From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail172.messagelabs.com (mail172.messagelabs.com [216.82.254.3]) by kanga.kvack.org (Postfix) with SMTP id 7E2F76B006A for ; Sun, 10 Oct 2010 10:26:10 -0400 (EDT) Date: Sun, 10 Oct 2010 16:25:51 +0200 From: Gleb Natapov Subject: Re: [PATCH v6 10/12] Handle async PF in non preemptable context Message-ID: <20101010142551.GQ2397@redhat.com> References: <1286207794-16120-1-git-send-email-gleb@redhat.com> <1286207794-16120-11-git-send-email-gleb@redhat.com> <20101005195149.GC1786@amt.cnet> <20101006104132.GS11145@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20101006104132.GS11145@redhat.com> Sender: owner-linux-mm@kvack.org To: Marcelo Tosatti Cc: kvm@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, avi@redhat.com, mingo@elte.hu, a.p.zijlstra@chello.nl, tglx@linutronix.de, hpa@zytor.com, riel@redhat.com, cl@linux-foundation.org List-ID: On Wed, Oct 06, 2010 at 12:41:32PM +0200, Gleb Natapov wrote: > On Tue, Oct 05, 2010 at 04:51:50PM -0300, Marcelo Tosatti wrote: > > On Mon, Oct 04, 2010 at 05:56:32PM +0200, Gleb Natapov wrote: > > > If async page fault is received by idle task or when preemp_count is > > > not zero guest cannot reschedule, so do sti; hlt and wait for page to be > > > ready. vcpu can still process interrupts while it waits for the page to > > > be ready. > > > > > > Acked-by: Rik van Riel > > > Signed-off-by: Gleb Natapov > > > --- > > > arch/x86/kernel/kvm.c | 40 ++++++++++++++++++++++++++++++++++------ > > > 1 files changed, 34 insertions(+), 6 deletions(-) > > > > > > diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c > > > index 36fb3e4..f73946f 100644 > > > --- a/arch/x86/kernel/kvm.c > > > +++ b/arch/x86/kernel/kvm.c > > > @@ -37,6 +37,7 @@ > > > #include > > > #include > > > #include > > > +#include > > > > > > #define MMU_QUEUE_SIZE 1024 > > > > > > @@ -78,6 +79,8 @@ struct kvm_task_sleep_node { > > > wait_queue_head_t wq; > > > u32 token; > > > int cpu; > > > + bool halted; > > > + struct mm_struct *mm; > > > }; > > > > > > static struct kvm_task_sleep_head { > > > @@ -106,6 +109,11 @@ void kvm_async_pf_task_wait(u32 token) > > > struct kvm_task_sleep_head *b = &async_pf_sleepers[key]; > > > struct kvm_task_sleep_node n, *e; > > > DEFINE_WAIT(wait); > > > + int cpu, idle; > > > + > > > + cpu = get_cpu(); > > > + idle = idle_cpu(cpu); > > > + put_cpu(); > > > > > > spin_lock(&b->lock); > > > e = _find_apf_task(b, token); > > > @@ -119,19 +127,33 @@ void kvm_async_pf_task_wait(u32 token) > > > > > > n.token = token; > > > n.cpu = smp_processor_id(); > > > + n.mm = current->active_mm; > > > + n.halted = idle || preempt_count() > 1; > > > + atomic_inc(&n.mm->mm_count); > > > > Can't see why this reference is needed. > I thought that if kernel thread does fault on behalf of some > process mm can go away while kernel thread is sleeping. But it looks > like kernel thread increase reference to mm it runs with by himself, so > may be this is redundant (but not harmful). > Actually it is not redundant. Kernel thread will release reference to active_mm on reschedule. -- Gleb. -- 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