Re: [RFC] [PATCH v5 0/3] fadvise: support POSIX_FADV_NOREUSE

On Thu, Feb 16, 2012 at 08:48:31AM +0900, KAMEZAWA Hiroyuki wrote:

On Wed, 15 Feb 2012 02:35:24 +0100
Andrea Righi [off-list ref] wrote:

quoted

On Tue, Feb 14, 2012 at 03:22:20PM -0800, Andrew Morton wrote:

quoted

On Tue, 14 Feb 2012 23:59:22 +0100
Andrea Righi [off-list ref] wrote:

quoted

On Tue, Feb 14, 2012 at 01:33:37PM -0800, Andrew Morton wrote:

quoted

On Sun, 12 Feb 2012 01:21:35 +0100
Andrea Righi [off-list ref] wrote: 
And yes, a container-based approach is pretty crude, and one can
envision applications which only want modified reclaim policy for one
particualr file.  But I suspect an application-wide reclaim policy
solves 90% of the problems.

I really like the container-based approach. But for this we need a
better file cache control in the memory cgroup; now we have the
accounting of file pages, but there's no way to limit them.

Again, if/whem memcg becomes sufficiently useful for this application
we're left maintaining the obsolete POSIX_FADVISE_NOREUSE for ever.

Yes, totally agree. For the future a memcg-based solution is probably
the best way to go.

This reminds me to the old per-memcg dirty memory discussion
(http://thread.gmane.org/gmane.linux.kernel.mm/67114), cc'ing Greg.

Maybe the generic feature to provide that could solve both problems is
a better file cache isolation in memcg.

Can you think of example interface for us ?
I'd like to discuss this in mm-summit if we have a chance.

Thanks,
-Kame

Sure! I'll try to write down more detailed ideas.

For now the best interface that I can see is to add something like
memory.file.* in cgroupfs.

The NOREUSE-like policy that I was trying to implement via fadvise() can
be probably implemented by setting memory.file.limit_in_bytes=0 (or
using a very small value).

A cgroup like this could use any amount of memory (according to the
other memory.* settings), but it should drop any file cache page as soon
as possible, if the page was not present in memory before. IOW, this
cgroup shouldn't disturb the state of the page cache for the other
cgroups.

Another interesting usage is to provide different levels of service. For
example, using different values for memory.file.limit_in_byte would make
possible to specify that file cache pages of certain cgroups are
reclaimed before others. This would be a very nice feature IMHO, also
for those who want to provide different levels of service per-user.

Thoughts?

Thanks,
-Andrea

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