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From:   Zi Yan <zi.yan@sent.com>
To:     David Hildenbrand <david@redhat.com>, linux-mm@kvack.org
Cc:     linux-kernel@vger.kernel.org,
        Michael Ellerman <mpe@ellerman.id.au>,
        Christoph Hellwig <hch@lst.de>,
        Marek Szyprowski <m.szyprowski@samsung.com>,
        Robin Murphy <robin.murphy@arm.com>,
        linuxppc-dev@lists.ozlabs.org,
        virtualization@lists.linux-foundation.org,
        iommu@lists.linux-foundation.org, Vlastimil Babka <vbabka@suse.cz>,
        Mel Gorman <mgorman@techsingularity.net>,
        Eric Ren <renzhengeek@gmail.com>,
        Mike Rapoport <rppt@kernel.org>,
        Oscar Salvador <osalvador@suse.de>,
        Christophe Leroy <christophe.leroy@csgroup.eu>,
        Zi Yan <ziy@nvidia.com>
Subject: [PATCH v6 0/5] Use pageblock_order for cma and alloc_contig_range alignment.
Date:   Tue, 22 Feb 2022 23:30:32 -0500
Message-Id: <20220223043037.715205-1-zi.yan@sent.com>
Reply-To: Zi Yan <ziy@nvidia.com>
MIME-Version: 1.0
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From: Zi Yan <ziy@nvidia.com>

Hi all,

This patchset tries to remove the MAX_ORDER-1 alignment requirement for CMA
and alloc_contig_range(). It prepares for my upcoming changes to make
MAX_ORDER adjustable at boot time[1]. It is on top of mmotm-2022-02-14-17-4=
6.

Changelog
=3D=3D=3D
V6
---
1. Resolved compilation error/warning reported by kernel test robot.
2. Tried to solve the coding concerns from Christophe Leroy.
3. Shortened lengthy lines (pointed out by Christoph Hellwig).

V5
---
1. Moved isolation address alignment handling in start_isolate_page_range().
2. Rewrote and simplified how alloc_contig_range() works at pageblock
   granularity (Patch 3). Only two pageblock migratetypes need to be saved =
and
   restored. start_isolate_page_range() might need to migrate pages in this
   version, but it prevents the caller from worrying about
   max(MAX_ORDER_NR_PAEGS, pageblock_nr_pages) alignment after the page ran=
ge
   is isolated.

V4
---
1. Dropped two irrelevant patches on non-lru compound page handling, as
   it is not supported upstream.
2. Renamed migratetype_has_fallback() to migratetype_is_mergeable().
3. Always check whether two pageblocks can be merged in
   __free_one_page() when order is >=3D pageblock_order, as the case (not
   mergeable pageblocks are isolated, CMA, and HIGHATOMIC) becomes more com=
mon.
3. Moving has_unmovable_pages() is now a separate patch.
4. Removed MAX_ORDER-1 alignment requirement in the comment in virtio_mem c=
ode.

Description
=3D=3D=3D

The MAX_ORDER - 1 alignment requirement comes from that alloc_contig_range()
isolates pageblocks to remove free memory from buddy allocator but isolating
only a subset of pageblocks within a page spanning across multiple pagebloc=
ks
causes free page accounting issues. Isolated page might not be put into the
right free list, since the code assumes the migratetype of the first pagebl=
ock
as the whole free page migratetype. This is based on the discussion at [2].

To remove the requirement, this patchset:
1. isolates pages at pageblock granularity instead of
   max(MAX_ORDER_NR_PAEGS, pageblock_nr_pages);
2. splits free pages across the specified range or migrates in-use pages
   across the specified range then splits the freed page to avoid free page
   accounting issues (it happens when multiple pageblocks within a single p=
age
   have different migratetypes);
3. only checks unmovable pages within the range instead of MAX_ORDER - 1 al=
igned
   range during isolation to avoid alloc_contig_range() failure when pagebl=
ocks
   within a MAX_ORDER - 1 aligned range are allocated separately.
4. returns pages not in the range as it did before.

One optimization might come later:
1. make MIGRATE_ISOLATE a separate bit to be able to restore the original
   migratetypes when isolation fails in the middle of the range.

Feel free to give comments and suggestions. Thanks.

[1] https://lore.kernel.org/linux-mm/20210805190253.2795604-1-zi.yan@sent.c=
om/
[2] https://lore.kernel.org/linux-mm/d19fb078-cb9b-f60f-e310-fdeea1b947d2@r=
edhat.com/

Zi Yan (5):
  mm: page_isolation: move has_unmovable_pages() to mm/page_isolation.c
  mm: page_isolation: check specified range for unmovable pages
  mm: make alloc_contig_range work at pageblock granularity
  mm: cma: use pageblock_order as the single alignment
  drivers: virtio_mem: use pageblock size as the minimum virtio_mem
    size.

 drivers/virtio/virtio_mem.c    |   6 +-
 include/linux/cma.h            |   4 +-
 include/linux/mmzone.h         |   5 +-
 include/linux/page-isolation.h |  14 +-
 mm/internal.h                  |   6 +
 mm/memory_hotplug.c            |   3 +-
 mm/page_alloc.c                | 246 +++++++--------------------
 mm/page_isolation.c            | 296 +++++++++++++++++++++++++++++++--
 8 files changed, 367 insertions(+), 213 deletions(-)

--=20
2.34.1