Messages in this thread |  | | Date | Tue, 7 Jan 1997 09:46:00 +0100 (MET) | From | Ingo Molnar <> | Subject | Re: Suggestion for Linux 2.3 |
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On Mon, 6 Jan 1997, David S. Miller wrote:
> Date: Mon, 6 Jan 1997 17:23:01 -0600 (CST) > From: "Daniel G. Linder" <dlinder@webcentric.net> > > Anyone want to work on this for Linux? I don't have the time to be > a lead person, but this looks like it would integrate well with the > MD driver (Multi Disk)... Might be a big step for ext2 -- anything > going on with that project? > > I would like to see full logging and journaling added to ext2 before > we allow such a scheme.
part of our RAID1, RAID4 and RAID5 code [we've announced it not so long ago on linux-raid] are kernel system threads that do nontrivial/abstract IO operations like RAID5 writes (which are a series of coordinated IO operations) or RAID5 error recovery [redirecting and retrying IO requests]. Once we have implemented this in a sufficiently clean way [the Linux way of caching VM and blocks is affected], journal or transaction based filesystems should be a breeze :)
The only open issue here is the dualness of Linux caching: on one side an (inode,offset) based page cache, and a (dev,blocknr) block cache. Cache elements in the VM cache do not show up in the block cache. Since any nontrivial IO system like the RAID stuff is not only a 'block provider' but a 'block requester' too, we have to do all things twice all things twice. [for example, first we have to look wether a cache element is in the page cache, then in the block cache ... yuck imho]
What we need for this particular application is a 'uniform cache interface'. Or the total extinction of the buffer cache (which is imho not possible due to other VM-neutral physical blocks like superblocks or filesystem metadata in general).
somehow it would be cool to have the VM cache folded into the buffer cache ... without extra overhead ... [asking the impossible :)] ... thus we could query the buffer cache for everything.
just have thrown in the problem here, maybe you guys have already ideas lying around :)
-- mingo
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