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

[Nikita Danilov <Nikita@Namesys.COM>]

Christoph Hellwig writes:
 > On Thu, Oct 31, 2002 at 07:45:39PM +0300, Nikita Danilov wrote:
 > > Interesting. Then, XFS and JFS meta data in the page cache probably
 > > are linearly ordered, and there it is never necessary to remove meta
 > > data page from the middle of the mapping, right?
 > 
 > The issue is rather different for XFS and JFS.  in JFS most metadata
 > (actually all metadata but the small superblock) is stored in inodes,
 > and it's accessed through the pagecache mapping for those inodes.
 > 
 > All access to those pages doesn't go directly through the pagecache
 > interface but a small metapage wrapper.  When the page is removed it's synced
 > to disk and removed from the metapage hash, so that you can't acess it
 > anymore.  It might still be on the VM lists for a while.

Interesting. But things like ->vm_writeback() and friends will go
directly to the page bypassing metapage wrapper, right? JFS checks that
page is still "live" on each low-level VM call?

 > 
 > XFS on the other hand only uses the blockdevice mapping to acess it's
 > metadata so it doesn't have to remove the page explicitly from the
 > cache ever.
 > 

Nikita.