On Sat, Apr 20, 2013 at 03:42:41PM +0200, Jan Kara wrote:
> On Tue 09-04-13 11:14:26, Lukas Czerner wrote:
> > Currently punch hole is disabled in file systems with bigalloc
> > feature enabled. However the recent changes in punch hole patch should
> > make it easier to support punching holes on bigalloc enabled file
> > systems.
> >
> > This commit changes partial_cluster handling in ext4_remove_blocks(),
> > ext4_ext_rm_leaf() and ext4_ext_remove_space(). Currently
> > partial_cluster is unsigned long long type and it makes sure that we
> > will free the partial cluster if all extents has been released from that
> > cluster. However it has been specifically designed only for truncate.
> >
> > With punch hole we can be freeing just some extents in the cluster
> > leaving the rest untouched. So we have to make sure that we will notice
> > cluster which still has some extents. To do this I've changed
> > partial_cluster to be signed long long type. The only scenario where
> > this could be a problem is when cluster_size == block size, however in
> > that case there would not be any partial clusters so we're safe. For
> > bigger clusters the signed type is enough. Now we use the negative value
> > in partial_cluster to mark such cluster used, hence we know that we must
> > not free it even if all other extents has been freed from such cluster.
> >
> > This scenario can be described in simple diagram:
> >
> > |FFF...FF..FF.UUU|
> > ^----------^
> > punch hole
> >
> > . - free space
> > | - cluster boundary
> > F - freed extent
> > U - used extent
> >
> > Also update respective tracepoints to use signed long long type for
> > partial_cluster.
> The patch looks OK. You can add:
> Reviewed-by: Jan Kara <jack@xxxxxxx>
>
> Just a minor nit - sometimes you use 'signed long long', sometimes 'long
> long int', sometimes just 'long long'. In kernel we tend to always use just
> 'long long' so it would be good to clean that up.
Another question is that in patch 01/18 invalidatepage signature is
changed from
int (*invalidatepage) (struct page *, unsigned long);
to
void (*invalidatepage) (struct page *, unsigned int, unsigned int);
The argument type is changed from 'unsigned long' to 'unsigned int'. My
question is why we need to change it.
Thanks,
- Zheng
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