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Tue, 08 Sep 2020 14:03:38 -0400 X-MC-Unique: eApXzjhRMXu9CMjhByTNBA-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id A69698015F6; Tue, 8 Sep 2020 18:03:35 +0000 (UTC) Received: from [10.36.115.46] (ovpn-115-46.ams2.redhat.com [10.36.115.46]) by smtp.corp.redhat.com (Postfix) with ESMTP id 695DF7A1F9; Tue, 8 Sep 2020 18:03:32 +0000 (UTC) Subject: Re: [PATCH v4 11/23] device-dax: Kill dax_kmem_res To: Joao Martins , Dan Williams Cc: akpm@linux-foundation.org, Vishal Verma , Dave Hansen , Pavel Tatashin , peterz@infradead.org, ard.biesheuvel@linaro.org, linux-mm@kvack.org, linux-nvdimm@lists.01.org, linux-kernel@vger.kernel.org, linux-acpi@vger.kernel.org, dri-devel@lists.freedesktop.org References: <159643094279.4062302.17779410714418721328.stgit@dwillia2-desk3.amr.corp.intel.com> <159643100485.4062302.976628339798536960.stgit@dwillia2-desk3.amr.corp.intel.com> <17686fcc-202e-0982-d0de-54d5349cfb5d@oracle.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 MIME-Version: 1.0 In-Reply-To: <17686fcc-202e-0982-d0de-54d5349cfb5d@oracle.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Rspamd-Queue-Id: B5C6B1A4AF X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam01 Content-Transfer-Encoding: quoted-printable 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: >>> + release_mem_region(range.start, range_len(&range)); >> >> remove_memory() does a release_mem_region_adjustable(). Don't you >> actually want to release the *unaligned* region you requested? >> > Isn't it what we're doing here? > (The release_mem_region_adjustable() is using the same > dax_kmem-aligned range and there's no split/adjust) Oh, I think I was messing up things (there is just too much going on in this patch). Right, request_mem_region() and add_memory_driver_managed() are - and were - called with the exact same range. That would have been clearer if the patch would simply use range.start and range_len(&range) for both calls (similar in the original code). So, also the release calls have to use the same range. Agreed. >=20 > Meaning right now (+ parent marked as !BUSY), and if I am understanding > this correctly: >=20 > request_mem_region(range.start, range_len) > __request_region(iomem_res, range.start, range_len) -> alloc @parent > add_memory_driver_managed(parent.start, resource_size(parent)) > __request_region(parent.start, resource_size(parent)) -> alloc @chil= d >=20 > [...] >=20 > remove_memory(range.start, range_len) > request_mem_region_adjustable(range.start, range_len) > __release_region(range.start, range_len) -> remove @child >=20 > release_mem_region(range.start, range_len) > __release_region(range.start, range_len) -> doesn't remove @parent be= cause !BUSY? >=20 > The add/removal of this relies on !BUSY. But now I am wondering if the = parent remaining > unreleased is deliberate even on CONFIG_MEMORY_HOTREMOVE=3Dy. Interesting, I can only tell that virtio-mem expects that remove_memory() won't remove the parent resource (which is !BUSY). So it relies on the existing functionality. I do wonder how walk_system_ram_range() behaves if both the parent and the child are BUSY. Looking at it, I think it will detect the parent and skip to the next range (without visiting the child) - which is not what we want. We could set the parent to BUSY just before doing the release_mem_region() call, but that feels like a hack. Maybe it's just easier to keep dax_kmem_res around ... --=20 Thanks, David / dhildenb