Re: [PATCH] SLOB allocator imcompatible SLAB

[Nick Piggin]

Matt Mackall wrote:
> On Tue, Jun 26, 2007 at 02:06:15PM +1000, Nick Piggin wrote:
>
> > Yoshinori Sato wrote:
> >
> > > At Fri, 22 Jun 2007 09:56:35 -0500,
> > > Matt Mackall wrote:
> > >
> > >
> > > > On Fri, Jun 22, 2007 at 05:08:07PM +0900, Yoshinori Sato wrote:
> > > >
> > > >
> > > > > Because the page which SLOB allocator got does not have PG_slab,
> > > >
> > > > This is for a NOMMU system?
> > >
> > >
> > > Yes.
> > >
> > >
> > >
> > > > You're using an old kernel with an old version of SLOB. SLOB in newer
> > > > kernels actually sets per-page flags. Nick, can you see any reason not
> > > > to s/PG_active/PG_slab/ in the current code?
> >
> > The problem with this is that PG_private is used only for the SLOB
> > part of the allocator and not the bigblock part.
>
>
> That's fine, at least for the purposes of kobjsize. We only mark
> actual SLOB-managed pages, kobjsize assumes the rest are alloc_pages
> and that's indeed what they are.

OK, but that only makes it work in this case. I think we should
either call PG_slab part of the kmem/kmalloc API and implement
that, or say it isn't and make nommu do something else?


> > We _could_ just bite the bullet and have SLOB set PG_slab, however
> > that would encouarage more users of this flag which we should hope
> > to get rid of one day.
> >
> > The real problem is that nommu wants to get the size of either
> > kmalloc or alloc_pages objects and it needs to differentiate
> > between them. So I would rather nommu to take its own page flag
> > (could overload PG_swapcache, perhaps?), and set that flag on
> > pages it allocates directly, then uses that to determine whether
> > to call ksize or not.
>
>
> I think we already established on the last go-round that the kobjsize
> scheme was rather hopelessly broken anyway. 

I can't remember, but that would be another good reason to confine
it to nommu.c wouldn't it?

--
SUSE Labs, Novell Inc.
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