fs/udf: vm pages "overlap" while reading large dir [patch]

[Scott Long]

Andriy Gapon wrote:
> on 04/02/2008 22:07 Pav Lucistnik said the following:
>> Julian Elischer píše v po 04. 02. 2008 v 10:36 -0800:
>>> Andriy Gapon wrote:
>>>> More on the problem with reading big directories on UDF.
>>> You do realise that you have now made yourself the official
>>> maintainer of the UDF file system by submitting a competent
>>> and insightful analysis of the problem?
>> Yay, and can you fix the sequential read performance while you're at it?
>> Kthx!
>>
> 
> Pav,
> 
> this was almost trivial :-)
> See the attached patch, first hunk is just for consistency.
> The code was borrowed from cd9660, only field/variable names are adjusted.
> 

Your patch looks reasonable.  Btw, for the same reason that read-ahead
makes file reading much faster, I would not change directory reading to
be 1 sector at a time (unless you also do read-ahead for it).

> But there is another issue that I also mentioned in the email about
> directory reading. It is UDF_INVALID_BMAP case of udf_bmap_internal,
> i.e. the case when file data is embedded into a file entry.
> This is a special case that needs to be handled differently.
> udf_readatoffset() handles it, but the latest udf_read code doesn't.
> I have a real UDF filesystem where this type of allocation is used for
> small files and those files can not be read.

Oh, so directory data can also follow this convention?  Blah.  Feel free
to fix that too if you want =-)

Scott