* [PATCH][RFC] NFS: Adding hooks to enable the use of FS-Cache
@ 2006-04-21 15:14 Steve Dickson
2006-04-21 15:31 ` Trond Myklebust
0 siblings, 1 reply; 6+ messages in thread
From: Steve Dickson @ 2006-04-21 15:14 UTC (permalink / raw)
To: Trond Myklebust; +Cc: Andrew Morton, linux-fsdevel, linux-cachefs
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This patch (based on Trond's nfs-2.6 git tree) adds the hooks need to
allow NFS to use the generic filesystem caching facility FS-Cache.
Caching is done on a per mount bases. To activate caching, the 'fsc'
flag is need as a mount option.
Ex:
mount -o fsc server:/export /mnt
(binary and source rpms as well as the actual patch are available at
http://people.redhat.com/steved/cachefs/util-linux/)
NFS uses the cache on a readonly bases; Meaning only reads are caches
not writes. But this *does not* mean filesystems have to be mounted
read only. Filesystems are mounted read/write but only data from
reads will be cached. When a file is opened with either RW or WR
bits, the caching will be turned off (see nfs_open for the details).
The reason for read only is became quite apparent that keeping the cache
coherent while jugging both reads and writes is pretty hard. So it was
decided to start with a read only implementation and then move on to a
read/write implementation in the future...
There are still a few rough spots in this patch. One being the
sysctl variables that show what, if any, caching is being done need
to be rolled into NFS I/O metrics code that recently went in.
The second one being, what David termed as, NFS aliasing. The way
NFS manages its super blocks would cause double caching since the
cookies returned by the cache would not be unique. We got around
this problem by making each nfs mount have unique 'fsctag' which
would be used to generate the caching cookie. The default fsctag
value is the mount point but it also can be set on the command line
(which is undocumented at this point since its not clear we really
want to do this).
Unfortunately having the mount command passed the kernel a string turned
out to a bit difficult since NFS used a binary interface (something
that will hopefully change this summer). So David came up with the idea
(not too surprising) of using the keyrings to passed down the string
which did work very well... But as I said, we have every intending of
change the binary interface into an ascii one and when that happens,
this interface will change.
Finally there still needs to be some work on mmapped pages. Its not
clear NFS is used the cache as well as it could when pages are mmapped.
I'm still investigating...
Now I'm sure Trond will find several more rough spots... ;-) but
these are all of the ones I know about....
steved.
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^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH][RFC] NFS: Adding hooks to enable the use of FS-Cache
2006-04-21 15:14 [PATCH][RFC] NFS: Adding hooks to enable the use of FS-Cache Steve Dickson
@ 2006-04-21 15:31 ` Trond Myklebust
2006-04-21 15:42 ` Steve Dickson
2006-04-21 15:44 ` [Linux-cachefs] " David Howells
0 siblings, 2 replies; 6+ messages in thread
From: Trond Myklebust @ 2006-04-21 15:31 UTC (permalink / raw)
To: Steve Dickson; +Cc: Andrew Morton, linux-fsdevel, linux-cachefs
On Fri, 2006-04-21 at 11:14 -0400, Steve Dickson wrote:
> This patch (based on Trond's nfs-2.6 git tree) adds the hooks need to
> allow NFS to use the generic filesystem caching facility FS-Cache.
> Caching is done on a per mount bases. To activate caching, the 'fsc'
> flag is need as a mount option.
> Ex:
> mount -o fsc server:/export /mnt
>
> (binary and source rpms as well as the actual patch are available at
> http://people.redhat.com/steved/cachefs/util-linux/)
Hmm... Are you sure that is based on the latest trees? AFAICS it
shouldn't even apply to stock 2.6.17-rc2 since it doesn't take into
account the fact that we already use PagePrivate()+nfs_invalidatepage in
order to fix truncate races.
Could you look into that please?
Cheers,
Trond
> NFS uses the cache on a readonly bases; Meaning only reads are caches
> not writes. But this *does not* mean filesystems have to be mounted
> read only. Filesystems are mounted read/write but only data from
> reads will be cached. When a file is opened with either RW or WR
> bits, the caching will be turned off (see nfs_open for the details).
> The reason for read only is became quite apparent that keeping the cache
> coherent while jugging both reads and writes is pretty hard. So it was
> decided to start with a read only implementation and then move on to a
> read/write implementation in the future...
>
> There are still a few rough spots in this patch. One being the
> sysctl variables that show what, if any, caching is being done need
> to be rolled into NFS I/O metrics code that recently went in.
>
> The second one being, what David termed as, NFS aliasing. The way
> NFS manages its super blocks would cause double caching since the
> cookies returned by the cache would not be unique. We got around
> this problem by making each nfs mount have unique 'fsctag' which
> would be used to generate the caching cookie. The default fsctag
> value is the mount point but it also can be set on the command line
> (which is undocumented at this point since its not clear we really
> want to do this).
>
> Unfortunately having the mount command passed the kernel a string turned
> out to a bit difficult since NFS used a binary interface (something
> that will hopefully change this summer). So David came up with the idea
> (not too surprising) of using the keyrings to passed down the string
> which did work very well... But as I said, we have every intending of
> change the binary interface into an ascii one and when that happens,
> this interface will change.
>
> Finally there still needs to be some work on mmapped pages. Its not
> clear NFS is used the cache as well as it could when pages are mmapped.
