Date: Wed, 28 Apr 2004 23:31:02 -0500 From: Alan Cox <alc@cs.rice.edu> To: Brian Fundakowski Feldman <green@FreeBSD.org> Cc: current@FreeBSD.org Subject: Re: VM wiring fixed Message-ID: <20040429043102.GN5199@cs.rice.edu> In-Reply-To: <200404290305.i3T35CW6001661@green.homeunix.org> References: <20040429022401.GJ5199@cs.rice.edu> <200404290305.i3T35CW6001661@green.homeunix.org>
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On Wed, Apr 28, 2004 at 11:05:12PM -0400, Brian Fundakowski Feldman wrote:
> Alan Cox <alc@cs.rice.edu> wrote:
> > On Wed, Apr 28, 2004 at 08:08:17PM -0400, Brian Fundakowski Feldman wrote:
> > > There are several severe wiring bugs in -CURRENT that I believe I have fixed.
> > > Please test/review as appropriate if you're affected by any of them. This
> > > is a superset of the previous patch which just mostly-fixed mlockall(2).
> > >
> > > * MAP_FUTUREWIRE was not unset in vmspace_dofree(), causing the next process
> > > to use that vmspace to wire all of its memory.
> >
> > Would setting flags to 0 in vmspace_alloc() accomplish the same?
>
> Yeah, same deal, except since we're optimizing by only clearing/
> reinitializing some fields for the vmspace-zone objects, it makes a little
> more sense IMO to have it in the vmspace_dofree().
>
To be honest, I would prefer to see this done by initializing flags to
zero in vmspace_alloc(). I don't see how setting a field to zero at
allocation time is less efficient than calling
static __inline void
vm_map_modflags(vm_map_t map, vm_flags_t set, vm_flags_t clear)
{
map->flags = (map->flags | set) & ~clear;
}
at deallocation time. In fact, I would expect initializing the field
to zero at initialization time to be faster. It is also the more
conventional and conservative approach. (For example, it would
protect us from a future change to UMA such that the pages used to
fill a zone are no longer prezeroed.)
I'll follow up on the other questions later. I would encourage you to
go ahead and commit the fix to flags.
Regards,
Alan
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