linux-kernel - Re: [PATCH 08/20] mm: Optimize fullmm TLB flushing

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Date:	Thu, 28 Jun 2012 01:13:27 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	linux-mm@...ck.org, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, akpm@...ux-foundation.org,
	Rik van Riel <riel@...hat.com>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	Mel Gorman <mel@....ul.ie>, Nick Piggin <npiggin@...nel.dk>,
	Alex Shi <alex.shi@...el.com>,
	"Nikunj A. Dadhania" <nikunj@...ux.vnet.ibm.com>,
	Konrad Rzeszutek Wilk <konrad@...nok.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	David Miller <davem@...emloft.net>,
	Russell King <rmk@....linux.org.uk>,
	Catalin Marinas <catalin.marinas@....com>,
	Chris Metcalf <cmetcalf@...era.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Tony Luck <tony.luck@...el.com>,
	Paul Mundt <lethal@...ux-sh.org>,
	Jeff Dike <jdike@...toit.com>,
	Richard Weinberger <richard@....at>,
	Ralf Baechle <ralf@...ux-mips.org>,
	Kyle McMartin <kyle@...artin.ca>,
	James Bottomley <jejb@...isc-linux.org>,
	Chris Zankel <chris@...kel.net>
Subject: Re: [PATCH 08/20] mm: Optimize fullmm TLB flushing

On Thu, 2012-06-28 at 01:02 +0200, Peter Zijlstra wrote:
> On Wed, 2012-06-27 at 15:26 -0700, Linus Torvalds wrote:
> > On Wed, Jun 27, 2012 at 2:15 PM, Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
> > > This originated from s390 which does something similar and would allow
> > > s390 to use the generic TLB flushing code.
> > >
> > > The idea is to flush the mm wide cache and tlb a priory and not bother
> > > with multiple flushes if the batching isn't large enough.
> > >
> > > This can be safely done since there cannot be any concurrency on this
> > > mm, its either after the process died (exit) or in the middle of
> > > execve where the thread switched to the new mm.
> > 
> > I think we actually *used* to do the final TLB flush from within the
> > context of the process that died. That doesn't seem to ever be the
> > case any more, but it does worry me a bit. Maybe a
> > 
> >    VM_BUG_ON(current->active_mm == mm);
> > 
> > or something for the fullmm case?
> 
> OK, added it and am rebooting the test box..

That triggered.. is this a problem though, at this point userspace is
very dead so it shouldn't matter, right?

Will have to properly think about it tomorrow, its been 1am, brain is
mostly sleeping already.

------------[ cut here ]------------
kernel BUG at /home/root/src/linux-2.6/mm/memory.c:221!
invalid opcode: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC
Modules linked in:
CPU 13 
Pid: 132, comm: modprobe Not tainted 3.5.0-rc4-01507-g912ca15-dirty #180 Supermicro X8DTN/X8DTN
RIP: 0010:[<ffffffff811511bf>]  [<ffffffff811511bf>] tlb_gather_mmu+0x9f/0xb0
RSP: 0018:ffff880235b2bd78  EFLAGS: 00010246
RAX: ffff880235b18000 RBX: ffff880235b2bdc0 RCX: ffff880235b18000
RDX: 0000000000000000 RSI: 0000000000000100 RDI: 0000000000000000
RBP: ffff880235b2bd98 R08: 0000000000000018 R09: 0000000000000004
R10: ffffffff81eedfc0 R11: 0000000000000084 R12: ffff8804356b8000
R13: 0000000000000001 R14: ffff880235b185f0 R15: ffff880235b18000
FS:  0000000000000000(0000) GS:ffff880237ce0000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000038ce8ae150 CR3: 0000000436ad6000 CR4: 00000000000007e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Process modprobe (pid: 132, threadinfo ffff880235b2a000, task ffff880235b18000)
Stack:
 ffff880235b2bd98 0000000000000000 ffff8804356b8000 ffff8804356b8060
 ffff880235b2be38 ffffffff8115ad38 ffff880235b2be38 ffff880235b4e000
 ffff880235b4e630 ffff8804356b8000 0000000100000000 ffff880235b2bdd8
Call Trace:
 [<ffffffff8115ad38>] exit_mmap+0x98/0x150
 [<ffffffff810bf98e>] ? exit_numa+0xae/0xe0
 [<ffffffff81078b74>] mmput+0x84/0x120
 [<ffffffff81080ce8>] exit_mm+0x108/0x130
 [<ffffffff81081388>] do_exit+0x678/0x950
 [<ffffffff811a3ad6>] ? alloc_fd+0xd6/0x120
 [<ffffffff811791c0>] ? kmem_cache_free+0x20/0x130
 [<ffffffff810819af>] do_group_exit+0x3f/0xa0
 [<ffffffff81081a27>] sys_exit_group+0x17/0x20
 [<ffffffff81980ed2>] system_call_fastpath+0x16/0x1b
Code: 10 74 1a 65 48 8b 04 25 80 ba 00 00 4c 3b a0 90 02 00 00 74 16 4c 89 e7 e8 5f 39 f2 ff 48 8b 5d e8 4c 8b 65 f0 4c 8b 6d f8 c9 c3 <0f> 0b 66 66 66 66 66 66 2e 0f 1f 84 00 00 00 00 00 55 48 89 e5 
RIP  [<ffffffff811511bf>] tlb_gather_mmu+0x9f/0xb0
 RSP <ffff880235b2bd78>
---[ end trace f99f121b09c974f8 ]---

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