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

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Date:	Mon, 10 Sep 2012 23:00:02 +0900
From:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
To:	Namjae Jeon <linkinjeon@...il.com>
Cc:	"Steven J. Magnani" <steve@...idescorp.com>,
	Al Viro <viro@...iv.linux.org.uk>, akpm@...ux-foundation.org,
	bfields@...ldses.org, linux-kernel@...r.kernel.org,
	Namjae Jeon <namjae.jeon@...sung.com>,
	Ravishankar N <ravi.n1@...sung.com>,
	Amit Sahrawat <a.sahrawat@...sung.com>
Subject: Re: [PATCH v2 1/5] fat: allocate persistent inode numbers

Namjae Jeon <linkinjeon@...il.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@...l.parknet.co.jp>
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