From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751009AbcFNIJd (ORCPT ); Tue, 14 Jun 2016 04:09:33 -0400 Received: from LGEAMRELO11.lge.com ([156.147.23.51]:53579 "EHLO lgeamrelo11.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750805AbcFNIJ3 (ORCPT ); Tue, 14 Jun 2016 04:09:29 -0400 X-Original-SENDERIP: 156.147.1.126 X-Original-MAILFROM: iamjoonsoo.kim@lge.com X-Original-SENDERIP: 10.177.222.138 X-Original-MAILFROM: iamjoonsoo.kim@lge.com Date: Tue, 14 Jun 2016 17:11:25 +0900 From: Joonsoo Kim To: Geert Uytterhoeven Cc: Andrew Morton , Christoph Lameter , Pekka Enberg , David Rientjes , Jesper Dangaard Brouer , Linux MM , "linux-kernel@vger.kernel.org" , linux-renesas-soc@vger.kernel.org, "linux-arm-kernel@lists.infradead.org" Subject: Re: Boot failure on emev2/kzm9d (was: Re: [PATCH v2 11/11] mm/slab: lockless decision to grow cache) Message-ID: <20160614081125.GA17700@js1304-P5Q-DELUXE> References: <20160614062456.GB13753@js1304-P5Q-DELUXE> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jun 14, 2016 at 09:31:23AM +0200, Geert Uytterhoeven wrote: > Hi Joonsoo, > > On Tue, Jun 14, 2016 at 8:24 AM, Joonsoo Kim wrote: > > On Mon, Jun 13, 2016 at 09:43:13PM +0200, Geert Uytterhoeven wrote: > >> On Tue, Apr 12, 2016 at 6:51 AM, wrote: > >> > From: Joonsoo Kim > >> > To check whther free objects exist or not precisely, we need to grab a > >> > lock. But, accuracy isn't that important because race window would be > >> > even small and if there is too much free object, cache reaper would reap > >> > it. So, this patch makes the check for free object exisistence not to > >> > hold a lock. This will reduce lock contention in heavily allocation case. > >> > > >> > Note that until now, n->shared can be freed during the processing by > >> > writing slabinfo, but, with some trick in this patch, we can access it > >> > freely within interrupt disabled period. > >> > > >> > Below is the result of concurrent allocation/free in slab allocation > >> > benchmark made by Christoph a long time ago. I make the output simpler. > >> > The number shows cycle count during alloc/free respectively so less is > >> > better. > >> > > >> > * Before > >> > Kmalloc N*alloc N*free(32): Average=248/966 > >> > Kmalloc N*alloc N*free(64): Average=261/949 > >> > Kmalloc N*alloc N*free(128): Average=314/1016 > >> > Kmalloc N*alloc N*free(256): Average=741/1061 > >> > Kmalloc N*alloc N*free(512): Average=1246/1152 > >> > Kmalloc N*alloc N*free(1024): Average=2437/1259 > >> > Kmalloc N*alloc N*free(2048): Average=4980/1800 > >> > Kmalloc N*alloc N*free(4096): Average=9000/2078 > >> > > >> > * After > >> > Kmalloc N*alloc N*free(32): Average=344/792 > >> > Kmalloc N*alloc N*free(64): Average=347/882 > >> > Kmalloc N*alloc N*free(128): Average=390/959 > >> > Kmalloc N*alloc N*free(256): Average=393/1067 > >> > Kmalloc N*alloc N*free(512): Average=683/1229 > >> > Kmalloc N*alloc N*free(1024): Average=1295/1325 > >> > Kmalloc N*alloc N*free(2048): Average=2513/1664 > >> > Kmalloc N*alloc N*free(4096): Average=4742/2172 > >> > > >> > It shows that allocation performance decreases for the object size up to > >> > 128 and it may be due to extra checks in cache_alloc_refill(). But, with > >> > considering improvement of free performance, net result looks the same. > >> > Result for other size class looks very promising, roughly, 50% performance > >> > improvement. > >> > > >> > v2: replace kick_all_cpus_sync() with synchronize_sched(). > >> > > >> > Signed-off-by: Joonsoo Kim > >> > >> I've bisected a boot failure (no output at all) in v4.7-rc2 on emev2/kzm9d > >> (Renesas dual Cortex A9) to this patch, which is upstream commit > >> 801faf0db8947e01877920e848a4d338dd7a99e7. > >> > >> I've attached my .config. I don't know if it also happens with > >> shmobile_defconfig, as something went wrong with my remote access to the board, > >> preventing further testing. I also couldn't verify if the issue persists in > >> v4.7-rc3. > > In the mean time, I've verified it also happens with shmobile_defconfig. > > >> > >> Do you have a clue? > > > > I don't have yet. Could you help me to narrow down the problem? > > Following diff is half-revert change to check that synchronize_sched() > > has no problem. > > Thanks! > > Unfortunately the half revert is not sufficient. The full revert is. Thanks for quick testing! Could I ask one more time to check that synchronize_sched() is root cause of the problem? Testing following two diffs will be helpful to me. Thanks. ------->8-------- diff --git a/mm/slab.c b/mm/slab.c index 763096a..d892364 100644 --- a/mm/slab.c +++ b/mm/slab.c @@ -965,7 +965,7 @@ static int setup_kmem_cache_node(struct kmem_cache *cachep, * freed after synchronize_sched(). */ if (force_change) - synchronize_sched(); + kick_all_cpus_sync(); fail: kfree(old_shared); ------->8------ diff --git a/mm/slab.c b/mm/slab.c index 763096a..38d99c2 100644 --- a/mm/slab.c +++ b/mm/slab.c @@ -964,8 +964,6 @@ static int setup_kmem_cache_node(struct kmem_cache *cachep, * guaranteed to be valid until irq is re-enabled, because it will be * freed after synchronize_sched(). */ - if (force_change) - synchronize_sched(); fail: kfree(old_shared);