On Tue, 1 May 2007, Christoph Lameter wrote:
> On Tue, 1 May 2007, Hugh Dickins wrote:
>
> > Yes, to me it does. If it could be defaulted to on throughout the
> > -rcs, on every architecture, then I'd say that's "finishing work";
> > and we'd be safe knowing we could go back to slab in a hurry if
> > needed. But it hasn't reached that stage yet, I think.
>
> Why would we need to go back to SLAB if we have not switched to SLUB? SLUB
> is marked experimental and not the default.
I said above that I thought SLUB ought to be defaulted to on throughout
the -rcs: if we don't do that, we're not going to learn much from having
it in Linus' tree.
And perhaps that line which appends "PREEMPT " to an oops report ought
to append "SLUB " too, for so long as there's a choice.
> The only problems that I am aware of is(or was) the issue with arches
> modifying page struct fields of slab pages that SLUB needs for its own
> operations. And I thought it was all fixed since the powerpc guys were
> quiet and the patch was in for i386.
You're forgetting your unions in struct page: in the SPLIT_PTLOCK
case (NR_CPUS >= 4) the pagetable code is using spinlock_t ptl,
which overlays SLUB's first_page and slab pointers.
I just tried rebuilding powerpc with the SPLIT_PTLOCK cutover
edited to 8 cpus instead, and then no crash.
I presume the answer is just to extend your quicklist work to
powerpc's lowest level of pagetables. The only other architecture
which is using kmem_cache for them is arm26, which has
"#error SMP is not supported", so won't be giving this problem.
Hugh
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