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

From: Namjae Jeon
Date: Sat Feb 02 2013 - 01:21:33 EST


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@xxxxxxxxx>:
> 2013/1/22, Jan Kara <jack@xxxxxxx>:
>> On Tue 22-01-13 09:45:09, Namjae Jeon wrote:
>>> 2013/1/21, Jan Kara <jack@xxxxxxx>:
>>> > @@ -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@xxxxxxx>
>> SUSE Labs, CR
>>
>
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/