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

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Date:	Mon, 4 Feb 2013 19:28:33 +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

2013/2/4, Jan Kara <jack@...e.cz>:
> On Sat 02-02-13 15:21:09, Namjae Jeon wrote:
>> 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 ?
>   I had it in my tree but not in the for_next branch. Did it now so you
> should see the patch in tomorrow's linux-next.
Okay, I see.
Thanks Jan!
>
> 									Honza
>> 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
>> >>
>> >
> --
> Jan Kara <jack@...e.cz>
> SUSE Labs, CR
>
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