Date: Mon, 1 Feb 2010 09:46:57 -0500 From: John Baldwin <jhb@freebsd.org> To: Marius Strobl <marius@alchemy.franken.de> Cc: rmacklem@freebsd.org, dfr@freebsd.org, freebsd-stable@freebsd.org, Peter Jeremy <peterjeremy@acm.org> Subject: Re: uma_zalloc_arg complaining about non-sleepable locks Message-ID: <201002010946.57253.jhb@freebsd.org> In-Reply-To: <20100131162854.GC77522@alchemy.franken.de> References: <20100126073336.GA1955@server.vk2pj.dyndns.org> <20100131010618.GA1864@server.vk2pj.dyndns.org> <20100131162854.GC77522@alchemy.franken.de>
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On Sunday 31 January 2010 11:28:54 am Marius Strobl wrote: > On Sun, Jan 31, 2010 at 12:06:18PM +1100, Peter Jeremy wrote: > > Sorry for the delay, I was trying to avoid rebooting my server. > > I've setup a similar environment in VirtualBox to test it. > > > > On 2010-Jan-27 12:52:29 +0100, Marius Strobl <marius@alchemy.franken.de> wrote: > > >Ah, I forgot that using nfsm_aligned() causes nfs_realign() to > > >be a NOP on architectures without strict alignment requirements > > >for performance reasons. That's generally fine but unfortunately > > >that way you don't actually exercise the code which caused the > > >problem before (unfortunately I still don't manage to hit the > > >unaligned case myself). > > > > >Could you please test with #ifdef __NO_STRICT_ALIGNMENT replaced > > >with #if 0 in sys/nfs/nfs_common.h? The vfs.nfs.realign_count > > >counter should also increase then. > > > > I'm not sure what triggers the unaligned case either - I tried > > roughly "tar -cf - -C /mnt/usr src | tar -xf - -C /mnt/tmp" and > > that caused some unaligned accesses (but also completely wedged > > the VBox host). I also tried copying a pile of files off my > > NFS client (FreeBSD-8.x/i386) and that also triggered some > > unaligned accesses without any errors being reported. > > > > Currently, I have: > > vfs.nfs.realign_count: 12 > > vfs.nfs.realign_test: 188817 > > > > I'd say that your patch works. > > John, are you okay with that patch? > http://people.freebsd.org/~marius/fha_extract_info_realign2.diff > > It's intention is to: > - Move nfs_realign() from the NFS client to the shared NFS code and > remove the NFS server version in order to reduce code duplication. > The shared version now uses a second parameter how, which is passed > on to m_get(9) and m_getcl(9) as the server used M_WAIT while the > client requires M_DONTWAIT, and replaces the the previously unused > parameter hsiz. > - Change nfs_realign() to use nfsm_aligned() so as with other NFS code > the alignment check isn't actually performed on platforms without > strict alignment requirements for performance reasons because as the > comment suggests only occasionally occurs with TCP. > - Change fha_extract_info() to use nfs_realign() with M_NOWAIT rather > than M_DONTWAIT because it's called with the RPC sp_lock held. > > The only downside of the shared nfs_realign() are the combined > SYSCTL counters but the fact we incremented them non-atomically > so far I think already indicates that their intention only is a > rough indication rather than exact values for client and server. This all sounds good to me, but isn't M_NOWAIT == M_DONTWAIT? Hmm, reading the code more closely, it looks like fha_extract_info() was using M_WAIT rather than M_DONTWAIT previously. Also, I think you should be careful to use M_DONTWAIT instead of M_NOWAIT for mbufs, so I would fix that in fha_extract_info(). -- John Baldwin
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