On Thu, 25 Jan 2007 16:32:28 +0100
Peter Zijlstra <[EMAIL PROTECTED]> 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.

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