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    writeback: implement foreign cgroup inode bdi_writeback switching · d10c8095
    Tejun Heo 提交于
    As concurrent write sharing of an inode is expected to be very rare
    and memcg only tracks page ownership on first-use basis severely
    confining the usefulness of such sharing, cgroup writeback tracks
    ownership per-inode.  While the support for concurrent write sharing
    of an inode is deemed unnecessary, an inode being written to by
    different cgroups at different points in time is a lot more common,
    and, more importantly, charging only by first-use can too readily lead
    to grossly incorrect behaviors (single foreign page can lead to
    gigabytes of writeback to be incorrectly attributed).
    
    To resolve this issue, cgroup writeback detects the majority dirtier
    of an inode and transfers the ownership to it.  The previous patches
    implemented the foreign condition detection mechanism and laid the
    groundwork.  This patch implements the actual switching.
    
    With the previously implemented [unlocked_]inode_to_wb_and_list_lock()
    and wb stat transaction, grabbing wb->list_lock, inode->i_lock and
    mapping->tree_lock gives us full exclusion against all wb operations
    on the target inode.  inode_switch_wb_work_fn() grabs all the locks
    and transfers the inode atomically along with its RECLAIMABLE and
    WRITEBACK stats.
    Signed-off-by: NTejun 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: NJens Axboe <axboe@fb.com>
    d10c8095
fs-writeback.c 66.8 KB