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writeback: always use sb->s_bdi for writeback purposes 

We currently use struct backing_dev_info for various different purposes.
Originally it was introduced to describe a backing device which includes
an unplug and congestion function and various bits of readahead information
and VM-relevant flags.  We're also using for tracking dirty inodes for
writeback.

To make writeback properly find all inodes we need to only access the
per-filesystem backing_device pointed to by the superblock in ->s_bdi
inside the writeback code, and not the instances pointeded to by
inode->i_mapping->backing_dev which can be overriden by special devices
or might not be set at all by some filesystems.

Long term we should split out the writeback-relevant bits of struct
backing_device_info (which includes more than the current bdi_writeback)
and only point to it from the superblock while leaving the traditional
backing device as a separate structure that can be overriden by devices.

The one exception for now is the block device filesystem which really
wants different writeback contexts for it's different (internal) inodes
to handle the writeout more efficiently.  For now we do this with
a hack in fs-writeback.c because we're so late in the cycle, but in
the future I plan to replace this with a superblock method that allows
for multiple writeback contexts per filesystem.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
This commit is contained in:
Christoph Hellwig 2010-10-04 14:25:33 +02:00 committed by Jens Axboe
parent c6ea21e35b
commit aaead25b95
1 changed files with 4 additions and 15 deletions
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19
fs/fs-writeback.c
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@ -72,22 +72,11 @@ int writeback_in_progress(struct backing_dev_info *bdi)
static inline struct backing_dev_info *inode_to_bdi(struct inode *inode) static inline struct backing_dev_info *inode_to_bdi(struct inode *inode)
{ {
struct super_block *sb = inode->i_sb; struct super_block *sb = inode->i_sb;
struct backing_dev_info *bdi = inode->i_mapping->backing_dev_info;
/* if (strcmp(sb->s_type->name, "bdev") == 0)
* For inodes on standard filesystems, we use superblock's bdi. For return inode->i_mapping->backing_dev_info;
* inodes on virtual filesystems, we want to use inode mapping's bdi
* because they can possibly point to something useful (think about return sb->s_bdi;
* block_dev filesystem).
*/
if (sb->s_bdi && sb->s_bdi != &noop_backing_dev_info) {
/* Some device inodes could play dirty tricks. Catch them... */
WARN(bdi != sb->s_bdi && bdi_cap_writeback_dirty(bdi),
"Dirtiable inode bdi %s != sb bdi %s\n",
bdi->name, sb->s_bdi->name);
return sb->s_bdi;
}
return bdi;
} }
static void bdi_queue_work(struct backing_dev_info *bdi, static void bdi_queue_work(struct backing_dev_info *bdi,