LP# 440522: FSCACHE modules not compiled in

Tim Gardner tim.gardner at canonical.com
Wed Mar 10 17:52:05 UTC 2010

On 03/09/2010 01:14 PM, Christian Kujau wrote:
> On Tue, 9 Mar 2010 at 06:56, Tim Gardner wrote:
>> The issue with NFS_FSCACHE in particular is that upstream support appears to
>> be lukewarm, e.g., neither fscache.c or fscache-index.c has been touched since
>> April 2009,
> According to git-log, fs/nfs/fscache.c, has been touched in Sep 2009, Nov
> 2009 and now in March again. fs/fscache has been touched in Nov 2009, the
> same goes for fs/cachefiles.

You are correct. Not sure how I missed that.

>> yet the feature is still marked EXPERIMENTAL.
> As stated in the bugreport this flag has been removed upstream now, for
> 2.6.34. However, as pointed out in the report and in [0] too, the
> EXPERIMENTAL flag is not considered useful any more by many upstream
> developers.

Activity in the 2.6.34 kernel isn't relevant to the code base we have in 

> Furthermore, Ubuntu has enabled other EXPERIMENTAL features (e.g.
> CONFIG_FSCACHE, which only recently had its EXPERIMENTAL flag removed).
>> Furthermore, NFS_FSCACHE cannot be built as a module
> Indeed, the bug description should be changed :-)
>> i.e., enabling this feature is going to affect the base NFS implementation.
>> Until this situation changes, I'm not going into a long term release with
>> an experimental feature in the mainline NFS path.
> OpenSuse does it (since at least May 2005), Fedora does it too[1]. Again,
> I agree with Arjan[0] here: it's not EXPERIMENTAL just because someone
> tagged it so. If not enabled, nothing changes from a user's perspective.
> If bugs are found (with caching enabled or not), they're likely NOT to
> occur only on Ubuntu machines but will have to be addressed upstream.
> Please reconsider.
> Thanks,
> Christian.
> [0] http://marc.info/?l=linux-nfs&m=126684776217594&w=2
> [1] http://lwn.net/Articles/160122/

At this late stage in the development process (kernel freeze was 
effectively yesterday) it just ain't gonna happen. We _might_ consider 
an SRU after Lucid has been released, but only if there is compelling 
evidence that NFS caching does not affect stability (i.e., no 
regressions), and that it provides a real benefit.

Your best bet is to ensure this feature is enabled for L+1.

Tim Gardner tim.gardner at canonical.com

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