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Re: [PATCH] libxfs: increase hash chain depth when we run out of slots

To: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Subject: Re: [PATCH] libxfs: increase hash chain depth when we run out of slots
From: Eric Sandeen <sandeen@xxxxxxxxxxx>
Date: Thu, 17 Sep 2009 14:02:32 -0500
Cc: Eric Sandeen <sandeen@xxxxxxxxxx>, Tomek Kruszona <bloodyscarion@xxxxxxxxx>, Riku Paananen <riku.paananen@xxxxxxxxxxx>, xfs-oss <xfs@xxxxxxxxxxx>
In-reply-to: <20090917180931.GA21848@xxxxxxxxxxxxx>
References: <4AB25E78.8050001@xxxxxxxxxx> <20090917180931.GA21848@xxxxxxxxxxxxx>
User-agent: Thunderbird 2.0.0.21 (X11/20090320)
Christoph Hellwig wrote:
> On Thu, Sep 17, 2009 at 11:06:16AM -0500, Eric Sandeen wrote:
>> A couple people reported xfs_repair hangs after
>> "Traversing filesystem ..." in xfs_repair.  This happens
>> when all slots in the cache are full and referenced, and the
>> loop in cache_node_get() which tries to shake unused entries
>> fails to find any - it just keeps upping the priority and goes
>> forever.
>>
>> This can be worked around by restarting xfs_repair with
>> -P and/or "-o bhash=<largersize>" for older xfs_repair.
>>
>> I started down the path of increasing the number of hash buckets
>> on the fly, but Barry suggested simply increasing the max allowed
>> depth which is much simpler (thanks!)
>>
>> Resizing the hash lengths does mean that cache_report ends up with
>> most things in the "greater-than" category:
>>
>> ...
>> Hash buckets with  23 entries      3 (  3%)
>> Hash buckets with  24 entries      3 (  3%)
>> Hash buckets with >24 entries     50 ( 85%)
>>
>> but I think I'll save that fix for another patch unless there's
>> real concern right now.
>>
>> I tested this on the metadump image provided by Tomek.
> 
> How large is that image?  I really think we need to start collecting
> these images for regression testing.

zipped metadump is 170M; unzipped 1.1G.

Crafting a special test fs somehow might be better; maybe with an
artificially low bhashsize or something ....  yeah, I know.  I'm not
sure how to manage the regression testing.  Working backwards to a
minimal testcase on these would be extremely time-consuming and/or
impossible I'm afraid.

> The patch looks good to me,

thanks for the review

-Eric

> 
> Reviewed-by: Christoph Hellwig <hch@xxxxxx>
> 
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