Return-Path: Received: from mail-wi0-f179.google.com ([209.85.212.179]:37323 "EHLO mail-wi0-f179.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933379AbbFJIMg convert rfc822-to-8bit (ORCPT ); Wed, 10 Jun 2015 04:12:36 -0400 Received: by wifx6 with SMTP id x6so38807671wif.0 for ; Wed, 10 Jun 2015 01:12:35 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <1433875204-18060-1-git-send-email-jeff.layton@primarydata.com> References: <1433875204-18060-1-git-send-email-jeff.layton@primarydata.com> From: Leon Romanovsky Date: Wed, 10 Jun 2015 11:12:14 +0300 Message-ID: Subject: Re: [PATCH] net, swap: Remove a warning and clarify why sk_mem_reclaim is required when deactivating swap To: Jeff Layton Cc: trond.myklebust@primarydata.com, davem@davemloft.net, netdev@vger.kernel.org, linux-nfs@vger.kernel.org, "linux-kernel@vger.kernel.org" , Mel Gorman , Linux-MM Content-Type: text/plain; charset=UTF-8 Sender: linux-nfs-owner@vger.kernel.org List-ID: On Tue, Jun 9, 2015 at 9:40 PM, Jeff Layton wrote: > From: Mel Gorman > > 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] [] dump_stack+0x45/0x57 > [ 74.250703] [] warn_slowpath_common+0x8a/0xc0 > [ 74.251655] [] warn_slowpath_null+0x1a/0x20 > [ 74.252585] [] sk_clear_memalloc+0x51/0x80 > [ 74.253519] [] xs_disable_swap+0x42/0x80 [sunrpc] > [ 74.254537] [] rpc_clnt_swap_deactivate+0x7e/0xc0 [sunrpc] > [ 74.255610] [] nfs_swap_deactivate+0x27/0x30 [nfs] > [ 74.256582] [] destroy_swap_extents+0x74/0x80 > [ 74.257496] [] SyS_swapoff+0x222/0x5c0 > [ 74.258318] [] ? syscall_trace_leave+0xc7/0x140 > [ 74.259253] [] 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 > Acked-by: Jeff Layton > --- > 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 292f42228bfb..2bb4c56370e5 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) You don't really need this IF. if sk->sk_forward_alloc is equal to zero, it will be less than SK_MEM_QUANTUM. http://lxr.free-electrons.com/source/include/net/sock.h#L1405 1405 static inline void sk_mem_reclaim(struct sock *sk) 1406 { 1407 if (!sk_has_account(sk)) 1408 return; 1409 if (sk->sk_forward_alloc >= SK_MEM_QUANTUM) 1410 __sk_mem_reclaim(sk); 1411 } > sk_mem_reclaim(sk); > } > EXPORT_SYMBOL_GPL(sk_clear_memalloc); > -- > 2.4.2 > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@kvack.org. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: email@kvack.org -- Leon Romanovsky | Independent Linux Consultant www.leon.nu | leon@leon.nu