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Message-ID: <20150604130830.GH26425@suse.de> Date: Thu, 4 Jun 2015 14:08:30 +0100 From: Mel Gorman <mgorman@...e.de> To: Jeff Layton <jlayton@...chiereds.net> Cc: trond.myklebust@...marydata.com, linux-nfs@...r.kernel.org, linux-mm@...ck.org, linux-kernel@...r.kernel.org, Jerome Marchand <jmarchan@...hat.com> Subject: Re: [PATCH 3/4] sunrpc: if we're closing down a socket, clear memalloc on it first On Wed, Jun 03, 2015 at 10:32:00AM -0400, Jeff Layton wrote: > On Tue, 2 Jun 2015 13:40:26 +0100 > Mel Gorman <mgorman@...e.de> wrote: > > > On Sat, May 30, 2015 at 08:03:12AM -0400, Jeff Layton wrote: > > > We currently increment the memalloc_socks counter if we have a xprt that > > > is associated with a swapfile. That socket can be replaced however > > > during a reconnect event, and the memalloc_socks counter is never > > > decremented if that occurs. > > > > > > When tearing down a xprt socket, check to see if the xprt is set up for > > > swapping and sk_clear_memalloc before releasing the socket if so. > > > > > > Cc: Mel Gorman <mgorman@...e.de> > > > Signed-off-by: Jeff Layton <jeff.layton@...marydata.com> > > > > Acked-by: Mel Gorman <mgorman@...e.de> > > > > Thanks Mel, > > I should also mention that I see this warning pop when working with > swapfiles on NFS. This trace is with this patchset, but I see a similar > one without it: > > [ 74.232485] ------------[ cut here ]------------ > [ 74.233354] WARNING: CPU: 2 PID: 754 at net/core/sock.c:364 sk_clear_memalloc+0x51/0x80() > [ 74.234790] Modules linked in: cts rpcsec_gss_krb5 nfsv4 dns_resolver nfs fscache xfs libcrc32c snd_hda_codec_generic snd_hda_intel snd_hda_controller snd_hda_codec snd_hda_core snd_hwdep snd_seq snd_seq_device nfsd snd_pcm snd_timer snd e1000 ppdev parport_pc joydev parport pvpanic soundcore floppy serio_raw i2c_piix4 pcspkr nfs_acl lockd virtio_balloon acpi_cpufreq auth_rpcgss grace sunrpc qxl drm_kms_helper ttm drm virtio_console virtio_blk virtio_pci ata_generic virtio_ring pata_acpi virtio > [ 74.243599] CPU: 2 PID: 754 Comm: swapoff Not tainted 4.1.0-rc6+ #5 > [ 74.244635] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011 > [ 74.245546] 0000000000000000 0000000079e69e31 ffff8800d066bde8 ffffffff8179263d > [ 74.246786] 0000000000000000 0000000000000000 ffff8800d066be28 ffffffff8109e6fa > [ 74.248175] 0000000000000000 ffff880118d48000 ffff8800d58f5c08 ffff880036e380a8 > [ 74.249483] Call Trace: > [ 74.249872] [<ffffffff8179263d>] dump_stack+0x45/0x57 > [ 74.250703] [<ffffffff8109e6fa>] warn_slowpath_common+0x8a/0xc0 > [ 74.251655] [<ffffffff8109e82a>] warn_slowpath_null+0x1a/0x20 > [ 74.252585] [<ffffffff81661241>] sk_clear_memalloc+0x51/0x80 > [ 74.253519] [<ffffffffa0116c72>] xs_disable_swap+0x42/0x80 [sunrpc] > [ 74.254537] [<ffffffffa01109de>] rpc_clnt_swap_deactivate+0x7e/0xc0 [sunrpc] > [ 74.255610] [<ffffffffa03e4fd7>] nfs_swap_deactivate+0x27/0x30 [nfs] > [ 74.256582] [<ffffffff811e99d4>] destroy_swap_extents+0x74/0x80 > [ 74.257496] [<ffffffff811ecb52>] SyS_swapoff+0x222/0x5c0 > [ 74.258318] [<ffffffff81023f27>] ? syscall_trace_leave+0xc7/0x140 > [ 74.259253] [<ffffffff81798dae>] system_call_fastpath+0x12/0x71 > [ 74.260158] ---[ end trace 2530722966429f10 ]--- > > ...that comes from this in sk_clear_memalloc: > > /* > * SOCK_MEMALLOC is allowed to ignore rmem limits to ensure forward > * progress of swapping. However, if SOCK_MEMALLOC is cleared while > * it has rmem allocations there is a risk that the user of the > * socket cannot make forward progress due to exceeding the rmem > * limits. By rights, sk_clear_memalloc() should only be called > * on sockets being torn down but warn and reset the accounting if > * that assumption breaks. > */ > if (WARN_ON(sk->sk_forward_alloc)) > sk_mem_reclaim(sk); > > Is it wrong to call sk_clear_memalloc on swapoff? Should we try to keep > it set up as a memalloc socket on