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From: Nikita Danilov <Nikita@Namesys.COM>
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Date: Thu, 31 Oct 2002 21:25:24 +0300
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To: Andreas Dilger <adilger@clusterfs.com>
Cc: Christoph Hellwig <hch@infradead.org>,
       Linus Torvalds <Torvalds@Transmeta.COM>,
       Linux Kernel Mailing List <Linux-Kernel@Vger.Kernel.ORG>,
       Reiserfs mail-list <Reiserfs-List@Namesys.COM>
Subject: Re: [PATCH]: reiser4 [5/8] export remove_from_page_cache()
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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.
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