Re: [PATCH v8 11/12] writeback: make background writeback cgroupaware

From: KAMEZAWA Hiroyuki
Date: Tue Jun 07 2011 - 05:03:43 EST

On Fri, 3 Jun 2011 09:12:17 -0700
Greg Thelen <gthelen@xxxxxxxxxx> wrote:

> When the system is under background dirty memory threshold but a cgroup
> is over its background dirty memory threshold, then only writeback
> inodes associated with the over-limit cgroup(s).
> In addition to checking if the system dirty memory usage is over the
> system background threshold, over_bground_thresh() also checks if any
> cgroups are over their respective background dirty memory thresholds.
> The writeback_control.for_cgroup field is set to distinguish between a
> system and memcg overage.
> If performing cgroup writeback, move_expired_inodes() skips inodes that
> do not contribute dirty pages to the cgroup being written back.
> After writing some pages, wb_writeback() will call
> mem_cgroup_writeback_done() to update the set of over-bg-limits memcg.
> Signed-off-by: Greg Thelen <gthelen@xxxxxxxxxx>

> ---
> Changelog since v7:
> - over_bground_thresh() now sets shared_inodes=1. In -v7 per memcg
> background writeback did not, so it did not write pages of shared
> inodes in background writeback. In the (potentially common) case
> where the system dirty memory usage is below the system background
> dirty threshold but at least one cgroup is over its background dirty
> limit, then per memcg background writeback is queued for any
> over-background-threshold cgroups. Background writeback should be
> allowed to writeback shared inodes. The hope is that writing such
> inodes has good chance of cleaning the inodes so they can transition
> from shared to non-shared. Such a transition is good because then the
> inode will remain unshared until it is written by multiple cgroup.
> Non-shared inodes offer better isolation.

If you post v9, please adds above explanation as the comments in the code.

Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>

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