Re: [PATCH]

[Daniel Phillips <phillips@bonn-fries.net>]

On August 15, 2001 07:40 pm, Linus Torvalds wrote:
> On Wed, 15 Aug 2001, Ben LaHaise wrote:
> >
> > The patch below enables vma merging for a couple of additional cases with
> > anon mmaps as glibc has a habit of passing in differing flags for some
> > cases (ie memory remapping, extending specific malloc blocks, etc).  This
> > is to help Mozilla which ends up with thousands of vma's that are
> > sequential and anonymous, but unmerged.  There may still be issues with
> > mremap, but I think this is a step in the right direction.
> 
> Good catch.
> 
> However, I really think we should just mask those bits out in general:
> we've already used them up by this time, and they make no sense at all to
> maintain in the VMA either, so it looks like it would be a cleaner (and
> shorter) patch to just do
> 
> 	/* get rid of mmap-time-only flags */
> 	vm_flags &= ~(MAP_NORESERVE | MAP_FIXED);
> 
> just after we've checked the MAP_NORESERVE bit, and just before we check
> whether we can expand an old mapping. That way the (now meaningless) bits
> don't end up as noise in the vma->vm_flags, AND we guarantee that merging
> doesn't merge two fields that have different "noise" in their vm_flags.

Another one in that category is BH_New which we use only immediately after
*_get_block, afterwards it dangles meaninglessly.  Not a bug, but
misleading.

--
Daniel
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