Re: [RFC] Making memcg track ownership per address_space or anon_vma

[Jan Kara <jack@suse.cz>]

  Hello Tejun,

On Tue 10-02-15 21:19:06, Tejun Heo wrote:
> On Sat, Feb 07, 2015 at 09:38:39AM -0500, Tejun Heo wrote:
> > If we can argue that memcg and blkcg having different views is
> > meaningful and characterize and justify the behaviors stemming from
> > the deviation, sure, that'd be fine, but I don't think we have that as
> > of now.
...
> So, based on the assumption that write sharings are mostly incidental
> and temporary (ie. we're basically declaring that we don't support
> persistent write sharing), how about something like the following?
> 
> 1. memcg contiues per-page tracking.
> 
> 2. Each inode is associated with a single blkcg at a given time and
>    written out by that blkcg.
> 
> 3. While writing back, if the number of pages from foreign memcg's is
>    higher than certain ratio of total written pages, the inode is
>    marked as disowned and the writeback instance is optionally
>    terminated early.  e.g. if the ratio of foreign pages is over 50%
>    after writing out the number of pages matching 5s worth of write
>    bandwidth for the bdi, mark the inode as disowned.
> 
> 4. On the following dirtying of the inode, the inode is associated
>    with the matching blkcg of the dirtied page.  Note that this could
>    be the next cycle as the inode could already have been marked dirty
>    by the time the above condition triggered.  In that case, the
>    following writeback would be terminated early too.
> 
> This should provide sufficient corrective pressure so that incidental
> and temporary sharing of an inode doesn't become a persistent issue
> while keeping the complexity necessary for implementing such pressure
> fairly minimal and self-contained.  Also, the changes necessary for
> individual filesystems would be minimal.
  I like this proposal. It looks simple enough and when inodes aren't
pernamently write-shared it converges to the blkcg that is currently
writing to the inode. So ack from me.

								Honza
-- 
Jan Kara <jack@suse.cz>
SUSE Labs, CR