the last swapoff and just wait until > the socket is being freed to clear it? If so, then maybe the right > thing to do is to call sk_clear_memalloc in __sk_free or somewhere > similar if it's set up for memalloc? > I think it is perfectly reasonable to remove the warning after your series. When I had it in mind, I was primarily thinking of the shutdown case and a single swap file. With your series applied, the disabling of swap is called at the correct time. So, something like this to tack on to the end of your series? ---8<--- net, swap: Remove a warning and clarify why sk_mem_reclaim is required when deactivating swap Jeff Layton reported the following; [ 74.232485] ------------[ cut here ]------------ [ 74.233354] WARNING: CPU: 2 PID: 754 at net/core/sock.c:364 sk_clear_memalloc+0x51/0x80() [ 74.234790] Modules linked in: cts rpcsec_gss_krb5 nfsv4 dns_resolver nfs fscache xfs libcrc32c snd_hda_codec_generic snd_hda_intel snd_hda_controller snd_hda_codec snd_hda_core snd_hwdep snd_seq snd_seq_device nfsd snd_pcm snd_timer snd e1000 ppdev parport_pc joydev parport pvpanic soundcore floppy serio_raw i2c_piix4 pcspkr nfs_acl lockd virtio_balloon acpi_cpufreq auth_rpcgss grace sunrpc qxl drm_kms_helper ttm drm virtio_console virtio_blk virtio_pci ata_generic virtio_ring pata_acpi virtio [ 74.243599] CPU: 2 PID: 754 Comm: swapoff Not tainted 4.1.0-rc6+ #5 [ 74.244635] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011 [ 74.245546] 0000000000000000 0000000079e69e31 ffff8800d066bde8 ffffffff8179263d [ 74.246786] 0000000000000000 0000000000000000 ffff8800d066be28 ffffffff8109e6fa [ 74.248175] 0000000000000000 ffff880118d48000 ffff8800d58f5c08 ffff880036e380a8 [ 74.249483] Call Trace: [ 74.249872] [<ffffffff8179263d>] dump_stack+0x45/0x57 [ 74.250703] [<ffffffff8109e6fa>] warn_slowpath_common+0x8a/0xc0 [ 74.251655] [<ffffffff8109e82a>] warn_slowpath_null+0x1a/0x20 [ 74.252585] [<ffffffff81661241>] sk_clear_memalloc+0x51/0x80 [ 74.253519] [<ffffffffa0116c72>] xs_disable_swap+0x42/0x80 [sunrpc] [ 74.254537] [<ffffffffa01109de>] rpc_clnt_swap_deactivate+0x7e/0xc0 [sunrpc] [ 74.255610] [<ffffffffa03e4fd7>] nfs_swap_deactivate+0x27/0x30 [nfs] [ 74.256582] [<ffffffff811e99d4>] destroy_swap_extents+0x74/0x80 [ 74.257496] [<ffffffff811ecb52>] SyS_swapoff+0x222/0x5c0 [ 74.258318] [<ffffffff81023f27>] ? syscall_trace_leave+0xc7/0x140 [ 74.259253] [<ffffffff81798dae>] system_call_fastpath+0x12/0x71 [ 74.260158] ---[ end trace 2530722966429f10 ]--- The warning in question was unnecessary but with Jeff's series the rules are also clearer. This patch removes the warning and updates the comment to explain why sk_mem_reclaim() may still be called. Signed-off-by: Mel Gorman <mgorman@...e.de> --- net/core/sock.c | 12 +++++------- 1 file changed, 5 insertions(+), 7 deletions(-) diff --git a/net/core/sock.c b/net/core/sock.c index 71e3e5f1eaa0..1ebf706b5847 100644 --- a/net/core/sock.c +++ b/net/core/sock.c @@ -354,14 +354,12 @@ void sk_clear_memalloc(struct sock *sk) /* * SOCK_MEMALLOC is allowed to ignore rmem limits to ensure forward - * progress of swapping. However, if SOCK_MEMALLOC is cleared while - * it has rmem allocations there is a risk that the user of the - * socket cannot make forward progress due to exceeding the rmem - * limits. By rights, sk_clear_memalloc() should only be called - * on sockets being torn down but warn and reset the accounting if - * that assumption breaks. + * progress of swapping. SOCK_MEMALLOC may be cleared while + * it has rmem allocations due to the last swapfile being deactivated + * but there is a risk that the socket is unusable due to exceeding + * the rmem limits. Reclaim the reserves and obey rmem limits again. */ - if (WARN_ON(sk->sk_forward_alloc)) + if (sk->sk_forward_alloc) sk_mem_reclaim(sk); } EXPORT_SYMBOL_GPL(sk_clear_memalloc); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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