From: Dimitri Sivanich <sivanich@sgi.com>
To: David Miller <davem@davemloft.net>
Cc: linux-kernel@vger.kernel.org, viro@ZenIV.linux.org.uk,
eric.dumazet@gmail.com, kuznet@ms2.inr.ac.ru, jmorris@namei.org,
yoshfuji@linux-ipv6.org, kaber@trash.net,
paulmck@linux.vnet.ibm.com, paul.gortmaker@windriver.com,
akpm@linux-foundation.org, jkosina@suse.cz, avi@redhat.com,
linux-fsdevel@vger.kernel.org, netdev@vger.kernel.org
Subject: Re: [PATCH] Fix panic in __d_lookup with high dentry hashtable counts
Date: Tue, 17 Jan 2012 11:41:26 -0600 [thread overview]
Message-ID: <20120117174126.GA18982@sgi.com> (raw)
In-Reply-To: <20120117.122229.323838457367599504.davem@davemloft.net>
On Tue, Jan 17, 2012 at 12:22:29PM -0500, David Miller wrote:
> From: Dimitri Sivanich <sivanich@sgi.com>
> Date: Tue, 17 Jan 2012 11:13:52 -0600
>
> > When the number of dentry cache hash table entries gets too high
> > (2147483648 entries), as happens by default on a 16TB system, use
> > of a signed integer in the dcache_init() initialization loop prevents
> > the dentry_hashtable from getting initialized, causing a panic in
> > __d_lookup().
> >
> > In addition, the _hash_mask returned from alloc_large_system_hash() does
> > not support more than a 32 bit hash table size.
> >
> > Changing the _hash_mask size returned from alloc_large_system_hash() to
> > support larger hash table sizes in the future, and changing loop counter
> > sizes appropriately.
> >
> > Signed-off-by: Dimitri Sivanich <sivanich@sgi.com>
>
> To be honest I think this is overkill.
I'm not going to flat-out disagree with you. These would be huge hash
tables. The thought was to make this __init code as flexible as possible.
>
> Supporting anything larger than a 32-bit hash mask is not even close
> to being reasonable. Nobody needs a 4GB hash table, not for anything.
Yes, at this point that is likely true.
>
> Instead I would just make sure everything is "unsigned int" or "u32"
> and calculations use things like "((u32) 1) << shift", and enforce an
> upper bounds of 0x80000000 or similar unconditionally in the hash
> allocator itself (rather than conditionally in the networking code).
OK. I had mentioned capping the value in alloc_large_system_hash() to
32 bits, but got no response to that proposal. I'll create a proper
patch.
>
> All of this "long" stuff is madness, what the heck is a long? It's a
> non-fixed type, yet you put constants in your code (0x80000000) which
> depend upon that type's size.
next prev parent reply other threads:[~2012-01-17 17:41 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-01-13 15:52 [PATCH] Fix panic in __d_lookup with high dentry hashtable counts Dimitri Sivanich
2012-01-13 16:15 ` Eric Dumazet
2012-01-13 16:22 ` Al Viro
2012-01-13 16:36 ` Dimitri Sivanich
2012-01-13 16:39 ` Dimitri Sivanich
2012-01-17 17:13 ` Dimitri Sivanich
2012-01-17 17:22 ` David Miller
2012-01-17 17:41 ` Dimitri Sivanich [this message]
2012-01-17 21:05 ` Dimitri Sivanich
2012-01-18 4:57 ` David Miller
2012-01-17 17:25 ` Al Viro
2012-01-17 17:28 ` David Miller
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