[v7,2/8] btrfs: don't kmap() pages from block devices
diff mbox series

Message ID 20200212071704.17505-3-johannes.thumshirn@wdc.com
State New
Headers show
Series
  • btrfs: remove buffer heads form superblock handling
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Commit Message

Johannes Thumshirn Feb. 12, 2020, 7:16 a.m. UTC
Block device mappings are never in highmem so kmap() / kunmap() calls for
pages from block devices are unneeded. Use page_address() instead of
kmap() to get to the virtual addreses.

While we're at it, read_cache_page_gfp() doesn't return NULL on error,
only an ERR_PTR, so use IS_ERR() to check for errors.

Suggested-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
---
 fs/btrfs/volumes.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

Comments

Christoph Hellwig Feb. 12, 2020, 7:25 a.m. UTC | #1
On Wed, Feb 12, 2020 at 04:16:58PM +0900, Johannes Thumshirn wrote:
> Block device mappings are never in highmem so kmap() / kunmap() calls for
> pages from block devices are unneeded. Use page_address() instead of
> kmap() to get to the virtual addreses.
> 
> While we're at it, read_cache_page_gfp() doesn't return NULL on error,
> only an ERR_PTR, so use IS_ERR() to check for errors.
> 
> Suggested-by: Christoph Hellwig <hch@lst.de>
> Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>

Looks good,

Reviewed-by: Christoph Hellwig <hch@lst.de>

Patch
diff mbox series

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 6ebdd95b798d..620794f1ea64 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -1249,7 +1249,6 @@  int btrfs_open_devices(struct btrfs_fs_devices *fs_devices,
 
 void btrfs_release_disk_super(struct page *page)
 {
-	kunmap(page);
 	put_page(page);
 }
 
@@ -1277,10 +1276,10 @@  static int btrfs_read_disk_super(struct block_device *bdev, u64 bytenr,
 	*page = read_cache_page_gfp(bdev->bd_inode->i_mapping,
 				   index, GFP_KERNEL);
 
-	if (IS_ERR_OR_NULL(*page))
+	if (IS_ERR(*page))
 		return 1;
 
-	p = kmap(*page);
+	p = page_address(*page);
 
 	/* align our pointer to the offset of the super block */
 	*disk_super = p + offset_in_page(bytenr);