From patchwork Tue Jun 14 06:24:57 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Joonsoo Kim X-Patchwork-Id: 9175047 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id 2DE246075D for ; Tue, 14 Jun 2016 06:24:41 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 1EF3028179 for ; Tue, 14 Jun 2016 06:24:41 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 13C692821D; Tue, 14 Jun 2016 06:24:41 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-4.2 required=2.0 tests=BAYES_00, RCVD_IN_DNSWL_MED autolearn=unavailable version=3.3.1 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.9]) (using TLSv1.2 with cipher AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.wl.linuxfoundation.org (Postfix) with ESMTPS id 82DD428179 for ; Tue, 14 Jun 2016 06:24:40 +0000 (UTC) Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.80.1 #2 (Red Hat Linux)) id 1bChks-0002oL-LA; Tue, 14 Jun 2016 06:23:18 +0000 Received: from lgeamrelo13.lge.com ([156.147.23.53]) by bombadil.infradead.org with esmtp (Exim 4.80.1 #2 (Red Hat Linux)) id 1bChkp-0002kI-LN for linux-arm-kernel@lists.infradead.org; Tue, 14 Jun 2016 06:23:17 +0000 Received: from unknown (HELO lgeamrelo02.lge.com) (156.147.1.126) by 156.147.23.53 with ESMTP; 14 Jun 2016 15:22:51 +0900 X-Original-SENDERIP: 156.147.1.126 X-Original-MAILFROM: iamjoonsoo.kim@lge.com Received: from unknown (HELO localhost) (10.177.222.138) by 156.147.1.126 with ESMTP; 14 Jun 2016 15:22:51 +0900 X-Original-SENDERIP: 10.177.222.138 X-Original-MAILFROM: iamjoonsoo.kim@lge.com Date: Tue, 14 Jun 2016 15:24:57 +0900 From: Joonsoo Kim To: Geert Uytterhoeven Subject: Re: Boot failure on emev2/kzm9d (was: Re: [PATCH v2 11/11] mm/slab: lockless decision to grow cache) Message-ID: <20160614062456.GB13753@js1304-P5Q-DELUXE> References: MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20160613_232316_043001_80EEA07F X-CRM114-Status: GOOD ( 23.77 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.20 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-renesas-soc@vger.kernel.org, David Rientjes , "linux-kernel@vger.kernel.org" , Pekka Enberg , Linux MM , Jesper Dangaard Brouer , Andrew Morton , Christoph Lameter , "linux-arm-kernel@lists.infradead.org" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+patchwork-linux-arm=patchwork.kernel.org@lists.infradead.org X-Virus-Scanned: ClamAV using ClamSMTP On Mon, Jun 13, 2016 at 09:43:13PM +0200, Geert Uytterhoeven wrote: > Hi Joonsoo, Hello, > > 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. > > 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. ----->8----- diff --git a/mm/slab.c b/mm/slab.c index 763096a..257a0eb 100644 --- a/mm/slab.c +++ b/mm/slab.c @@ -3016,9 +3016,6 @@ static void *cache_alloc_refill(struct kmem_cache *cachep, gfp_t flags) n = get_node(cachep, node); BUG_ON(ac->avail > 0 || !n); - shared = READ_ONCE(n->shared); - if (!n->free_objects && (!shared || !shared->avail)) - goto direct_grow; spin_lock(&n->list_lock); shared = READ_ONCE(n->shared); @@ -3047,7 +3044,6 @@ alloc_done: spin_unlock(&n->list_lock); fixup_objfreelist_debug(cachep, &list); -direct_grow: if (unlikely(!ac->avail)) { /* Check if we can use obj in pfmemalloc slab */ if (sk_memalloc_socks()) {