On my arm64 server with 128 cores, 2 numa nodes.

I used memhog as benchmark :

    numactl -m -C 5 memhog -r100000 1G

The test result as below:

 With this patch:

    #time migratepages 8490 0 1

    real 0m1.161s

    user 0m0.000s

    sys 0m1.161s

without this patch:

    #time migratepages 8460 0 1

    real 0m2.068s

    user 0m0.001s

    sys 0m2.068s

So you can see the  migration performance improvement about +78%

This is the perf  record info.

w/o
+   51.07%     0.09%  migratepages  [kernel.kallsyms]  [k] migrate_folio_extra                                        
+   42.43%     0.04%  migratepages  [kernel.kallsyms]  [k] folio_copy                                                  
+   42.34%    42.34%  migratepages  [kernel.kallsyms]  [k] __pi_copy_page                                             
+   33.99%     0.09%  migratepages  [kernel.kallsyms]  [k] rmap_walk_anon                                             
+   32.35%     0.04%  migratepages  [kernel.kallsyms]  [k] try_to_migrate                                             
+   27.78%    27.78%  migratepages  [kernel.kallsyms]  [k] ptep_clear_flush                                          
+    8.19%     6.64%  migratepages  [kernel.kallsyms]  [k] folio_migrate_flagsmigrati_tlb_flush

w/ this patch
+   18.57%     0.13%  migratepages     [kernel.kallsyms]   [k] migrate_pages                                 
+   18.23%     0.07%  migratepages     [kernel.kallsyms]   [k] migrate_pages_batch                          
+   16.29%     0.13%  migratepages     [kernel.kallsyms]   [k] migrate_folio_move                             
+   12.73%     0.10%  migratepages     [kernel.kallsyms]   [k] move_to_new_folio                           
+   12.52%     0.06%  migratepages     [kernel.kallsyms]   [k] migrate_folio_extra
 

Therefore, this patch helps improve performance in page migration

From: "Huang, Ying" <ying.huang@intel.com>

Now, migrate_pages() migrate folios one by one, like the fake code as
follows,

  for each folio
    unmap
    flush TLB
    copy
    restore map

If multiple folios are passed to migrate_pages(), there are
opportunities to batch the TLB flushing and copying.  That is, we can
change the code to something as follows,

  for each folio
    unmap
  for each folio
    flush TLB
  for each folio
    copy
  for each folio
    restore map

The total number of TLB flushing IPI can be reduced considerably.  And
we may use some hardware accelerator such as DSA to accelerate the
folio copying.

So in this patch, we refactor the migrate_pages() implementation and
implement the TLB flushing batching.  Base on this, hardware
accelerated folio copying can be implemented.

If too many folios are passed to migrate_pages(), in the naive batched
implementation, we may unmap too many folios at the same time.  The
possibility for a task to wait for the migrated folios to be mapped
again increases.  So the latency may be hurt.  To deal with this
issue, the max number of folios be unmapped in batch is restricted to
no more than HPAGE_PMD_NR in the unit of page.  That is, the influence
is at the same level of THP migration.

We use the following test to measure the performance impact of the
patchset,

On a 2-socket Intel server,

 - Run pmbench memory accessing benchmark

 - Run `migratepages` to migrate pages of pmbench between node 0 and
   node 1 back and forth.

With the patch, the TLB flushing IPI reduces 99.1% during the test and
the number of pages migrated successfully per second increases 291.7%.

This patchset is based on v6.2-rc4.

Changes:

v4:

- Fixed another bug about non-LRU folio migration.  Thanks Hyeonggon!

v3:

- Rebased on v6.2-rc4

- Fixed a bug about non-LRU folio migration.  Thanks Mike!

- Fixed some comments.  Thanks Baolin!

- Collected reviewed-by.

v2:

- Rebased on v6.2-rc3

- Fixed type force cast warning.  Thanks Kees!

- Added more comments and cleaned up the code.  Thanks Andrew, Zi, Alistair, Dan!

- Collected reviewed-by.

from rfc to v1:

- Rebased on v6.2-rc1

- Fix the deadlock issue caused by locking multiple pages synchronously
  per Alistair's comments.  Thanks!

- Fix the autonumabench panic per Rao's comments and fix.  Thanks!

- Other minor fixes per comments. Thanks!

Best Regards,
Huang, Ying