Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756759AbdLOQZr (ORCPT ); Fri, 15 Dec 2017 11:25:47 -0500 Received: from mx2.suse.de ([195.135.220.15]:34695 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932508AbdLOQZm (ORCPT ); Fri, 15 Dec 2017 11:25:42 -0500 Date: Fri, 15 Dec 2017 17:25:34 +0100 From: Michal Hocko To: David Rientjes Cc: Andrew Morton , Andrea Arcangeli , Benjamin Herrenschmidt , Paul Mackerras , Oded Gabbay , Alex Deucher , Christian =?iso-8859-1?Q?K=F6nig?= , David Airlie , Joerg Roedel , Doug Ledford , Jani Nikula , Mike Marciniszyn , Sean Hefty , Dimitri Sivanich , Boris Ostrovsky , =?iso-8859-1?B?Suly9G1l?= Glisse , Paolo Bonzini , Radim =?utf-8?B?S3LEjW3DocWZ?= , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [patch v2 1/2] mm, mmu_notifier: annotate mmu notifiers with blockable invalidate callbacks Message-ID: <20171215162534.GA16951@dhcp22.suse.cz> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.1 (2017-09-22) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3323 Lines: 92 On Thu 14-12-17 13:30:56, David Rientjes wrote: > Commit 4d4bbd8526a8 ("mm, oom_reaper: skip mm structs with mmu notifiers") > prevented the oom reaper from unmapping private anonymous memory with the > oom reaper when the oom victim mm had mmu notifiers registered. > > The rationale is that doing mmu_notifier_invalidate_range_{start,end}() > around the unmap_page_range(), which is needed, can block and the oom > killer will stall forever waiting for the victim to exit, which may not > be possible without reaping. > > That concern is real, but only true for mmu notifiers that have blockable > invalidate_range_{start,end}() callbacks. This patch adds a "flags" field > to mmu notifier ops that can set a bit to indicate that these callbacks do > not block. > > The implementation is steered toward an expensive slowpath, such as after > the oom reaper has grabbed mm->mmap_sem of a still alive oom victim. > > Signed-off-by: David Rientjes Yes, this make sense. I haven't checked all the existing mmu notifiers but those that you have marked seem to be OK. I just think that the semantic of the flag should be describe more. See below Acked-by: Michal Hocko > --- > v2: > - specifically exclude mmu_notifiers without invalidate callbacks > - move flags to mmu_notifier_ops per Paolo > - reverse flag from blockable -> not blockable per Christian > > drivers/infiniband/hw/hfi1/mmu_rb.c | 1 + > drivers/iommu/amd_iommu_v2.c | 1 + > drivers/iommu/intel-svm.c | 1 + > drivers/misc/sgi-gru/grutlbpurge.c | 1 + > include/linux/mmu_notifier.h | 21 +++++++++++++++++++++ > mm/mmu_notifier.c | 31 +++++++++++++++++++++++++++++++ > virt/kvm/kvm_main.c | 1 + > 7 files changed, 57 insertions(+) > [...] > diff --git a/include/linux/mmu_notifier.h b/include/linux/mmu_notifier.h > --- a/include/linux/mmu_notifier.h > +++ b/include/linux/mmu_notifier.h > @@ -10,6 +10,9 @@ > struct mmu_notifier; > struct mmu_notifier_ops; > > +/* mmu_notifier_ops flags */ > +#define MMU_INVALIDATE_DOES_NOT_BLOCK (0x01) > + > #ifdef CONFIG_MMU_NOTIFIER > > /* > @@ -26,6 +29,15 @@ struct mmu_notifier_mm { > }; > > struct mmu_notifier_ops { > + /* > + * Flags to specify behavior of callbacks for this MMU notifier. > + * Used to determine which context an operation may be called. > + * > + * MMU_INVALIDATE_DOES_NOT_BLOCK: invalidate_{start,end} does not > + * block > + */ > + int flags; This should be more specific IMHO. What do you think about the following wording? invalidate_{start,end,range} doesn't block on any locks which depend directly or indirectly (via lock chain or resources e.g. worker context) on a memory allocation. > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c > --- a/virt/kvm/kvm_main.c > +++ b/virt/kvm/kvm_main.c > @@ -476,6 +476,7 @@ static void kvm_mmu_notifier_release(struct mmu_notifier *mn, > } > > static const struct mmu_notifier_ops kvm_mmu_notifier_ops = { > + .flags = MMU_INVALIDATE_DOES_NOT_BLOCK, > .invalidate_range_start = kvm_mmu_notifier_invalidate_range_start, > .invalidate_range_end = kvm_mmu_notifier_invalidate_range_end, > .clear_flush_young = kvm_mmu_notifier_clear_flush_young, -- Michal Hocko SUSE Labs