Date:   Thu, 20 Dec 2018 15:13:08 -0500
From:   Bruce Fields <bfields@fieldses.org>
To:     Chuck Lever <chuck.lever@oracle.com>
Cc:     Trond Myklebust <trondmy@hammerspace.com>,
        Anna Schumaker <schumakeranna@gmail.com>,
        Linux NFS Mailing List <linux-nfs@vger.kernel.org>
Subject: Re: [PATCH] sunrpc: convert unnecessary GFP_ATOMIC to GFP_NOFS
Message-ID: <20181220201308.GA8466@fieldses.org>
References: <20181220153511.GB6063@fieldses.org>
 <20181220154236.GC6063@fieldses.org>
 <09BE8CC3-B528-45BA-B10E-01D7F9FD264D@oracle.com>
 <20181220155219.GD6063@fieldses.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20181220155219.GD6063@fieldses.org>
User-Agent: Mutt/1.5.21 (2010-09-15)
Sender: linux-nfs-owner@vger.kernel.org
Precedence: bulk

On Thu, Dec 20, 2018 at 10:52:19AM -0500, Bruce Fields wrote:
> On Thu, Dec 20, 2018 at 10:47:25AM -0500, Chuck Lever wrote:
> > 
> > 
> > > 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"
> 
> Oops, thanks.

(Trond or Anna, I'm assuming you can fix that up, but let me know if
you'd rather I resent.)

--b.

> 
> > > 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.
> 
> Yeah, just noting it for future reference.
> 
> --b.
> 
> > > 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
> > 
> >