Message-ID: <20250523191258.339826-1-ziy@nvidia.com>
Date: Fri, 23 May 2025 15:12:52 -0400
From: Zi Yan <ziy@...dia.com>
To: David Hildenbrand <david@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	linux-mm@...ck.org
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	Oscar Salvador <osalvador@...e.de>,
	Vlastimil Babka <vbabka@...e.cz>,
	Baolin Wang <baolin.wang@...ux.alibaba.com>,
	"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
	Mel Gorman <mgorman@...hsingularity.net>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Michal Hocko <mhocko@...e.com>,
	Brendan Jackman <jackmanb@...gle.com>,
	Richard Chang <richardycc@...gle.com>,
	linux-kernel@...r.kernel.org,
	Zi Yan <ziy@...dia.com>
Subject: [PATCH v5 0/6] Make MIGRATE_ISOLATE a standalone bit

Hi David,

I tried to get rid of pfnblock mask by replacing
{get,set}_pfnblock_flags_mask() with {get,set}_pfnblock_migratetype(),
but get_pfnblock_migratetype() will need to do both test_bit() for
MIGRATE_ISOLATE and try_cmpxchg() for other migratetype, which doubles
its cost. So I made {get,set}_pfnblock_flags_mask() internal and use
them in {get,set}_pfnblock_migratetype(). Let me know your thoughts.

Hi all,

This patchset moves MIGRATE_ISOLATE to a standalone bit to avoid
being overwritten during pageblock isolation process. Currently,
MIGRATE_ISOLATE is part of enum migratetype (in include/linux/mmzone.h),
thus, setting a pageblock to MIGRATE_ISOLATE overwrites its original
migratetype. This causes pageblock migratetype loss during
alloc_contig_range() and memory offline, especially when the process
fails due to a failed pageblock isolation and the code tries to undo the
finished pageblock isolations.

It is on top of mm-everything-2025-05-22-02-14.

In terms of performance for changing pageblock types, no performance
change is observed:

1. I used perf to collect stats of offlining and onlining all memory of a
40GB VM 10 times and see that get_pfnblock_flags_mask() and
set_pfnblock_flags_mask() take about 0.12% and 0.02% of the whole process
respectively with and without this patchset across 3 runs.

2. I used perf to collect stats of dd from /dev/random to a 40GB tmpfs file
and find get_pfnblock_flags_mask() takes about 0.05% of the process with and
without this patchset across 3 runs.


Changelog
===
>From v4[3]:
1. cleaned up existing pageblock flag functions:
   a. added {get,set}_{pfnblock,pageblock}_migratetype() to change
      pageblock migratetype
   b. added {get,set,clear}_pfnblock_bit() to change pageblock
      standalone bit, i.e., PB_migrate_skip and PB_migrate_isolate (added
      in this series).
   c. removed {get,set}_pfnblock_flags_mask().
2. added __NR_PAGEBLOCK_BITS to present the number of pageblock flag bits and
   used roundup_pow_of_two(__NR_PAGEBLOCK_BITS) as NR_PAGEBLOCK_BITS.
3. moved {get,set,clear}_pageblock_isolate() to linux/page-isolation.h.
4. added init_pageblock_migratetype() to initialize a pageblock with a
   migratetype and isolated. It is used by memmap_init_range(), which is
   called by move_pfn_range_to_zone() in online_pages() from
   mm/memory_hotplug.c. Other set_pageblock_migratetype() users are
   changed too except the ones in mm/page_alloc.c.
5. toggle_pageblock_isolate() is reimplemented using __change_bit().
6. set_pageblock_migratetype() gives a warning if a pageblock is changed
   from MIGRATE_ISOLATE to other migratetype.
7. added pb_isolate_mode: MEMORY_OFFLINE, CMA_ALLOCATION, ISOLATE_MODE_OTHERS
   to replace isolate flags.
8. REPORT_FAILURE is removed, since it is only used by MEMORY_OFFLINE.

>From v3[2]:
1. kept the original is_migrate_isolate_page()
2. moved {get,set,clear}_pageblock_isolate() to mm/page_isolation.c
3. used a single version for get_pageblock_migratetype() and
   get_pfnblock_migratetype().
4. replace get_pageblock_isolate() with
   get_pageblock_migratetype() == MIGRATE_ISOLATE, a
   get_pageblock_isolate() becomes private in mm/page_isolation.c
5. made set_pageblock_migratetype() not accept MIGRATE_ISOLATE, so that
   people need to use the dedicate {get,set,clear}_pageblock_isolate() APIs.
6. changed online_page() from mm/memory_hotplug.c to first set pageblock
   migratetype to MIGRATE_MOVABLE, then isolate pageblocks.
7. added __maybe_unused to get_pageblock_isolate(), since it is only
   used in VM_BUG_ON(), which could be not present when MM debug is off.
   It is reported by kernel test robot.
7. fixed test_pages_isolated() type issues reported by kernel test
   robot.

>From v2[1]:
1. Moved MIGRATETYPE_NO_ISO_MASK to Patch 2, where it is used.
2. Removed spurious changes in Patch 1.
3. Refactored code so that migratetype mask is passed properly for all
callers to {get,set}_pfnblock_flags_mask().
4. Added toggle_pageblock_isolate() for setting and clearing
MIGRATE_ISOLATE.
5. Changed get_pageblock_migratetype() when CONFIG_MEMORY_ISOLATION to
handle MIGRATE_ISOLATE case. It acts like a parsing layer for
get_pfnblock_flags_mask().


Design
===

Pageblock flags are read in words to achieve good performance and existing
pageblock flags take 4 bits per pageblock. To avoid a substantial change
to the pageblock flag code, 8 pageblock flag bits are used.

It might look like the pageblock flags have doubled the overhead, but in
reality, the overhead is only 1 byte per 2MB/4MB (based on pageblock config),
or 0.0000476 %.

Any comment and/or suggestion is welcome. Thanks.

[1] https://lore.kernel.org/linux-mm/20250214154215.717537-1-ziy@nvidia.com/
[2] https://lore.kernel.org/linux-mm/20250507211059.2211628-2-ziy@nvidia.com/
[3] https://lore.kernel.org/linux-mm/20250509200111.3372279-1-ziy@nvidia.com/

Zi Yan (6):
  mm/page_alloc: pageblock flags functions clean up.
  mm/page_isolation: make page isolation a standalone bit.
  mm/page_alloc: add support for initializing pageblock as isolated.
  mm/page_isolation: remove migratetype from
    move_freepages_block_isolate()
  mm/page_isolation: remove migratetype from undo_isolate_page_range()
  mm/page_isolation: remove migratetype parameter from more functions.

 drivers/virtio/virtio_mem.c     |   3 +-
 include/linux/gfp.h             |   6 +-
 include/linux/memory_hotplug.h  |   3 +-
 include/linux/mmzone.h          |  18 +-
 include/linux/page-isolation.h  |  46 ++++-
 include/linux/pageblock-flags.h |  45 +++--
 include/trace/events/kmem.h     |  14 +-
 mm/cma.c                        |   2 +-
 mm/hugetlb.c                    |   4 +-
 mm/internal.h                   |   3 +-
 mm/memory_hotplug.c             |  22 +-
 mm/memremap.c                   |   2 +-
 mm/mm_init.c                    |  24 ++-
 mm/page_alloc.c                 | 342 +++++++++++++++++++++++++-------
 mm/page_isolation.c             |  97 ++++-----
 15 files changed, 441 insertions(+), 190 deletions(-)

-- 
2.47.2

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