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Subject: Re: [PATCH] sunrpc: convert unnecessary GFP_ATOMIC to GFP_NOFS
From:   Chuck Lever <chuck.lever@oracle.com>
In-Reply-To: <20181220154236.GC6063@fieldses.org>
Date:   Thu, 20 Dec 2018 10:47:25 -0500
Cc:     Trond Myklebust <trondmy@hammerspace.com>,
        Anna Schumaker <schumakeranna@gmail.com>,
        Linux NFS Mailing List <linux-nfs@vger.kernel.org>
Content-Transfer-Encoding: 7bit
Message-Id: <09BE8CC3-B528-45BA-B10E-01D7F9FD264D@oracle.com>
References: <20181220153511.GB6063@fieldses.org>
 <20181220154236.GC6063@fieldses.org>
To:     Bruce Fields <bfields@fieldses.org>
Sender: linux-nfs-owner@vger.kernel.org
Precedence: bulk


> On Dec 20, 2018, at 10:42 AM, J. Bruce Fields <bfields@fieldses.org> wrote:
> 
> From: "J. Bruce Fields" <bfields@redhat.com>
> 
> It's OK to sleep here, we just don't want to recurse into the filesystem
> as this writeout could be waiting on this.

"as a writeout"


> Future work: the documentation for GFP_NOFS says "Please try to avoid
> using this flag directly and instead use memalloc_nofs_{save,restore} to
> mark the whole scope which cannot/shouldn't recurse into the FS layer
> with a short explanation why. All allocation requests will inherit
> GFP_NOFS implicitly."
> 
> But I'm not sure where to do this.  Should the workqueue be arranging
> that for us in the case of workqueues created with WQ_MEM_RECLAIM?

There seem to be plenty of uses of GFP_NOFS in NFS and sunrpc.
That sounds like a big project.


> Reported-by: Trond Myklebust <trondmy@hammer.space>
> Signed-off-by: J. Bruce Fields <bfields@redhat.com>
> ---
> net/sunrpc/rpcb_clnt.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
> 
> Also, I've still got this one.  (And still haven't looked into whether
> it should be using a memalloc_nofs_{save,restore} elsewhere instead.)
> 
> diff --git a/net/sunrpc/rpcb_clnt.c b/net/sunrpc/rpcb_clnt.c
> index 08b5fa4a2852..41a971ac1c63 100644
> --- a/net/sunrpc/rpcb_clnt.c
> +++ b/net/sunrpc/rpcb_clnt.c
> @@ -752,7 +752,7 @@ void rpcb_getport_async(struct rpc_task *task)
> 		goto bailout_nofree;
> 	}
> 
> -	map = kzalloc(sizeof(struct rpcbind_args), GFP_ATOMIC);
> +	map = kzalloc(sizeof(struct rpcbind_args), GFP_NOFS);
> 	if (!map) {
> 		status = -ENOMEM;
> 		dprintk("RPC: %5u %s: no memory available\n",
> @@ -770,7 +770,7 @@ void rpcb_getport_async(struct rpc_task *task)
> 	case RPCBVERS_4:
> 	case RPCBVERS_3:
> 		map->r_netid = xprt->address_strings[RPC_DISPLAY_NETID];
> -		map->r_addr = rpc_sockaddr2uaddr(sap, GFP_ATOMIC);
> +		map->r_addr = rpc_sockaddr2uaddr(sap, GFP_NOFS);
> 		if (!map->r_addr) {
> 			status = -ENOMEM;
> 			dprintk("RPC: %5u %s: no memory available\n",
> -- 
> 2.19.2
> 

--
Chuck Lever