> I'm still investigating...
>
> Now I'm sure Trond will find several more rough spots... ;-) but
> these are all of the ones I know about....
>
> steved.
>
>
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH][RFC] NFS: Adding hooks to enable the use of FS-Cache
2006-04-21 15:31 ` Trond Myklebust
@ 2006-04-21 15:42 ` Steve Dickson
2006-04-21 15:53 ` Trond Myklebust
2006-04-21 15:44 ` [Linux-cachefs] " David Howells
1 sibling, 1 reply; 6+ messages in thread
From: Steve Dickson @ 2006-04-21 15:42 UTC (permalink / raw)
To: Trond Myklebust; +Cc: Andrew Morton, linux-fsdevel, linux-cachefs
Trond Myklebust wrote:
> On Fri, 2006-04-21 at 11:14 -0400, Steve Dickson wrote:
>
>>This patch (based on Trond's nfs-2.6 git tree) adds the hooks need to
>>allow NFS to use the generic filesystem caching facility FS-Cache.
>>Caching is done on a per mount bases. To activate caching, the 'fsc'
>>flag is need as a mount option.
>>Ex:
>> mount -o fsc server:/export /mnt
>>
>>(binary and source rpms as well as the actual patch are available at
>> http://people.redhat.com/steved/cachefs/util-linux/)
>
>
> Hmm... Are you sure that is based on the latest trees?
Just this morning I did an git fetch on my cloned nfs-2.6
tree... and everything seem to apply just fine...
> AFAICS it shouldn't even apply to stock 2.6.17-rc2 since it doesn't take into
> account the fact that we already use PagePrivate()+nfs_invalidatepage in
> order to fix truncate races.
hmm... I did not see that... so there must a disconnect somewhere...
> Could you look into that please?
Will do...
steved.
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [Linux-cachefs] Re: [PATCH][RFC] NFS: Adding hooks to enable the use of FS-Cache
2006-04-21 15:31 ` Trond Myklebust
2006-04-21 15:42 ` Steve Dickson
@ 2006-04-21 15:44 ` David Howells
1 sibling, 0 replies; 6+ messages in thread
From: David Howells @ 2006-04-21 15:44 UTC (permalink / raw)
To: Linux filesystem caching discussion list
Cc: Trond Myklebust, Andrew Morton, linux-fsdevel
Steve Dickson <SteveD@redhat.com> wrote:
> > Hmm... Are you sure that is based on the latest trees?
> Just this morning I did an git fetch on my cloned nfs-2.6
> tree... and everything seem to apply just fine...
Well... if Steve's using my NFS patch, then it overrides the usage of
PG_private to deal with truncate madness. This also needs fixing.
David
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH][RFC] NFS: Adding hooks to enable the use of FS-Cache
2006-04-21 15:42 ` Steve Dickson
@ 2006-04-21 15:53 ` Trond Myklebust
2006-04-21 15:56 ` Steve Dickson
0 siblings, 1 reply; 6+ messages in thread
From: Trond Myklebust @ 2006-04-21 15:53 UTC (permalink / raw)
To: Steve Dickson; +Cc: Andrew Morton, linux-fsdevel, linux-cachefs
On Fri, 2006-04-21 at 11:42 -0400, Steve Dickson wrote:
> Trond Myklebust wrote:
> > On Fri, 2006-04-21 at 11:14 -0400, Steve Dickson wrote:
> >
> >>This patch (based on Trond's nfs-2.6 git tree) adds the hooks need to
> >>allow NFS to use the generic filesystem caching facility FS-Cache.
> >>Caching is done on a per mount bases. To activate caching, the 'fsc'
> >>flag is need as a mount option.
> >>Ex:
> >> mount -o fsc server:/export /mnt
> >>
> >>(binary and source rpms as well as the actual patch are available at
> >> http://people.redhat.com/steved/cachefs/util-linux/)
> >
> >
> > Hmm... Are you sure that is based on the latest trees?
> Just this morning I did an git fetch on my cloned nfs-2.6
> tree... and everything seem to apply just fine...
'git fetch' or 'git pull'? You almost always want to do the latter,
since the former doesn't attempt to merge the changes into your
repository.
Cheers,
Trond
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH][RFC] NFS: Adding hooks to enable the use of FS-Cache
2006-04-21 15:53 ` Trond Myklebust
@ 2006-04-21 15:56 ` Steve Dickson
0 siblings, 0 replies; 6+ messages in thread
From: Steve Dickson @ 2006-04-21 15:56 UTC (permalink / raw)
To: Trond Myklebust; +Cc: Andrew Morton, linux-fsdevel, linux-cachefs
Trond Myklebust wrote:
> 'git fetch' or 'git pull'? You almost always want to do the latter,
> since the former doesn't attempt to merge the changes into your
> repository.
ah... I did the former... thanks...
steved.
^ permalink raw reply [flat|nested] 6+ messages in thread
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2006-04-21 15:14 [PATCH][RFC] NFS: Adding hooks to enable the use of FS-Cache Steve Dickson
2006-04-21 15:31 ` Trond Myklebust
2006-04-21 15:42 ` Steve Dickson
2006-04-21 15:53 ` Trond Myklebust
2006-04-21 15:56 ` Steve Dickson
2006-04-21 15:44 ` [Linux-cachefs] " David Howells
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