Date: Wed, 27 Nov 2013 19:21:24 -0500 (EST) From: Rick Macklem <rmacklem@uoguelph.ca> To: Kirk McKusick <mckusick@mckusick.com> Cc: FreeBSD FS <freebsd-fs@freebsd.org> Subject: Re: RFC: NFS client patch to reduce sychronous writes Message-ID: <66384815.22292870.1385598084659.JavaMail.root@uoguelph.ca> In-Reply-To: <201311272320.rARNKEKQ045789@chez.mckusick.com>
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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 >
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