linux-kernel - Re: [PATCH][RFC]fix soft lock up at NFS mount by per-SB LRU-list of unused dentries

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Message-ID: <483628B7.1080704@np.css.fujitsu.com>
Date:	Fri, 23 May 2008 11:15:19 +0900
From:	Kentaro Makita <k-makita@...css.fujitsu.com>
To:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Cc:	akpm@...ux-foundation.org, dgc@....com, viro@...IV.linux.org.uk,
	harvey.harrison@...il.com
Subject: Re: [PATCH][RFC]fix soft lock up at NFS mount by per-SB LRU-list
 of unused dentries

Hi, David

Thank you for reviewing the patch.
I'd fix coding style issues at next post. And,...

David Chinner wrote:
> On Thu, May 22, 2008 at 11:22:18AM +0900, Kentaro Makita wrote:
>> +			}
>> +		}
>> +	}
> 
> I'm wondering if this loop is an excessively long time to be holding the
> dcache_lock. I guess the hol dtime is limited by the size of *count being
> passed in. I think we could also do a:
> 
> 		cond_resched_lock(&dcache_lock);
> 	
> in the loop here to prevent this from occurring....
Did you mean:
 - scan sb->s_dentry_lru and move dentries to temporary list
   with lock held
 - cond_resched_lock(&dcache_lock);
 - prune dentries on temporary list
Is that right?

....
>> +	spin_lock(&sb_lock);
>> +	list_for_each_entry(sb, &super_blocks, s_list) {
> 
> Question on lock ordering of sb_lock vs dcache_lock - which is the inner
> lock? Are the two of them held together anywhere else? (/me doesn't
> have time to searchthe code right now).
> 
The sb_lock is inner lock. And I searched the whole code and found only
 prune_dcache() held both sb_lock and dcache_lock.

Best Regards,
Kentaro Makita
> 
> Otherwise it's looking good.
> 
> Cheers,
> 
> Dave.
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