[PATCH v5 0/6] Use pageblock_order for cma and alloc_contig_range alignment.

Zi Yan
2022-02-11T16:51:07Z

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-2022-02-08-15-31.

Changelog
===
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 range
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 >= pageblock_order, as the case (not
mergeable pageblocks are isolated, CMA, and HIGHATOMIC) becomes more common.
3. Moving has_unmovable_pages() is now a separate patch.
4. Removed MAX_ORDER-1 alignment requirement in the comment in virtio_mem code.

Description
===

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 pageblocks
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 pageblock
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 page
have different migratetypes);
3. only checks unmovable pages within the range instead of MAX_ORDER - 1 aligned
range during isolation to avoid alloc_contig_range() failure when pageblocks
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.com/
[2] https://lore.kernel.org/linux-mm/d19fb078-cb9b-f60f-e310-fdeea1b947d2@redhat.com/

Zi Yan (6):
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.
arch: powerpc: adjust fadump alignment to be pageblock aligned.

arch/powerpc/include/asm/fadump-internal.h | 4 +-
drivers/virtio/virtio_mem.c | 7 +-
include/linux/mmzone.h | 5 +-
include/linux/page-isolation.h | 16 +-
kernel/dma/contiguous.c | 2 +-
mm/cma.c | 6 +-
mm/internal.h | 3 +
mm/memory_hotplug.c | 3 +-
mm/page_alloc.c | 371 ++++++++++-----------
mm/page_isolation.c | 172 +++++++++-
10 files changed, 367 insertions(+), 222 deletions(-)

--
2.34.1