netdev - Re: [PATCH] Fix panic in __d_lookup with high dentry hashtable counts

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Date:	Tue, 17 Jan 2012 12:28:00 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	viro@...IV.linux.org.uk
Cc:	sivanich@....com, linux-kernel@...r.kernel.org,
	eric.dumazet@...il.com, kuznet@....inr.ac.ru, jmorris@...ei.org,
	yoshfuji@...ux-ipv6.org, kaber@...sh.net,
	paulmck@...ux.vnet.ibm.com, paul.gortmaker@...driver.com,
	akpm@...ux-foundation.org, jkosina@...e.cz, avi@...hat.com,
	linux-fsdevel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH] Fix panic in __d_lookup with high dentry hashtable
 counts

From: Al Viro <viro@...IV.linux.org.uk>
Date: Tue, 17 Jan 2012 17:25:27 +0000

> On Tue, Jan 17, 2012 at 11:13:52AM -0600, Dimitri Sivanich wrote:
>> 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.
> 
> ... and I still would like to see somebody familiar with uses of other
> hashes to comment on the desirability of such monsters.  For dcache and
> icache it's absolutely certain to be worse than useless.  We are talking
> about 4Gbuckets here...

It's wrong in networking too.
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