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

From: Jan Kara
Date: Wed Feb 11 2015 - 02:32:39 EST

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.

Jan Kara <jack@xxxxxxx>
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