Re: Read/Write NFS I/O performance degraded by FLUSH_STABLE page flushing

Chuck Lever
2009-06-02T15:00:50Z

On May 30, 2009, at 9:02 AM, Greg Banks wrote:
> On Sat, May 30, 2009 at 10:26 PM, Trond Myklebust
> <trond.myklebust@fys.uio.no> wrote:
>> On Sat, 2009-05-30 at 10:22 +1000, Greg Banks wrote:
>>> On Sat, May 30, 2009 at 3:35 AM, Trond Myklebust
>>> <trond.myklebust@fys.uio.no> wrote:
>>>> On Fri, 2009-05-29 at 13:25 -0400, Brian R Cowan wrote:
>>>>>
>>>
>>
>> Firstly, the server only uses O_SYNC if you turn off write gathering
>> (a.k.a. the 'wdelay' option). The default behaviour for the Linux nfs
>> server is to always try write gathering and hence no O_SYNC.
>
> Well, write gathering is a total crock that AFAICS only helps
> single-file writes on NFSv2. For today's workloads all it does is
> provide a hotspot on the two global variables that track writes in an
> attempt to gather them. Back when I worked on a server product,
> no_wdelay was one of the standard options for new exports.

Really? Even for NFSv3/4 FILE_SYNC? I can understand that it
wouldn't have any real effect on UNSTABLE.

--
Chuck Lever
chuck[dot]lever[at]oracle[dot]com