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From: Nikita Danilov <Nikita@Namesys.COM>
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Date: Thu, 31 Oct 2002 20:04:40 +0300
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To: Christoph Hellwig <hch@infradead.org>
Cc: Linus Torvalds <Torvalds@Transmeta.COM>,
       Linux Kernel Mailing List <Linux-Kernel@Vger.Kernel.ORG>
Subject: Re: [PATCH]: reiser4 [5/8] export remove_from_page_cache()
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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.
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