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Re: Severe problem with formatted write
- From: Steve Kargl <sgk at troutmask dot apl dot washington dot edu>
- To: Paul Thomas <paulthomas2 at wanadoo dot fr>, Fran?ois-Xavier Coudert <fxcoudert at gmail dot com>, Steven Bosscher <stevenb at suse dot de>, "fortran at gcc dot gnu dot org" <fortran at gcc dot gnu dot org>
- Date: Mon, 1 Aug 2005 14:47:15 -0700
- Subject: Re: Severe problem with formatted write
- References: <756DFD3DE8F1D411A59A00306E06E84702C427A5@drfccad.cad.cea.fr> <200507211211.32349.stevenb@suse.de> <200507211253.25515.stevenb@suse.de> <42E24ECA.6000307@wanadoo.fr> <19c433eb050725063511f403be@mail.gmail.com> <42E51A48.1070700@wanadoo.fr> <42EE7747.4040407@wanadoo.fr> <20050801194507.GA12933@troutmask.apl.washington.edu> <20050801211422.GA5964@vipunen.hut.fi>
On Tue, Aug 02, 2005 at 12:14:23AM +0300, Janne Blomqvist wrote:
> On Mon, Aug 01, 2005 at 12:45:07PM -0700, Steve Kargl wrote:
> > Is RH9 using a mmap file? This could be strange interaction
> > between mmap and truncating a file. The FreeBSD manual page
> > has the following:
> >
> > WARNING! Extending a file with ftruncate(2), thus creating a big hole,
> > and then filling the hole by modifying a shared mmap() can lead to severe
> > file fragmentation. In order to avoid such fragmentation you should
> > always pre-allocate the file's backing store by write()ing zero's into
> > the newly extended area prior to modifying the area via your mmap().
> > The fragmentation problem is especially sensitive to MAP_NOSYNC pages,
> > because pages may be flushed to disk in a totally random order.
>
> Sorry if I sound rude, but uh, why again are we bothering with mmap?
You're not being rude. FWIW, I agree with your assessment, and
I think we should disable the use of mmap at the moment.
(Janne's mmap points deleted.)
> PS: Thanks Steve for reviewing my FLUSH patch, and sorry for
> forgetting to mention the IOMSG issue.
Don't get discouraged. I'm still working on/with the
patch. Time is very limited at the moment. The only
problems I've seen so far are formatting issues, which
I can easily fix.
--
Steve