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Subject: Re: a little improvement  for vmalloc
From: Anton Altaparmakov <aia21@cam.ac.uk>
To: Andrew Morton <akpm@osdl.org>
Cc: Zhonglin Zhang <zhonglinzh@mobilesoft.com.cn>,
       lkml <linux-kernel@vger.kernel.org>
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References: <1104981532.628.10.camel@milo>
	 <20050105193827.12d83341.akpm@osdl.org>
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Organization: University of Cambridge Computing Service, UK
Date: Thu, 06 Jan 2005 09:26:41 +0000
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On Wed, 2005-01-05 at 19:38 -0800, Andrew Morton wrote:
> Zhonglin Zhang <zhonglinzh@mobilesoft.com.cn> wrote:
> >
> > In FUNCTION __vmalloc ,
> > 
> >  There is a statement;
> > 
> >  if (!size || (size >> PAGE_SHIFT) > num_physpages)
> >          return NULL;
> 
> Probably the second part of the test should be removed.  If the requested
> area size is
> 
> a) less than the size of the vmalloc arena and
> 
> b) more than the number of allocatable pages
> 
> then yes, the machine will have a ton of trouble allocating the memory and
> will actually lock up.
> 
> But the only way that will happen is if some code is made to do a large
> number of smaller vmallocs.  Nobody does a huge single vmalloc like that.

I thought that second test was to avoid stupid bugs that may exist in
some random (perhaps ex-tree) modules that would otherwise cause the
machine to lockup...

Best regards,

        Anton
-- 
Anton Altaparmakov <aia21 at cam.ac.uk> (replace at with @)
Unix Support, Computing Service, University of Cambridge, CB2 3QH, UK
Linux NTFS maintainer / IRC: #ntfs on irc.freenode.net
WWW: http://linux-ntfs.sf.net/ & http://www-stu.christs.cam.ac.uk/~aia21/

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