linux-kernel - Re: [PATCH] udf: add extent cache support in case of file reading

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Date:	Sat, 2 Feb 2013 15:21:09 +0900
From:	Namjae Jeon <linkinjeon@...il.com>
To:	Jan Kara <jack@...e.cz>
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	Namjae Jeon <namjae.jeon@...sung.com>,
	Ashish Sangwan <a.sangwan@...sung.com>,
	Bonggil Bak <bgbak@...sung.com>
Subject: Re: [PATCH] udf: add extent cache support in case of file reading

Hi. Jan.

Sorry for interrupt.
Have you taken this patch to your tree ? I can not find it..
or Is there any issue regarding this patch ?

Thanks!

2013/1/22, Namjae Jeon <linkinjeon@...il.com>:
> 2013/1/22, Jan Kara <jack@...e.cz>:
>> On Tue 22-01-13 09:45:09, Namjae Jeon wrote:
>>> 2013/1/21, Jan Kara <jack@...e.cz>:
>>> > @@ -2222,6 +2219,8 @@ int udf_read_extent_cache(struct inode *inode,
>>> > loff_t
>>> > bcount,
>>> >  		*lbcount = iinfo->cached_extent.lstart;
>>> >  		memcpy(pos, &iinfo->cached_extent.epos,
>>> >  		       sizeof(struct extent_position));
>>> > +		if (pos->bh)
>>> > +			get_bh(pos->bh);
>>> >  		spin_unlock(&iinfo->i_extent_cache_lock);
>>> >  		return 1;
>>> >  	} else
>>> >   This is the most important - we should give buffer reference to
>>> > pos->bh.
>>> > Caller will eventually free it right?
>>> This change is not required as we give buffer reference to pos->bh at
>>> the time of cache update.
>>> When we start reading a file, first we try to read the cache which
>>> will lead to cache miss.
>>> So, we would really access the pos->bh in udf_update_extent_cache for
>>> the first time, and this is where the buffer reference is incremented.
>>> Calling get_bh at 2 places will eventually lead to mem leak.
>>> Let me know your opinion.
>>   Yes, udf_update_extent_cache() gets its own reference to bh but that is
>> dropped in udf_clear_extent_cache(). So I think udf_read_extent_cache()
>> needs to get a reference to the caller (as the caller will eventually
>> free
>> the bh via brelse(epos.bh) e.g. in udf_extend_file(). Also I realized
>> udf_update_extent_cache() needs to first clear the cache if it is valid.
>> Otherwise it just overwrites bh pointer and reference is leaked. Is it
>> clearer now?
> Yes, you're right. Also, this patch looks good to me.
>>
>>   I've also changed locking of udf_clear_extent_cache() so that
>> i_extent_cache_lock is always taken for that function - it makes the
>> locking rules obvious at the first sight.
> Yes, right. it is needed.
> When we test with this patch, working fine.
> Thanks Jan!
>>
>>   Attached is the patch I currently carry.
>>
>> 								Honza
>>
>> --
>> Jan Kara <jack@...e.cz>
>> SUSE Labs, CR
>>
>
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