Mount wsize and sync options

Mount wsize and sync options

[Amir Hermelin]

Hi,
I run an nfs server (RH9, kernel 2.4.20), and have experienced a =
behavior
with the wsize mount option that I have no explanation for. It appears =
that
when I use the sync option, the wsize is ignored (in default v3 UDP =
mount)
and is always 4k.

Maybe someone in the group can explain them to me or refer me to the =
'rules'
for using wsize and sync.

Thanks,
Amir.



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Re: Mount wsize and sync options

[Trond Myklebust]

P=E5 on , 19/05/2004 klokka 06:35, skreiv Amir Hermelin:
> Hi,
> I run an nfs server (RH9, kernel 2.4.20), and have experienced a behavior
> with the wsize mount option that I have no explanation for. It appears th=
at
> when I use the sync option, the wsize is ignored (in default v3 UDP mount=
)
> and is always 4k.

It is not ignored, it is just capped at PAGE_SIZE. 2k or 1k will
therefore work fine...

Cheers,
  Trond


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RE: Mount wsize and sync options

[Amir Hermelin]

Yes, It does accept 1 or 2k.  What's the reason for limiting synced =
writes
to page size?

-----Original Message-----
From: Trond Myklebust [mailto:trondmy@trondhjem.org] On Behalf Of Trond
Myklebust
Sent: Wednesday, May 19, 2004 6:11 PM
To: Amir Hermelin
Cc: nfs@lists.sourceforge.net
Subject: Re: [NFS] Mount wsize and sync options


P=E5 on , 19/05/2004 klokka 06:35, skreiv Amir Hermelin:
> Hi,
> I run an nfs server (RH9, kernel 2.4.20), and have experienced a=20
> behavior with the wsize mount option that I have no explanation for.=20
> It appears that when I use the sync option, the wsize is ignored (in=20
> default v3 UDP mount) and is always 4k.

It is not ignored, it is just capped at PAGE_SIZE. 2k or 1k will =
therefore
work fine...

Cheers,
  Trond



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RE: Mount wsize and sync options

[Trond Myklebust]

P=E5 on , 19/05/2004 klokka 16:20, skreiv Amir Hermelin:
> Yes, It does accept 1 or 2k.  What's the reason for limiting synced write=
s
> to page size?

It is because the VFS only writes one page at a time.

Now you could cluster those pages into one large RPC request (and this
is how O_SYNC normally works), but it turns out that some applications
do actually depend on the pages being synced to disk in the particular
order that they were written. The clustering technique unfortunately has
races that can ruin those ordering guarantees.

Cheers,
  Trond


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