Message-Id: <200603090033.k290XBg13472@unix-os.sc.intel.com>
From: "Chen, Kenneth W" <kenneth.w.chen@intel.com>
To: "'David Gibson'" <david@gibson.dropbear.id.au>
Cc: "'Zhang, Yanmin'" <yanmin_zhang@linux.intel.com>,
       <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH] ftruncate on huge page couldn't extend hugetlb file
Date: Wed, 8 Mar 2006 16:33:10 -0800
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David Gibson wrote on Wednesday, March 08, 2006 4:23 PM
> > But you already make reservation at mmap time.  If you reserve it again
> > when extending the file, won't you double count?
> 
> Well, I'd generally expect extending truncate() to come before mmap(),
> but in any case hugetlb_extend_reservation() is safe against double
> counting (it's idempotent if called twice with the same number of
> pages).  The semantics are "ensure the this many pages total are
> guaranteed available, that is, either reserved or already
> instantiated".

It's kind of peculiar that kernel reserve hugetlb page at the time of
extending truncate.  Maybe there is a close correlation between mmap
size to the file size.  But these two aren't the same and and shouldn't
be mixed.

- Ken

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