Re: [PATCH 0/2] fix nfsd stable write implementation

[NeilBrown <neilb@suse.de>]

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On Fri, 26 Oct 2012 17:06:55 -0400 "J. Bruce Fields" <bfields@redhat.com>
wrote:

> From: "J. Bruce Fields" <bfields@redhat.com>
> 
> Peter pointed out to me that the nfs server is implementing stable
> writes by setting the O_SYNC flag.  I can't see why we couldn't write
> and then sync instead, but I don't know this stuff as well as I should;
> does the following look reasonable to people?

Bruce changed the code to implement stable writes by calling
vfs_fsync_range().  I can't see why we couldn't use O_SYNC instead.

It seems like you are making a change just for the sake of making a change.
Is there some reason that you think a separate 'sync' is more efficient than
using O_SYNC ?

As a general principle, I think it is best to give the file system as much
information as possible to that it can make whatever optimisation decisions
that it wants to.

Setting O_SYNC gives the filesystem more information than not, because it
allows it to change the behaviour of the 'write' request... though I don't
know if any filesystem actually uses the information.

Why the change?

NeilBrown

> 
> --b.
> 
> J. Bruce Fields (2):
>   nfsd: assume writeable exportabled filesystems have f_sync
>   nfsd: use vfs_fsync_range(), not O_SYNC, for stable writes
> 
>  fs/nfsd/vfs.c |   26 ++++++--------------------
>  1 file changed, 6 insertions(+), 20 deletions(-)
> 


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