Re: [PATCH]: reiser4 [5/8] export remove_from_page_cache()

[Nikita Danilov]

Andreas Dilger writes:
 > On Oct 31, 2002  16:31 +0000, Christoph Hellwig wrote:
 > > On Thu, Oct 31, 2002 at 07:24:40PM +0300, Nikita Danilov wrote:
 > > > Reiser4 stores meta-data in a huge balanced tree. This tree is kept
 > > > (partially) in the page cache. All pages in this tree are attached to
 > > > "fake" inode. Sometimes you need to remove node from the tree. At this
 > > > moment page has to be removed from the fake inode mapping.
 > > 
 > > What about chaing truncate_inode_pages to take an additional len
 > > argument so you don't have to remove all pages past an offset?
 > 
 > That would be what we have been calling "punch", and is quite useful
 > for putting holes in files (i.e. making them sparse again).  This
 > can be used for InterMezzo (among other things) so that the KML log
 > file can be growing at the end, but being punched out at the start
 > so it doesn't use up a lot of disk space.

Abusing truncate for such things will remain abuse exactly. Separate
interface is required.

 > 
 > Not that I'm holding my breath on getting this in the kernel, but
 > it is definitely useful.
 > 
 > Cheers, Andreas

Nikita.