• Tejun Heo's avatar
    writeback: implement memcg writeback domain based throttling · c2aa723a
    Tejun Heo authored
    
    
    While cgroup writeback support now connects memcg and blkcg so that
    writeback IOs are properly attributed and controlled, the IO back
    pressure propagation mechanism implemented in balance_dirty_pages()
    and its subroutines wasn't aware of cgroup writeback.
    
    Processes belonging to a memcg may have access to only subset of total
    memory available in the system and not factoring this into dirty
    throttling rendered it completely ineffective for processes under
    memcg limits and memcg ended up building a separate ad-hoc degenerate
    mechanism directly into vmscan code to limit page dirtying.
    
    The previous patches updated balance_dirty_pages() and its subroutines
    so that they can deal with multiple wb_domain's (writeback domains)
    and defined per-memcg wb_domain.  Processes belonging to a non-root
    memcg are bound to two wb_domains, global wb_domain and memcg
    wb_domain, and should be throttled according to IO pressures from both
    domains.  This patch updates dirty throttling code so that it repeats
    similar calculations for the two domains - the differences between the
    two are few and minor - and applies the lower of the two sets of
    resulting constraints.
    
    wb_over_bg_thresh(), which controls when background writeback
    terminates, is also updated to consider both global and memcg
    wb_domains.  It returns true if dirty is over bg_thresh for either
    domain.
    
    This makes the dirty throttling mechanism operational for memcg
    domains including writeback-bandwidth-proportional dirty page
    distribution inside them but the ad-hoc memcg throttling mechanism in
    vmscan is still in place.  The next patch will rip it out.
    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>
    c2aa723a
memcontrol.c 153 KB