On Wed, 2 May 2007, Hugh Dickins wrote:
> > 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.
I'd rather be careful with that..... mm is enough for now. Why go to the
extremes immediately. If it is an option then people can gradually start
testing with it.
> > 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.
Uhhh.... Right. So SLUB wont work if the lowest page table block is
managed via slabs.
> 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
I am not sure how PowerPCs lower pagetable pages work. If they are of
PAGE_SIZE then this is no problem.
> which is using kmem_cache for them is arm26, which has
> "#error SMP is not supported", so won't be giving this problem.
Ahh. Good.
But these are arch specific problems. We could use
ARCH_USES_SLAB_PAGE_STRUCT to disable SLUB on these platforms.
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