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[195.135.220.15]) by mx.google.com with ESMTPS id t54si9075252edd.313.2019.07.24.11.56.20 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 24 Jul 2019 11:56:20 -0700 (PDT) Received-SPF: softfail (google.com: domain of transitioning mhocko@kernel.org does not designate 195.135.220.15 as permitted sender) client-ip=195.135.220.15; Authentication-Results: mx.google.com; spf=softfail (google.com: domain of transitioning mhocko@kernel.org does not designate 195.135.220.15 as permitted sender) smtp.mailfrom=mhocko@kernel.org; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=kernel.org X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 377DCAE1B; Wed, 24 Jul 2019 18:56:20 +0000 (UTC) Date: Wed, 24 Jul 2019 20:56:17 +0200 From: Michal Hocko To: Jason Gunthorpe Cc: Christoph Hellwig , Ralph Campbell , linux-mm@kvack.org, linux-kernel@vger.kernel.org, nouveau@lists.freedesktop.org, dri-devel@lists.freedesktop.org, =?iso-8859-1?B?Suly9G1l?= Glisse , Ben Skeggs Subject: Re: [PATCH] mm/hmm: replace hmm_update with mmu_notifier_range Message-ID: <20190724185617.GE6410@dhcp22.suse.cz> References: <20190723210506.25127-1-rcampbell@nvidia.com> <20190724070553.GA2523@lst.de> <20190724152858.GB28493@ziepe.ca> <20190724175858.GC6410@dhcp22.suse.cz> <20190724180837.GF28493@ziepe.ca> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190724180837.GF28493@ziepe.ca> User-Agent: Mutt/1.10.1 (2018-07-13) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed 24-07-19 15:08:37, Jason Gunthorpe wrote: > On Wed, Jul 24, 2019 at 07:58:58PM +0200, Michal Hocko wrote: [...] > > Maybe new users have started relying on a new semantic in the meantime, > > back then, none of the notifier has even started any action in blocking > > mode on a EAGAIN bailout. Most of them simply did trylock early in the > > process and bailed out so there was nothing to do for the range_end > > callback. > > Single notifiers are not the problem. I tried to make this clear in > the commit message, but lets be more explicit. > > We have *two* notifiers registered to the mm, A and B: > > A invalidate_range_start: (has no blocking) > spin_lock() > counter++ > spin_unlock() > > A invalidate_range_end: > spin_lock() > counter-- > spin_unlock() > > And this one: > > B invalidate_range_start: (has blocking) > if (!try_mutex_lock()) > return -EAGAIN; > counter++ > mutex_unlock() > > B invalidate_range_end: > spin_lock() > counter-- > spin_unlock() > > So now the oom path does: > > invalidate_range_start_non_blocking: > for each mn: > a->invalidate_range_start > b->invalidate_range_start > rc = EAGAIN > > Now we SKIP A's invalidate_range_end even though A had no idea this > would happen has state that needs to be unwound. A is broken. > > B survived just fine. > > A and B *alone* work fine, combined they fail. But that requires that they share some state, right? > When the commit was landed you can use KVM as an example of A and RDMA > ODP as an example of B Could you point me where those two share the state please? KVM seems to be using kvm->mmu_notifier_count but I do not know where to look for the RDMA... -- Michal Hocko SUSE Labs