lkml.org 
[lkml]   [2012]   [Feb]   [14]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [RFC] [PATCH v5 0/3] fadvise: support POSIX_FADV_NOREUSE
On Tue, Feb 14, 2012 at 01:33:37PM -0800, Andrew Morton wrote:
> On Sun, 12 Feb 2012 01:21:35 +0100
> Andrea Righi <andrea@betterlinux.com> wrote:
>
> > The new proposal is to implement POSIX_FADV_NOREUSE as a way to perform a real
> > drop-behind policy where applications can mark certain intervals of a file as
> > FADV_NOREUSE before accessing the data.
>
> I think you and John need to talk to each other, please. The amount of
> duplication here is extraordinary.

Yes, definitely. I'm currently reviewing and testing the John's patch
set. I was even considering to apply my patch set on top of the John's
patch, or at least propose my tree-based approach to manage the list of
the POSIX_FADV_VOLATILE ranges.

>
> Both patchsets add fields to the address_space (and hence inode), which
> is significant - we should convince ourselves that we're getting really
> good returns from a feature which does this.
>
>
>
> Regarding the use of fadvise(): I suppose it's a reasonable thing to do
> in the long term - if the feature works well, popular data streaming
> applications will eventually switch over. But I do think we should
> explore interfaces which don't require modification of userspace source
> code. Because there will always be unconverted applications, and the
> feature becomes available immediately.
>
> One such interface would be to toss the offending application into a
> container which has a modified drop-behind policy. And here we need to
> drag out the crystal ball: what *is* the best way of tuning application
> pagecache behaviour? Will we gravitate towards containerization, or
> will we gravitate towards finer-tuned fadvise/sync_page_range/etc
> behaviour? Thus far it has been the latter, and I don't think that has
> been a great success.
>
> Finally, are the problems which prompted these patchsets already
> solved? What happens if you take the offending streaming application
> and toss it into a 16MB memcg? That *should* avoid perturbing other
> things running on that machine.

Moving the streaming application into a 16MB memcg can be dangerous in
some cases... the application might start to do "bad" things, like
swapping (if the memcg can swap) or just fail due to OOMs.

>
> 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.

Thanks for your comments, Andrew.

-Andrea


\
 
 \ /
  Last update: 2012-02-15 00:01    [W:0.165 / U:0.116 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site