Re: CONFIG_DEBUG_SLAB_LEAK omits size-4096 and larger?

["J. Bruce Fields" <bfields@fieldses.org>]

On Thu, Jun 12, 2008 at 02:54:09PM -0500, Weathers, Norman R. wrote:
>  
> 
> > -----Original Message-----
> > From: linux-nfs-owner@vger.kernel.org 
> > [mailto:linux-nfs-owner@vger.kernel.org] On Behalf Of J. Bruce Fields
> > Sent: Wednesday, June 11, 2008 5:55 PM
> > To: Weathers, Norman R.
> > Cc: Jeff Layton; linux-kernel@vger.kernel.org; 
> > linux-nfs@vger.kernel.org
> > Subject: Re: CONFIG_DEBUG_SLAB_LEAK omits size-4096 and larger?
> > 
> > On Wed, Jun 11, 2008 at 05:46:13PM -0500, Weathers, Norman R. wrote:
> > > I will try and get it patched and retested, but it may be a 
> > day or two
> > > before I can get back the information due to production jobs now
> > > running.  Once they finish up, I will get back with the info.
> > 
> > Understood.
> > 
> 
> 
> I was able to get my big user to cooperate and let me in to be able to
> get the information that you were needing.  The full output from the
> /proc/slab_allocator file is at
> http://www.shashi-weathers.net/linux/cluster/NFS_DEBUG_2 .  The 16
> thread case is very interesting.  Also, there is a small txt file in the
> directory that has some rpc errors, but I imagine the way that I am
> running the box (oversubscribed threads) has more to do with the rpc
> errors than anything else.  For those of you wanting the gist of the
> story, the size-4096 slab has the following very large allocation:
> 
> size-4096: 2 sys_init_module+0x140b/0x1980
> size-4096: 1 __vmalloc_area_node+0x188/0x1b0
> size-4096: 1 seq_read+0x1d9/0x2e0
> size-4096: 1 slabstats_open+0x2b/0x80
> size-4096: 5 vc_allocate+0x167/0x190
> size-4096: 3 input_allocate_device+0x12/0x80
> size-4096: 1 hid_add_field+0x122/0x290
> size-4096: 9 reqsk_queue_alloc+0x5f/0xf0
> size-4096: 1846825 __alloc_skb+0x7d/0x170
> size-4096: 3 alloc_netdev+0x33/0xa0
> size-4096: 10 neigh_sysctl_register+0x52/0x2b0
> size-4096: 5 devinet_sysctl_register+0x28/0x110
> size-4096: 1 pidmap_init+0x15/0x60
> size-4096: 1 netlink_proto_init+0x44/0x190
> size-4096: 1 ip_rt_init+0xfd/0x2f0
> size-4096: 1 cipso_v4_init+0x13/0x70
> size-4096: 3 journal_init_revoke+0xe7/0x270 [jbd]
> size-4096: 3 journal_init_revoke+0x18a/0x270 [jbd]
> size-4096: 2 journal_init_inode+0x84/0x150 [jbd]
> size-4096: 2 bnx2_alloc_mem+0x18/0x1f0 [bnx2]
> size-4096: 1 joydev_connect+0x53/0x390 [joydev]
> size-4096: 13 kmem_alloc+0xb3/0x100 [xfs]
> size-4096: 5 addrconf_sysctl_register+0x31/0x130 [ipv6]
> size-4096: 7 rpc_clone_client+0x84/0x140 [sunrpc]
> size-4096: 3 rpc_create+0x254/0x4d0 [sunrpc]
> size-4096: 16 __svc_create_thread+0x53/0x1f0 [sunrpc]
> size-4096: 16 __svc_create_thread+0x72/0x1f0 [sunrpc]
> size-4096: 1 nfsd_racache_init+0x2e/0x140 [nfsd]
> 
> The big one seems to be the __alloc_skb. (This is with 16 threads, and
> it says that we are using up somewhere between 12 and 14 GB of memory,
> about 2 to 3 gig of that is disk cache).  If I were to put anymore
> threads out there, the server would become almost unresponsive (it was
> bad enough as it was).   
> 
> At the same time, I also noticed this:
> 
> skbuff_fclone_cache: 1842524 __alloc_skb+0x50/0x170
> 
> Don't know for sure if that is meaningful or not....

OK, so, starting at net/core/skbuff.c, this means that this memory was
allocated by __alloc_skb() calls with something nonzero in the third
("fclone") argument.  The only such caller is alloc_skb_fclone().
Callers of alloc_skb_fclone() include:

	sk_stream_alloc_skb:
		do_tcp_sendpages
		tcp_sendmsg
		tcp_fragment
		tso_fragment
		tcp_mtu_probe
	tcp_send_fin
	tcp_connect
	buf_acquire:
		lots of callers in tipc code (whatever that is).

So unless you're using tipc, or you have something in userspace going
haywire (perhaps netstat would help rule that out?), then I suppose
there's something wrong with knfsd's tcp code.  Which makes sense, I
guess.

I'd think this sort of allocation would be limited by the number of
sockets times the size of the send and receive buffers.
svc_xprt.c:svc_check_conn_limits() claims to be limiting the number of
sockets to (nrthreads+3)*20.  (You aren't hitting the "too many open
connections" printk there, are you?)  The total buffer size should be
bounded by something like 4 megs.

--b.

> 
> 
> 
> > > Thanks everyone for looking at this, by the way!
> > 
> > And thanks for your persistence.
> > 
> > --b.
> > 
> 
> 
> Anytime.  This is the part of the job that is fun (except for my
> users...).  Anyone can watch a system run, it's dealing with the unknown
> that makes it interesting.

OK!  Because I'm a bit stuck, so this will take some more work....

--b.

> 
> 
> Norman Weathers
> 
> 
> > > 
> > > > 
> > > > 
> > > > diff --git a/mm/slab.c b/mm/slab.c
> > > > index 06236e4..b379e31 100644
> > > > --- a/mm/slab.c
> > > > +++ b/mm/slab.c
> > > > @@ -2202,7 +2202,7 @@ kmem_cache_create (const char *name, 
> > > > size_t size, size_t align,
> > > >  	 * above the next power of two: caches with object 
> > > > sizes just above a
> > > >  	 * power of two have a significant amount of internal 
> > > > fragmentation.
> > > >  	 */
> > > > -	if (size < 4096 || fls(size - 1) == fls(size-1 + REDZONE_ALIGN +
> > > > +	if (size < 8192 || fls(size - 1) == fls(size-1 + REDZONE_ALIGN +
> > > >  						2 * 
> > > > sizeof(unsigned long long)))
> > > >  		flags |= SLAB_RED_ZONE | SLAB_STORE_USER;
> > > >  	if (!(flags & SLAB_DESTROY_BY_RCU))
> > > > 
> > > 
> > > 
> > > Norman Weathers
> > --
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