From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Mon, 20 Nov 2006 22:59:15 -0800 From: Randy Dunlap Subject: Re: build error: sparsemem + SLOB Message-Id: <20061120225915.0d9777d6.randy.dunlap@oracle.com> In-Reply-To: <20061121143253.51B5.Y-GOTO@jp.fujitsu.com> References: <20061120183632.GD4797@waste.org> <20061121143253.51B5.Y-GOTO@jp.fujitsu.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Yasunori Goto Cc: Matt Mackall , Hugh Dickins , Christoph Lameter , linux-mm@kvack.org, Pekka Enberg List-ID: On Tue, 21 Nov 2006 14:57:23 +0900 Yasunori Goto wrote: > > On Mon, Nov 20, 2006 at 05:28:24PM +0000, Hugh Dickins wrote: > > > On Mon, 20 Nov 2006, Christoph Lameter wrote: > > > > > > > > As far as I can tell SLOB is fundamentally racy since it does not support > > > > SLAB_DESTROY_BY_RCU correctly. F.e. The constructor for the anon_vma will > > > > be called on alloc without regard for RCU, we free an item and reuse it > > > > without regard to RCU. This can potentially mess up the anon_vma locking > > > > state while we access it. > > > > > > Good find! > > > > > > > Is SLOB used at all or have we been lucky so far? > > > > > > Lucky so far. Well, we'd actually have to be quite unlucky to ever > > > see what page_lock_anon_vma/SLAB_DESTROY_BY_RCU are guarding against. > > > > > > But you're absolutely right that users should not be exposed to such > > > unsafety. I'd say SLOB should be disallowed if SMP. > > > > SLOB is an O(N) allocator and is pretty poorly suited to running on > > anything like a modern desktop. Disallowing if SMP is probably > > reasonable, as even machines with multicore ARM or MIPS will probably > > have enough memory to make SLOB a bit painful. > > Ok. It's simple. This is fix. > > ---- > > This is to disallow to make SLOB with SMP or SPARSEMEM. > This avoids latent troubles of SLOB with SLAB_DESTROY_BY_RCU. > And fix compile error. > > This patch is for 2.6.19-rc5-mm2. > > > Signed-off-by: Yasunori Goto Acked-by: Randy Dunlap Thanks. > ---- > init/Kconfig | 2 +- > 1 files changed, 1 insertion(+), 1 deletion(-) > > Index: 19-rc5-mm2/init/Kconfig > =================================================================== > --- 19-rc5-mm2.orig/init/Kconfig 2006-11-21 13:41:31.000000000 +0900 > +++ 19-rc5-mm2/init/Kconfig 2006-11-21 14:21:31.000000000 +0900 > @@ -465,7 +465,7 @@ config SHMEM > > config SLAB > default y > - bool "Use full SLAB allocator" if EMBEDDED > + bool "Use full SLAB allocator" if (EMBEDDED && !SMP && !SPARSEMEM) > help > Disabling this replaces the advanced SLAB allocator and > kmalloc support with the drastically simpler SLOB allocator. > > > -- --- ~Randy -- 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