Re: [PATCH v2 1/5] fat: allocate persistent inode numbers

From: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
To: Namjae Jeon <linkinjeon@gmail.com>
Cc: "Steven J. Magnani" <steve@digidescorp.com>,
	Al Viro <viro@zeniv.linux.org.uk>,
	akpm@linux-foundation.org, bfields@fieldses.org,
	linux-kernel@vger.kernel.org,
	Namjae Jeon <namjae.jeon@samsung.com>,
	Ravishankar N <ravi.n1@samsung.com>,
	Amit Sahrawat <a.sahrawat@samsung.com>
Subject: Re: [PATCH v2 1/5] fat: allocate persistent inode numbers
Date: Mon, 10 Sep 2012 23:00:02 +0900	[thread overview]
Message-ID: <87har6kmfx.fsf@devron.myhome.or.jp> (raw)
In-Reply-To: <CAKYAXd-k4yVV3h8k0kcFMsyGnOVckYRjXi8fkZrLtjuWVi7Eqw@mail.gmail.com> (Namjae Jeon's message of "Mon, 10 Sep 2012 21:03:46 +0900")

Namjae Jeon <linkinjeon@gmail.com> writes:

> Yes, It is  true(current VFAT of -mm tree is not stable). Although we
> set lookupcache=none while mounting, ESTALE error can still occur in
> rename case.
> So there still remain ESTALE error issue from rename case on current -mm tree.
> plz See the step as the following
> 1. on client write to file.
> 2. on client, move/rename file.
> 3. on server, do drop_caches. etc to somehow evict indoe number so
> that it gets new inode number
> 4. on client, resume the program to write to file. write will fail
> (write: Stale NFS file handle)

Since rename() will be disabled on stable ino patches, this will be
unfixable, so rather maybe it is worse.

Did you checked why it returns -ESTALE?  Or rename() issue also is
unfixable on -mm?

> And ......
> If we mount NFS with lookupcache=none, FAT file lookup performance is
> severely dropped.
> LOOKUP performance is very poor on slow network and slow device. I do
> not recommend to disable lookup cache on NFS.
> And that is why reconstructing inode is already implemented in other
> filesystem (e.g. EXT4, XFS etc..)
> Currently lookupcache is enabled by default in NFS, it means users
> already have disclosed and experienced ESTALE issues on NFS over VFAT.
>
> I agree wth you to make NFS over VFAT read-only filesystem to avoid all issues.
> Eventually we can make it writable with rename limitation when we
> decide that it is pretty stable in mainline.
> So, I suggest to add 'nfs_ro' mount option instead of 'nfs' option.

-mm seems to be more stable than I thought. As he said, sounds like
rename() is an only known issue on -mm, true?

And are you tried https://lkml.org/lkml/2012/6/29/381 patches? It sounds
like to improve performance by enabling lookupcache. I'd like to be
knowing the critical reason we have to replace it.

Thanks.
-- 
OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>