From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Wed, 2 May 2007 10:01:41 -0700 (PDT) From: Christoph Lameter Subject: Re: 2.6.22 -mm merge plans: slub In-Reply-To: Message-ID: References: <20070430162007.ad46e153.akpm@linux-foundation.org> <20070501125559.9ab42896.akpm@linux-foundation.org> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org Return-Path: To: Hugh Dickins Cc: Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org List-ID: 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. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org