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Date: Wed, 27 Nov 2013 19:21:24 -0500 (EST)
From: Rick Macklem <rmacklem@uoguelph.ca>
To: Kirk McKusick <mckusick@mckusick.com>
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Subject: Re: RFC: NFS client patch to reduce sychronous writes
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Oops, I did my usual and forgot to attach the test program.
Here it is, rick

----- Original Message -----
> > Date: Wed, 27 Nov 2013 17:50:48 -0500 (EST)
> > From: Rick Macklem <rmacklem@uoguelph.ca>
> > To: Konstantin Belousov <kostikbel@gmail.com>
> > Subject: Re: RFC: NFS client patch to reduce sychronous writes
> > 
> > Kostik wrote:
> >> Sorry, I do not understand the question. mmap(2) itself does not
> >> change
> >> file size.  But if mmaped area includes the last page, I still
> >> think
> >> that the situation I described before is possible.
> > 
> > Yes, I'll need to look at this. If it is a problem, all I can think
> > of
> > is bzeroing all new pages when they're allocated to the buffer
> > cache.
> > 
> > Thanks for looking at it, rick
> > ps: Btw, jhb@'s patch didn't have the bzeroing in it.
> 
> The ``fix'' of bzero'ing every buffer cache page was made to UFS/FFS
> for this problem and it killed write performance of the filesystem
> by nearly half. We corrected this by only doing the bzero when the
> file is mmap'ed which helped things considerably (since most files
> being written are not also bmap'ed).
> 
> 	Kirk
>