add releasepage hooks to block devices which can be used by file systems

Implement blkdev_releasepage() to release the buffer_heads and pages
after we release private data belonging to a mounted filesystem.

Cc: Toshiyuki Okajima <toshi.okajima@jp.fujitsu.com>
Cc: linux-fsdevel@vger.kernel.org
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 15 insertions, 0 deletions

diff --git a/fs/block_dev.c b/fs/block_dev.c
index 349a26c10001..1dd07e66e98a 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -1220,6 +1220,20 @@ static long block_ioctl(struct file *file, unsigned cmd, unsigned long arg)
         return blkdev_ioctl(bdev, mode, cmd, arg);
 }
 
+/*
+ * Try to release a page associated with block device when the system
+ * is under memory pressure.
+ */
+static int blkdev_releasepage(struct page *page, gfp_t wait)
+{
+        struct super_block *super = BDEV_I(page->mapping->host)->bdev.bd_super;
+
+        if (super && super->s_op->bdev_try_to_free_page)
+                return super->s_op->bdev_try_to_free_page(super, page, wait);
+
+        return try_to_free_buffers(page);
+}
+
 static const struct address_space_operations def_blk_aops = {
         .readpage       = blkdev_readpage,
         .writepage      = blkdev_writepage,
@@ -1227,6 +1241,7 @@ static const struct address_space_operations def_blk_aops = {
         .write_begin    = blkdev_write_begin,
         .write_end      = blkdev_write_end,
         .writepages     = generic_writepages,
+        .releasepage    = blkdev_releasepage,
         .direct_IO      = blkdev_direct_IO,
 };