fs: kill BDI_CAP_SWAP_BACKED

This bdi flag isn't too useful - we can determine that a vma is backed by
either swap or shmem trivially in the caller.

This also allows removing the backing_dev_info instaces for swap and shmem
in favor of noop_backing_dev_info.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <axboe@fb.com>

1 files changed, 7 insertions, 18 deletions

diff --git a/mm/shmem.c b/mm/shmem.c
index 73ba1df7c8ba..1b77eaf589fd 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -191,11 +191,6 @@ static const struct inode_operations shmem_dir_inode_operations;
 static const struct inode_operations shmem_special_inode_operations;
 static const struct vm_operations_struct shmem_vm_ops;
 
-static struct backing_dev_info shmem_backing_dev_info  __read_mostly = {
-        .ra_pages       = 0,    /* No readahead */
-        .capabilities   = BDI_CAP_NO_ACCT_AND_WRITEBACK | BDI_CAP_SWAP_BACKED,
-};
-
 static LIST_HEAD(shmem_swaplist);
 static DEFINE_MUTEX(shmem_swaplist_mutex);
 
@@ -765,11 +760,11 @@ static int shmem_writepage(struct page *page, struct writeback_control *wbc)
                 goto redirty;
 
         /*
-         * shmem_backing_dev_info's capabilities prevent regular writeback or
-         * sync from ever calling shmem_writepage; but a stacking filesystem
-         * might use ->writepage of its underlying filesystem, in which case
-         * tmpfs should write out to swap only in response to memory pressure,
-         * and not for the writeback threads or sync.
+         * Our capabilities prevent regular writeback or sync from ever calling
+         * shmem_writepage; but a stacking filesystem might use ->writepage of
+         * its underlying filesystem, in which case tmpfs should write out to
+         * swap only in response to memory pressure, and not for the writeback
+         * threads or sync.
          */
         if (!wbc->for_reclaim) {
                 WARN_ON_ONCE(1);        /* Still happens? Tell us about it! */
@@ -1415,7 +1410,7 @@ static struct inode *shmem_get_inode(struct super_block *sb, const struct inode
                 inode->i_ino = get_next_ino();
                 inode_init_owner(inode, dir, mode);
                 inode->i_blocks = 0;
-                inode->i_mapping->backing_dev_info = &shmem_backing_dev_info;
+                inode->i_mapping->backing_dev_info = &noop_backing_dev_info;
                 inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
                 inode->i_generation = get_seconds();
                 info = SHMEM_I(inode);
@@ -1461,7 +1456,7 @@ static struct inode *shmem_get_inode(struct super_block *sb, const struct inode
 
 bool shmem_mapping(struct address_space *mapping)
 {
-        return mapping->backing_dev_info == &shmem_backing_dev_info;
+        return mapping->host->i_sb->s_op == &shmem_ops;
 }
 
 #ifdef CONFIG_TMPFS
@@ -3226,10 +3221,6 @@ int __init shmem_init(void)
         if (shmem_inode_cachep)
                 return 0;
 
-        error = bdi_init(&shmem_backing_dev_info);
-        if (error)
-                goto out4;
-
         error = shmem_init_inodecache();
         if (error)
                 goto out3;
@@ -3253,8 +3244,6 @@ out1:
 out2:
         shmem_destroy_inodecache();
 out3:
-        bdi_destroy(&shmem_backing_dev_info);
-out4:
         shm_mnt = ERR_PTR(error);
         return error;
 }