On Mon, 22 Feb 2010 12:58:33 -0500
Vivek Goyal <vgoyal@xxxxxxxxxx> wrote:
> On Mon, Feb 22, 2010 at 11:06:40PM +0530, Balbir Singh wrote:
> > * Vivek Goyal <vgoyal@xxxxxxxxxx> [2010-02-22 09:27:45]:
> >
> >
> > >
> > > May be we can modify writeback_inodes_wbc() to check first dirty page
> > > of the inode. And if it does not belong to same memcg as the task who
> > > is performing balance_dirty_pages(), then skip that inode.
> >
> > Do you expect all pages of an inode to be paged in by the same cgroup?
>
> I guess at least in simple cases. Not sure whether it will cover majority
> of usage or not and up to what extent that matters.
>
> If we start doing background writeout, on per page (like memory reclaim),
> the it probably will be slower and hence flusing out pages sequentially
> from inode makes sense.
>
> At one point I was thinking, like pages, can we have an inode list per
> memory cgroup so that writeback logic can traverse that inode list to
> determine which inodes need to be cleaned. But associating inodes to
> memory cgroup is not very intutive at the same time, we again have the
> issue of shared file pages from two differnent cgroups.
>
> But I guess, a simpler scheme would be to just check first dirty page from
> inode and if it does not belong to memory cgroup of task being throttled,
> skip it.
>
> It will not cover the case of shared file pages across memory cgroups, but
> at least something relatively simple to begin with. Do you have more ideas
> on how it can be handeled better.
>
If pagesa are "shared", it's hard to find _current_ owner. Then, what I'm
thinking as memcg's update is a memcg-for-page-cache and pagecache
migration between memcg.
The idea is
- At first, treat page cache as what we do now.
- When a process touches page cache, check process's memcg and page cache's
memcg. If process-memcg != pagecache-memcg, we migrate it to a special
container as memcg-for-page-cache.
Then,
- read-once page caches are handled by local memcg.
- shared page caches are handled in specail memcg for "shared".
But this will add significant overhead in native implementation.
(We may have to use page flags rather than page_cgroup's....)
I'm now wondering about
- set "shared flag" to a page_cgroup if cached pages are accessed.
- sweep them to special memcg in other (kernel) daemon when we hit thresh
or some.
But hmm, I'm not sure that memcg-for-shared-page-cache is accepptable
for anyone.
Thanks,
-Kame
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