Subject: Re: filesystem read-ahead caching....
To: NetBSD Kernel Technical Discussion List <tech-kern@NetBSD.ORG>
From: Greg A. Woods <>
List: tech-kern
Date: 05/03/2001 23:57:03
[ On Thursday, May 3, 2001 at 20:53:58 (-0700), Chuck Silvers wrote: ]
> Subject: Re: filesystem read-ahead caching....
> all of the filesystems now do read ahead and write behind with clustering.
> the cluster_{read,write}() code is not used anymore since that code deals
> with the buffer cache and regular file data is no longer stored in the
> buffer cache.  for read ahead, look in genfs_getpages() where it calls
> VOP_GETPAGES() recursively.
> LFS will be converted to use the page cache for file data as well once
> I finish with the code I'm working on now to enable that.  so far I'm
> still working on implementing pmap_{kenter_pa,kremove} in more pmaps
> (since that is required by my new code), but hopefully I'll get to
> LFS before too much longer.  once LFS is converted, vfs_cluster.c
> can be deleted since it won't be used anymore.

Ah ha!  Thanks very much for the explanation!

I was being confused by trailing dregs and not seeing the new scheme...

Am I right in assuming that this comment from genfs_vnops.c indicates
the current state of affairs w.r.t. controlling the amount of

         * XXXUBC for now, just read the next 128k on 64k boundaries.
         * this is pretty nonsensical, but it is 50% faster than reading
         * just the next 64k.

							Greg A. Woods

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