linux-kernel - [RFC PATCH 0/3] PCI/P2PMEM: introduce pci_p2pdma_align

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Date:   Wed, 2 Jun 2021 14:10:52 +0300
From:   Max Gurtovoy <mgurtovoy@...dia.com>
To:     <linux-nvme@...ts.infradead.org>, <dan.j.williams@...el.com>,
        <logang@...tatee.com>, <linux-mm@...ck.org>, <hch@....de>
CC:     <sagi@...mberg.me>, <david@...hat.com>, <oren@...dia.com>,
        <linux-kernel@...r.kernel.org>, <akpm@...ux-foundation.org>,
        Max Gurtovoy <mgurtovoy@...dia.com>
Subject: [RFC PATCH 0/3] PCI/P2PMEM: introduce pci_p2pdma_align_size API

Hi all,
In hotplugged memory (from check_pfn_span function):
"
Disallow all operations smaller than a sub-section and only
allow operations smaller than a section for
SPARSEMEM_VMEMMAP. Note that check_hotplug_memory_range()
enforces a larger memory_block_size_bytes() granularity for
memory that will be marked online, so this check should only
fire for direct arch_{add,remove}_memory() users outside of
add_memory_resource()
"

This restriction will disqualify, for example, large NVMe CMBs that might have
non power of 2 number of pages (e.g. 32767 pages of 4KB). For these
devices, the CMB size will be rounded down from 0x7fff000 to 0x7e00000
but it's better than having un-mapped CMB.

If we all agree on the approach, this RFC can assist as-is to these NVMe
devices and other P2PMEM devices in the future and can considered for
the next merge window.

Max Gurtovoy (3):
  mm,memory_hotplug: export mhp min alignment
  PCI/P2PMEM: introduce pci_p2pdma_align_size API
  nvme-pci: align CMB size according to P2PMEM alignment

 drivers/nvme/host/pci.c        |  7 +++++++
 drivers/pci/p2pdma.c           | 23 +++++++++++++++++++++++
 include/linux/memory_hotplug.h |  5 +++++
 include/linux/pci-p2pdma.h     |  5 +++++
 mm/memory_hotplug.c            | 33 +++++++++++++++++++--------------
 5 files changed, 59 insertions(+), 14 deletions(-)

-- 
2.18.1