Messages in this thread | | | Date | Mon, 17 Dec 2001 14:49:29 +1100 | From | David Gibson <> | Subject | Re: question about kernel 2.4 ramdisk |
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On Sun, Dec 16, 2001 at 04:34:01PM +0100, Christoph Rohland wrote: > Hi David, > > On Fri, 14 Dec 2001, David Gibson wrote: > >> But the core of shmem is always compiled. And the rest is as simple > >> as ramfs... > > > > The point of keeping ramfs simple isn't to reduce the kernel image > > size, it's to keep it useful as an example of how to make a trivial > > filesystem. > > >From this point of view I prefer the oversimplified version in the > stock kernel. We should probably correct the comment about missing > features like limits and timestamps and tag it as experimental. But > IMHO this version explains the underlying concept best. > > > If we want a useable ramfs implementation we should try to keep the > image size down and try to make it as similar to tmpfs as > possible. This would keep the administrators overhead low. > > I append two cummulative patches against 2.4.17-rc1 (only slightly > tested): > > 1) Add removepage to the addresspace_operations to simplify > shmem.c. This is taken from your ramfs limits patch. > 2) Add support for a ramfs2 filesystem type to shmem.c. The only > feature missing compared to ramfs + limits are loopback devices on > top of ramfs files. It does not add memory need compared to > ramfs. Have a look how small this is.
I don't think there's a lot of point playing with this in 2.4.x. In 2.5 it depends a bit on what changes to the VFS happen. I recall that near the end of the 2.3 cycle Al Viro proposed a change to add essentially a removepage operation (he called it detachpage IIRC) - he was using it to eliminate a bunch of the "if (page->buffers)" tests. I don't know it that's still on the cards - it so it could certainly simplify both ramfs and shmfs.
-- David Gibson | For every complex problem there is a david@gibson.dropbear.id.au | solution which is simple, neat and | wrong. -- H.L. Mencken http://www.ozlabs.org/people/dgibson
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