From: David Howells <dhowells@redhat.com>
To: Martin Waitz <tali@admingilde.org>
Cc: Linux filesystem caching discussion list
<linux-cachefs@redhat.com>, Steve Dickson <SteveD@redhat.com>,
nfs@lists.sourceforge.net,
linux-kernel <linux-kernel@vger.kernel.org>,
Clemens Schwaighofer <cs@tequila.co.jp>,
Alexander Viro <aviro@redhat.com>
Subject: Re: [Linux-cachefs] Re: [PATCH] NFS using CacheFS
Date: Mon, 11 Oct 2004 16:18:37 +0100 [thread overview]
Message-ID: <10462.1097507917@redhat.com> (raw)
In-Reply-To: <20041011142329.GJ4072@admingilde.org>
> > The 'fscache' flag will be coming along with the nfs4 support, since
> > nfs4 mounting code does not have an open (unused) mounting flag....
>
> is such a flag even neccessary?
> The way I see fscache is that its operations will be no-ops anyway if you
> haven't mounted any backing cache.
There are two reasons:
(1) The fscache middle bit builds up a cookie tree even if there are no
backing caches. This means if the cache is added later (NFS root, for
example), the netfs then starts caching immediately without requiring a
remount.
(2) NFS is not currently safe with respect to fscache in the following
situation:
mount warthog:/warthog/x /x
mount warthog:/warthog /y
Because NFS ends up with two superblocks for what is one set of
filehandles. This means it tries to get the same cookies out of fscache
twice, which fscache is ill-equipped to handle.
This also introduces unnecessary (IMNSHO) aliasing in each client of
inodes and pages both.
I have a patch to fix NFS to cope with this by modifying the get_sb()
method to allow the filesystem to override the automatic selection of
super->s_root as the root dentry. However, Al Viro is leery of the patch
for some reason.
David
WARNING: multiple messages have this Message-ID (diff)
From: David Howells <dhowells@redhat.com>
To: Martin Waitz <tali@admingilde.org>
Cc: Linux filesystem caching discussion list
<linux-cachefs@redhat.com>,
nfs@lists.sourceforge.net, Alexander Viro <aviro@redhat.com>,
linux-kernel <linux-kernel@vger.kernel.org>,
Steve Dickson <SteveD@redhat.com>,
Clemens Schwaighofer <cs@tequila.co.jp>
Subject: Re: Re: [PATCH] NFS using CacheFS
Date: Mon, 11 Oct 2004 16:18:37 +0100 [thread overview]
Message-ID: <10462.1097507917@redhat.com> (raw)
In-Reply-To: <20041011142329.GJ4072@admingilde.org>
> > The 'fscache' flag will be coming along with the nfs4 support, since
> > nfs4 mounting code does not have an open (unused) mounting flag....
>
> is such a flag even neccessary?
> The way I see fscache is that its operations will be no-ops anyway if you
> haven't mounted any backing cache.
There are two reasons:
(1) The fscache middle bit builds up a cookie tree even if there are no
backing caches. This means if the cache is added later (NFS root, for
example), the netfs then starts caching immediately without requiring a
remount.
(2) NFS is not currently safe with respect to fscache in the following
situation:
mount warthog:/warthog/x /x
mount warthog:/warthog /y
Because NFS ends up with two superblocks for what is one set of
filehandles. This means it tries to get the same cookies out of fscache
twice, which fscache is ill-equipped to handle.
This also introduces unnecessary (IMNSHO) aliasing in each client of
inodes and pages both.
I have a patch to fix NFS to cope with this by modifying the get_sb()
method to allow the filesystem to override the automatic selection of
super->s_root as the root dentry. However, Al Viro is leery of the patch
for some reason.
David
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Linux-cachefs mailing list
Linux-cachefs@redhat.com
http://www.redhat.com/mailman/listinfo/linux-cachefs
next prev parent reply other threads:[~2004-10-11 15:27 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-10-04 20:45 [PATCH] NFS using CacheFS Steve Dickson
2004-10-04 20:45 ` Steve Dickson
2004-10-04 21:53 ` Trond Myklebust
2004-10-04 21:53 ` Trond Myklebust
2004-10-05 10:01 ` David Howells
2004-10-05 10:01 ` David Howells
2004-10-08 4:36 ` Clemens Schwaighofer
2004-10-08 4:36 ` Clemens Schwaighofer
2004-10-08 11:22 ` Steve Dickson
2004-10-08 11:22 ` Steve Dickson
2004-10-08 15:39 ` Clemens Schwaighofer
2004-10-11 14:23 ` Martin Waitz
2004-10-11 14:23 ` Martin Waitz
2004-10-11 15:30 ` Trond Myklebust
2004-10-11 15:30 ` Trond Myklebust
2004-10-11 20:31 ` accessing/modifiying the nfs share files as different users bruce
2004-10-13 10:40 ` [Linux-cachefs] Re: [PATCH] NFS using CacheFS David Howells
2004-10-13 10:40 ` David Howells
2004-10-11 15:18 ` David Howells [this message]
2004-10-11 15:18 ` David Howells
2004-10-08 9:02 ` [Linux-cachefs] " David Howells
2004-10-08 9:02 ` David Howells
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