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[62.201.165.239]) by smtp.gmail.com with ESMTPSA id a1-v6sm2082587wrt.9.2018.09.27.05.32.54 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 27 Sep 2018 05:32:54 -0700 (PDT) Received: by techadventures.net (Postfix, from userid 1000) id 2B78312561B; Thu, 27 Sep 2018 14:32:54 +0200 (CEST) Date: Thu, 27 Sep 2018 14:32:54 +0200 From: Oscar Salvador To: Alexander Duyck Cc: Michal Hocko , linux-mm@kvack.org, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-nvdimm@lists.01.org, pavel.tatashin@microsoft.com, dave.jiang@intel.com, dave.hansen@intel.com, jglisse@redhat.com, rppt@linux.vnet.ibm.com, dan.j.williams@intel.com, logang@deltatee.com, mingo@kernel.org, kirill.shutemov@linux.intel.com Subject: Re: [PATCH v5 4/4] mm: Defer ZONE_DEVICE page initialization to the point where we init pgmap Message-ID: <20180927123254.GB20378@techadventures.net> References: <20180925200551.3576.18755.stgit@localhost.localdomain> <20180925202053.3576.66039.stgit@localhost.localdomain> <20180926075540.GD6278@dhcp22.suse.cz> <6f87a5d7-05e2-00f4-8568-bb3521869cea@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <6f87a5d7-05e2-00f4-8568-bb3521869cea@linux.intel.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Sep 26, 2018 at 11:25:37AM -0700, Alexander Duyck wrote: > With that said I am open to suggestions if you still feel like I need to > follow this up with some additional work. I just want to avoid introducing > any regressions in regards to functionality or performance. Hi Alexander, the problem I see is that devm/hmm is using some of the memory-hotplug features, but their paths are becoming more and more diverged with changes like this, and that is sometimes a problem when we need to change something in the generic memory-hotplug code. E.g: I am trying to fix two issues in the memory-hotplug where we can access steal pages if we hot-remove memory before online it. That was not so difficult to fix, but I really struggled with the exceptions that HMM/devm represent in this regard, for instance, regarding the resources. The RFCv2 can be found here [1] https://patchwork.kernel.org/patch/10569083/ And the initial discussion with Jerome Glisse can be found here [2]. So it would be great to stick to the memory-hotplug path as much as possible, otherwise when a problem arises, we need to think how we can workaround HMM/devm. [1] https://patchwork.kernel.org/patch/10569083/ [2] https://patchwork.kernel.org/patch/10558725/ -- Oscar Salvador SUSE L3