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

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Date:	Tue, 20 Feb 2007 13:59:59 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Andrew Morton <akpm@...l.org>
Cc:	Christoph Lameter <clameter@....com>,
	Trond Myklebust <trond.myklebust@....uio.no>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org, pj@....com
Subject: Re: [PATCH] nfs: fix congestion control -v4

On Fri, 2007-01-26 at 00:51 -0800, Andrew Morton wrote:
> On Fri, 26 Jan 2007 09:03:37 +0100
> Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
> 
> > On Thu, 2007-01-25 at 22:04 -0800, Andrew Morton wrote:
> > > On Thu, 25 Jan 2007 21:31:43 -0800 (PST)
> > > Christoph Lameter <clameter@....com> wrote:
> > > 
> > > > On Thu, 25 Jan 2007, Andrew Morton wrote:
> > > > 
> > > > > atomic_t is 32-bit.  Put 16TB of memory under writeback and blam.
> > > > 
> > > > We have systems with 8TB main memory and are able to get to 16TB.
> > > 
> > > But I bet you don't use 4k pages on 'em ;)
> > > 
> > > > Better change it now.
> > > 
> > > yup.
> > 
> > I can change to atomic_long_t but that would make this patch depend on
> > Mathieu Desnoyers' atomic.h patch series.

    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

> > Do I send out a -v5 with this, or should I send an incremental patch
> > once that hits your tree?
> 
> A patch against next -mm would suit, thanks.


As promised change the atomic_t in struct nfs_server to atomic_long_t in
anticipation of machines that can handle 8+TB of (4K) pages under writeback.

However I suspect other things in NFS will start going *bang* by then.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
---
 fs/nfs/write.c            |    4 ++--
 include/linux/nfs_fs_sb.h |    2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

Index: linux-2.6/fs/nfs/write.c
===================================================================
--- linux-2.6.orig/fs/nfs/write.c
+++ linux-2.6/fs/nfs/write.c
@@ -224,7 +224,7 @@ static void nfs_set_page_writeback(struc
 		struct inode *inode = page->mapping->host;
 		struct nfs_server *nfss = NFS_SERVER(inode);
 
-		if (atomic_inc_return(&nfss->writeback) >
+		if (atomic_long_inc_return(&nfss->writeback) >
 				NFS_CONGESTION_ON_THRESH)
 			set_bdi_congested(&nfss->backing_dev_info, WRITE);
 	}
@@ -236,7 +236,7 @@ static void nfs_end_page_writeback(struc
 	struct nfs_server *nfss = NFS_SERVER(inode);
 
 	end_page_writeback(page);
-	if (atomic_dec_return(&nfss->writeback) < NFS_CONGESTION_OFF_THRESH) {
+	if (atomic_long_dec_return(&nfss->writeback) < NFS_CONGESTION_OFF_THRESH) {
 		clear_bdi_congested(&nfss->backing_dev_info, WRITE);
 		congestion_end(WRITE);
 	}
Index: linux-2.6/include/linux/nfs_fs_sb.h
===================================================================
--- linux-2.6.orig/include/linux/nfs_fs_sb.h
+++ linux-2.6/include/linux/nfs_fs_sb.h
@@ -82,7 +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 */
+	atomic_long_t		writeback;	/* number of writeback pages */
 	int			flags;		/* various flags */
 	unsigned int		caps;		/* server capabilities */
 	unsigned int		rsize;		/* read size */


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