• Tejun Heo's avatar
    writeback: make backing_dev_info host cgroup-specific bdi_writebacks · 52ebea74
    Tejun Heo authored
    
    
    For the planned cgroup writeback support, on each bdi
    (backing_dev_info), each memcg will be served by a separate wb
    (bdi_writeback).  This patch updates bdi so that a bdi can host
    multiple wbs (bdi_writebacks).
    
    On the default hierarchy, blkcg implicitly enables memcg.  This allows
    using memcg's page ownership for attributing writeback IOs, and every
    memcg - blkcg combination can be served by its own wb by assigning a
    dedicated wb to each memcg.  This means that there may be multiple
    wb's of a bdi mapped to the same blkcg.  As congested state is per
    blkcg - bdi combination, those wb's should share the same congested
    state.  This is achieved by tracking congested state via
    bdi_writeback_congested structs which are keyed by blkcg.
    
    bdi->wb remains unchanged and will keep serving the root cgroup.
    cgwb's (cgroup wb's) for non-root cgroups are created on-demand or
    looked up while dirtying an inode according to the memcg of the page
    being dirtied or current task.  Each cgwb is indexed on bdi->cgwb_tree
    by its memcg id.  Once an inode is associated with its wb, it can be
    retrieved using inode_to_wb().
    
    Currently, none of the filesystems has FS_CGROUP_WRITEBACK and all
    pages will keep being associated with bdi->wb.
    
    v3: inode_attach_wb() in account_page_dirtied() moved inside
        mapping_cap_account_dirty() block where it's known to be !NULL.
        Also, an unnecessary NULL check before kfree() removed.  Both
        detected by the kbuild bot.
    
    v2: Updated so that wb association is per inode and wb is per memcg
        rather than blkcg.
    Signed-off-by: default avatarTejun Heo <tj@kernel.org>
    Cc: kbuild test robot <fengguang.wu@intel.com>
    Cc: Dan Carpenter <dan.carpenter@oracle.com>
    Cc: Jens Axboe <axboe@kernel.dk>
    Cc: Jan Kara <jack@suse.cz>
    Signed-off-by: default avatarJens Axboe <axboe@fb.com>
    52ebea74
blk-cgroup.h 17.1 KB