From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f199.google.com (mail-pf0-f199.google.com [209.85.192.199]) by kanga.kvack.org (Postfix) with ESMTP id 97406828FF for ; Tue, 14 Jun 2016 02:22:53 -0400 (EDT) Received: by mail-pf0-f199.google.com with SMTP id g62so230088577pfb.3 for ; Mon, 13 Jun 2016 23:22:53 -0700 (PDT) Received: from lgeamrelo13.lge.com (LGEAMRELO13.lge.com. [156.147.23.53]) by mx.google.com with ESMTP id ok15si12761128pab.146.2016.06.13.23.22.51 for ; Mon, 13 Jun 2016 23:22:52 -0700 (PDT) Date: Tue, 14 Jun 2016 15:24:57 +0900 From: Joonsoo Kim 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-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: 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" 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()) { -- 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