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Y. Srinivasan" , Michal Hocko , =?UTF-8?q?Roger=20Pau=20Monn=C3=A9?= , Stefano Stabellini , Stephen Hemminger , Thomas Gleixner , Wei Liu , Wei Yang Subject: [PATCH RFCv1 0/5] mm/memory_hotplug: selective merging of memory resources Date: Fri, 31 Jul 2020 11:18:33 +0200 Message-Id: <20200731091838.7490-1-david@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Rspamd-Queue-Id: 5094E18140B74 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam02 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: Some add_memory*() users add memory in small, contiguous memory blocks. Examples include virtio-mem, hyper-v balloon, and the XEN balloon. This can quickly result in a lot of memory resources, whereby the actual resource boundaries are not of interest (e.g., it might be relevant for DIMMs, exposed via /proc/iomem to user space). We really want to merge added resources in this scenario where possible. Resources are effectively stored in a list-based tree. Having a lot of resources not only wastes memory, it also makes traversing that tree more expensive, and makes /proc/iomem explode in size (e.g., requiring kexec-tools to manually merge resources when creating a kdump header. The current kexec-tools resource count limit does not allow more than ~100GB of memory with a memory block size of 128MB on x86-64). Let's allow to selectively merge resources, speciyfing a parent node and a resource idendifier string. The memory unplug path will properly split up merged resources again. Patch #3 contains a /proc/iomem example. Only tested with virtio-mem. Note: This gets the job done and is comparably simple. More complicated approaches would require introducing IORESOURCE_MERGEABLE and extending o= ur add_memory*() interfaces with a flag, specifying that merging after addin= g succeeded is acceptable. I'd like to avoid that complexity and code churn for now. David Hildenbrand (5): kernel/resource: make release_mem_region_adjustable() never fail kernel/resource: merge_child_mem_resources() to merge memory resources after adding succeeded virtio-mem: try to merge "System RAM (virtio_mem)" resources xen/balloon: try to merge "System RAM" resources hv_balloon:: try to merge "System RAM" resources drivers/hv/hv_balloon.c | 3 ++ drivers/virtio/virtio_mem.c | 14 ++++- drivers/xen/balloon.c | 4 ++ include/linux/ioport.h | 7 ++- kernel/resource.c | 105 ++++++++++++++++++++++++++++-------- mm/memory_hotplug.c | 22 +------- 6 files changed, 109 insertions(+), 46 deletions(-) --=20 2.26.2