nr_written, NULL, 0);
 
 out:
 	ASSERT(ret <= 0);
-- 
2.39.2