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Date: Tue, 31 Jul 2012 18:50:22 +0100
From: Mel Gorman <mgorman@...e.de>
To: "Myklebust, Trond" <Trond.Myklebust@...app.com>,
Andrew Morton <akpm@...ux-foundation.org>
Cc: Stephen Rothwell <sfr@...b.auug.org.au>,
"linux-next@...r.kernel.org" <linux-next@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Jeff Layton <jlayton@...hat.com>
Subject: Re: linux-next: manual merge of the akpm tree with the nfs tree
On Tue, Jul 31, 2012 at 03:35:07PM +0000, Myklebust, Trond wrote:
> On Tue, 2012-07-31 at 16:19 +0100, Mel Gorman wrote:
> > On Tue, Jul 31, 2012 at 02:37:24PM +0000, Myklebust, Trond wrote:
> > > On Tue, 2012-07-31 at 11:33 +0100, Mel Gorman wrote:
> > > > On Tue, Jul 31, 2012 at 02:24:41PM +1000, Stephen Rothwell wrote:
> > > > > Hi Andrew,
> > > > >
> > > > > Today's linux-next merge of the akpm tree got a conflict in
> > > > > net/sunrpc/xprtsock.c between commit 5cf02d09b50b ("nfs: skip commit in
> > > > > releasepage if we're freeing memory for fs-related reasons") from the nfs
> > > > > tree and commit "nfs: enable swap on NFS" from the akpm tree.
> > > > >
> > > > > Just context changes? I fixed it up (I think - see below) and can carry
> > > > > the fix as necessary.
> > > >
> > > > Functionally it looks fine. As you say, it all looks like context
> > > > changes. Arguably code like this
> > > >
> > > > current->flags &= ~PF_FSTRANS
> > > >
> > > > could use tsk_restore_flags instead() even though it should never be
> > > > necessary as PF_FSTRANS would not be set on function entry. However,
> > > > it would set up a depedency between the patch sets that is undesirable.
> > > > If both sets get merged then it might make sense as a cleanup to use
> > > > tsk_restore_flags() but not until then.
> > > >
> > > > Thanks Stephen.
> > > >
> > >
> > > Do we really need to set both PF_FSTRANS and PF_MEMALLOC here? The
> > > reason why I merged the PF_FSTRANS patch is that we have the deadlock
> > > problem when allocating a new socket even before we add swap-over-nfs.
> > > Adding PF_FSTRANS to disallow entry into the NFS layer by the memory
> > > allocator fixes that issue.
> >
> > PF_FSTRANS is to prevent recursion into NFS and is set whether swap-over-NFS
> > is used or not and for all requests.
> >
> > > What value does PF_MEMALLOC add? Is that in order to prevent recursion
> > > into other areas of the swap code (say, if you mix swap-over-nfs with
> > > ordinary swap-to-disk)?
> > >
> >
> > PF_MEMALLOC is normally to prevent the page reclaim recursing into
> > itself. Page reclaim can call the page allocator and that cannot re-enter
> > page reclaim.
> >
> > In the case of swap-over-NFS, PF_MEMALLOC is set only if the socket is
> > being used for swapping. In softirq context, the allocation request is
> > allowed to use PFMEMALLOC reserves to avoid deadlock.
> >
> > I do not see an obvious way to collapse the two flags together.
> > PF_FSTRANS should not mean the PFMEMALLOC reserves can be used and
> > PFMEMALLOC is not set for all requests.
>
> Right, but in this case, we're talking about a GFP_KERNEL allocation
> that always happens in an rpciod workqueue process context, so we still
> won't be able to access the PFMEMALLOC reserves if I understand you
> correctly?
>
Ah, I understand you now. The PFMEMALLOC flag only uses the reserves if
running from softirq context. rpciod is never running in that context and
PF_MEMALLOC in that path is counter-productive. Thanks for catching that.
The actual way to resolve this conflict is to alter the "nfs: enable swap on
NFS" patch in Andrew's tree. Andrew, can you apply this patch and collapse
it with "nfs: enable swap on NFS" please?
---8<---
buildfix: nfs: enable swap on NFS
Stephen Rothwell reported a merge conflict between a MM patch "nfs:
enable swap on NFS" and an NFS patch "nfs: skip commit in
releasepage if we're freeing memory for fs-related reasons".
Trond pointed out that at the points of the conflict the running context
is rpciod and not a softirq context. This patch stops PF_MEMALLOC being
set but rpc_malloc still uses __GFP_MEMALLOC where necessary to allocate
from the reserves. When merged with the "nfs: enable swap on NFS", the
conflict with the NFS tree should disappear.
Signed-off-by: Mel Gorman <mgorman@...e.de>
---
net/sunrpc/xprtsock.c | 11 -----------
1 file changed, 11 deletions(-)
diff --git a/net/sunrpc/xprtsock.c b/net/sunrpc/xprtsock.c
index 83bb0eb..bd59d01 100644
--- a/net/sunrpc/xprtsock.c
+++ b/net/sunrpc/xprtsock.c
@@ -2003,15 +2003,11 @@ static void xs_udp_setup_socket(struct work_struct *work)
container_of(work, struct sock_xprt, connect_worker.work);
struct rpc_xprt *xprt = &transport->xprt;
struct socket *sock = transport->sock;
- unsigned long pflags = current->flags;
int status = -EIO;
if (xprt->shutdown)
goto out;
- if (xprt->swapper)
- current->flags |= PF_MEMALLOC;
-
/* Start by resetting any existing state */
xs_reset_transport(transport);
sock = xs_create_sock(xprt, transport,
@@ -2030,7 +2026,6 @@ static void xs_udp_setup_socket(struct work_struct *work)
out:
xprt_clear_connecting(xprt);
xprt_wake_pending_tasks(xprt, status);
- tsk_restore_flags(current, pflags, PF_MEMALLOC);
}
/*
@@ -2153,15 +2148,11 @@ static void xs_tcp_setup_socket(struct work_struct *work)
container_of(work, struct sock_xprt, connect_worker.work);
struct socket *sock = transport->sock;
struct rpc_xprt *xprt = &transport->xprt;
- unsigned long pflags = current->flags;
int status = -EIO;
if (xprt->shutdown)
goto out;
- if (xprt->swapper)
- current->flags |= PF_MEMALLOC;
-
if (!sock) {
clear_bit(XPRT_CONNECTION_ABORT, &xprt->state);
sock = xs_create_sock(xprt, transport,
@@ -2211,7 +2202,6 @@ static void xs_tcp_setup_socket(struct work_struct *work)
case -EINPROGRESS:
case -EALREADY:
xprt_clear_connecting(xprt);
- tsk_restore_flags(current, pflags, PF_MEMALLOC);
return;
case -EINVAL:
/* Happens, for instance, if the user specified a link
@@ -2224,7 +2214,6 @@ out_eagain:
out:
xprt_clear_connecting(xprt);
xprt_wake_pending_tasks(xprt, status);
- tsk_restore_flags(current, pflags, PF_MEMALLOC);
}
/**
--
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