• Tejun Heo's avatar
    writeback: make writeback_control track the inode being written back · b16b1deb
    Tejun Heo authored
    Currently, for cgroup writeback, the IO submission paths directly
    associate the bio's with the blkcg from inode_to_wb_blkcg_css();
    however, it'd be necessary to keep more writeback context to implement
    foreign inode writeback detection.  wbc (writeback_control) is the
    natural fit for the extra context - it persists throughout the
    writeback of each inode and is passed all the way down to IO
    submission paths.
    
    This patch adds wbc_attach_and_unlock_inode(), wbc_detach_inode(), and
    wbc_attach_fdatawrite_inode() which are used to associate wbc with the
    inode being written back.  IO submission paths now use wbc_init_bio()
    instead of directly associating bio's with blkcg themselves.  This
    leaves inode_to_wb_blkcg_css() w/o any user.  The function is removed.
    
    wbc currently only tracks the associated wb (bdi_writeback).  Future
    patches will add more for foreign inode detection.  The association is
    established under i_lock which will be depended upon when migrating
    foreign inodes to other wb's.
    
    As currently, once established, inode to wb association never changes,
    going through wbc when initializing bio's doesn't cause any behavior
    changes.
    
    v2: submit_blk_blkcg() now checks whether the wbc is associated with a
        wb before dereferencing it.  This can happen when pageout() is
        writing pages directly without going through the usual writeback
        path.  As pageout() path is single-threaded, we don't want it to
        be blocked behind a slow cgroup and ultimately want it to delegate
        actual writing to the usual writeback path.
    Signed-off-by: default avatarTejun Heo <tj@kernel.org>
    Cc: Jens Axboe <axboe@kernel.dk>
    Cc: Jan Kara <jack@suse.cz>
    Cc: Wu Fengguang <fengguang.wu@intel.com>
    Cc: Greg Thelen <gthelen@google.com>
    Signed-off-by: default avatarJens Axboe <axboe@fb.com>
    b16b1deb
writeback.h 11.6 KB