From: Joonsoo Kim <iamjoonsoo.kim@lge.com>
To: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Christoph Lameter <cl@linux.com>,
Pekka Enberg <penberg@kernel.org>,
David Rientjes <rientjes@google.com>,
Jesper Dangaard Brouer <brouer@redhat.com>,
Linux MM <linux-mm@kvack.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
linux-renesas-soc@vger.kernel.org,
"linux-arm-kernel@lists.infradead.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)
Date: Tue, 14 Jun 2016 15:24:57 +0900 [thread overview]
Message-ID: <20160614062456.GB13753@js1304-P5Q-DELUXE> (raw)
In-Reply-To: <CAMuHMdXC=zEjbZADE5wELjOq_kBiFNewpdUrMCe8d3Utu98h8A@mail.gmail.com>
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, <js1304@gmail.com> wrote:
> > From: Joonsoo Kim <iamjoonsoo.kim@lge.com>
> >
> > 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 <iamjoonsoo.kim@lge.com>
>
> 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()) {
next prev parent reply other threads:[~2016-06-14 6:22 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-13 19:43 Boot failure on emev2/kzm9d (was: Re: [PATCH v2 11/11] mm/slab: lockless decision to grow cache) Geert Uytterhoeven
2016-06-14 6:24 ` Joonsoo Kim [this message]
2016-06-14 7:31 ` Geert Uytterhoeven
2016-06-14 8:11 ` Joonsoo Kim
2016-06-14 10:45 ` Geert Uytterhoeven
2016-06-15 2:23 ` Joonsoo Kim
2016-06-15 8:39 ` Geert Uytterhoeven
2016-06-20 6:39 ` Joonsoo Kim
2016-06-20 13:12 ` Paul E. McKenney
2016-06-21 6:43 ` Joonsoo Kim
2016-06-21 12:54 ` Paul E. McKenney
2016-06-22 0:52 ` Joonsoo Kim
2016-06-22 3:15 ` Paul E. McKenney
2016-06-22 15:01 ` Geert Uytterhoeven
2016-06-22 19:08 ` Paul E. McKenney
2016-06-23 0:49 ` Paul E. McKenney
2016-06-23 2:37 ` Joonsoo Kim
2016-06-23 2:47 ` Paul E. McKenney
2016-06-23 2:53 ` Paul E. McKenney
2016-06-28 0:12 ` Paul E. McKenney
2016-06-28 8:33 ` Joonsoo Kim
2016-06-29 14:54 ` Geert Uytterhoeven
2016-06-29 16:44 ` Paul E. McKenney
2016-06-29 17:52 ` Geert Uytterhoeven
2016-06-29 18:12 ` Paul E. McKenney
2016-06-30 7:47 ` Joonsoo Kim
2016-06-30 7:58 ` Geert Uytterhoeven
2016-06-30 13:24 ` Paul E. McKenney
2016-06-30 13:31 ` Geert Uytterhoeven
2016-06-30 15:18 ` Paul E. McKenney
2016-06-30 15:53 ` Geert Uytterhoeven
2016-06-30 16:52 ` Paul E. McKenney
2016-06-30 17:54 ` Geert Uytterhoeven
2016-06-14 13:10 ` Geert Uytterhoeven
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