Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933592AbcJZTWX (ORCPT ); Wed, 26 Oct 2016 15:22:23 -0400 Received: from mail-yb0-f175.google.com ([209.85.213.175]:35435 "EHLO mail-yb0-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932519AbcJZTWO (ORCPT ); Wed, 26 Oct 2016 15:22:14 -0400 MIME-Version: 1.0 In-Reply-To: References: <1477503688-69191-1-git-send-email-thgarnie@google.com> From: Thomas Garnier Date: Wed, 26 Oct 2016 12:22:12 -0700 Message-ID: Subject: Re: [PATCH v1] memcg: Prevent caches to be both OFF_SLAB & OBJFREELIST_SLAB To: Christoph Lameter Cc: Pekka Enberg , David Rientjes , Joonsoo Kim , Andrew Morton , Linux-MM , LKML , Greg Thelen Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2986 Lines: 82 On Wed, Oct 26, 2016 at 12:08 PM, Christoph Lameter wrote: > Hmmm...Doesnt this belong into memcg_create_kmem_cache() or into > kmem_cache_create() in mm/slab_common.h? Definitely not in an allocator > specific function since this is an issue for all allocators. > > memcg_create_kmem_cache() simply assumes that it can pass flags from the > kmem_cache structure to kmem_cache_create(). However, those flags may > contain slab specific options. > > kmem_cache_create() could filter out flags that cannot be specified. That make sense. > > Maybe create SLAB_FLAGS_PERMITTED in linux/mm/slab.h and mask other bits > out in kmem_cache_create()? > > Slub also has internal flags and those also should not be passed to > kmem_cache_create(). If we define the valid ones we can mask them out. > > The cleanest approach would be if kmem_cache_create() would reject invalid > flags and fail and if memcg_create_kmem_cache() would mask out the invalid > flags using SLAB_FLAGS_PERMITTED or so. Okay, I think for SLAB we can allow everything except the two flags mentioned here. Should I deny certain flags for SLUB? I can allow everything for now. > > > > On Wed, 26 Oct 2016, Thomas Garnier wrote: > >> While testing OBJFREELIST_SLAB integration with pagealloc, we found a >> bug where kmem_cache(sys) would be created with both CFLGS_OFF_SLAB & >> CFLGS_OBJFREELIST_SLAB. >> >> The original kmem_cache is created early making OFF_SLAB not possible. >> When kmem_cache(sys) is created, OFF_SLAB is possible and if pagealloc >> is enabled it will try to enable it first under certain conditions. >> Given kmem_cache(sys) reuses the original flag, you can have both flags >> at the same time resulting in allocation failures and odd behaviors. >> >> The proposed fix removes these flags by default at the entrance of >> __kmem_cache_create. This way the function will define which way the >> freelist should be handled at this stage for the new cache. >> >> Fixes: b03a017bebc4 ("mm/slab: introduce new slab management type, OBJFREELIST_SLAB") >> Signed-off-by: Thomas Garnier >> Signed-off-by: Greg Thelen >> --- >> Based on next-20161025 >> --- >> mm/slab.c | 8 ++++++++ >> 1 file changed, 8 insertions(+) >> >> diff --git a/mm/slab.c b/mm/slab.c >> index 3c83c29..efe280a 100644 >> --- a/mm/slab.c >> +++ b/mm/slab.c >> @@ -2027,6 +2027,14 @@ __kmem_cache_create (struct kmem_cache *cachep, unsigned long flags) >> int err; >> size_t size = cachep->size; >> >> + /* >> + * memcg re-creates caches with the flags of the originals. Remove >> + * the freelist related flags to ensure they are re-defined at this >> + * stage. Prevent having both flags on edge cases like with pagealloc >> + * if the original cache was created too early to be OFF_SLAB. >> + */ >> + flags &= ~(CFLGS_OBJFREELIST_SLAB|CFLGS_OFF_SLAB); >> + >> #if DEBUG >> #if FORCED_DEBUG >> /* >> -- Thomas