On Wed, 2 May 2007, Hugh Dickins wrote:

quoted

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.
 

quoted

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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