Re: [PATCH] nfs: fix congestion control -v4

[Andrew Morton <akpm@osdl.org>]

On Thu, 25 Jan 2007 16:32:28 +0100
Peter Zijlstra <a.p.zijlstra@chello.nl> wrote:

> Hopefully the last version ;-)
> 
> 
> ---
> Subject: nfs: fix congestion control
> 
> The current NFS client congestion logic is severly broken, it marks the backing
> device congested during each nfs_writepages() call but doesn't mirror this in
> nfs_writepage() which makes for deadlocks. Also it implements its own waitqueue.
> 
> Replace this by a more regular congestion implementation that puts a cap on the
> number of active writeback pages and uses the bdi congestion waitqueue.
> 
> Also always use an interruptible wait since it makes sense to be able to 
> SIGKILL the process even for mounts without 'intr'.
> 
> ..
>
> --- linux-2.6-git.orig/include/linux/nfs_fs_sb.h	2007-01-25 16:07:03.000000000 +0100
> +++ linux-2.6-git/include/linux/nfs_fs_sb.h	2007-01-25 16:07:12.000000000 +0100
> @@ -82,6 +82,7 @@ struct nfs_server {
>  	struct rpc_clnt *	client_acl;	/* ACL RPC client handle */
>  	struct nfs_iostats *	io_stats;	/* I/O statistics */
>  	struct backing_dev_info	backing_dev_info;
> +	atomic_t		writeback;	/* number of writeback pages */

We're going to get in trouble with this sort of thing within a few years. 
atomic_t is 32-bit.  Put 16TB of memory under writeback and blam.