[PATCH 0/7] begin converting hugetlb code to folios

[Sidhartha Kumar <sidhartha.kumar@oracle.com>]

This patch series starts the conversion of the hugetlb code to operate
on struct folios rather than struct pages. This removes the ambiguitiy
of whether functions are operating on head pages, tail pages of compound
pages, or base pages. 

This series passes the linux test project hugetlb test cases.

Patch 1 adds hugeltb specific page macros that can operate on folios.

Patch 2 adds the private field of the first tail page to struct page.
This patch depends on Matthew Wilcox's patch mm: Add the first tail
page to struct folio[1]:

Patchs 3-4 introduce hugetlb subpool helper functions which operate on
struct folios. These patches were tested using the hugepage-mmap.c
selftest along with the migratepages command.

Patch 5 converts hugetlb_delete_from_page_cache() to use folios.
This patch depends on Mike Kravetz's patch: hugetlb: rename 
remove_huge_page to hugetlb_delete_from_page_cache[2]:


Patch 6 adds a folio_hstate() function to get hstate information from a
folio.

Patch 7 adds a user of folio_hstate().

Bpftrace was used to track time spent in the free_huge_pages function
during the ltp test cases as it is a caller of the hugetlb subpool
functions. From the histogram, the performance is similar before and
after the patch series. 

Time spent in 'free_huge_page'

6.0.0-rc2.master.20220823
@nsecs:
[256, 512)         14770 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@|
[512, 1K)            155 |                                                    |
[1K, 2K)             169 |                                                    |
[2K, 4K)              50 |                                                    |
[4K, 8K)              14 |                                                    |
[8K, 16K)              3 |                                                    |
[16K, 32K)             3 |                                                    |


6.0.0-rc2.master.20220823 + patch series
@nsecs: 
[256, 512)         13678 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@|
[512, 1K)            142 |                                                    |
[1K, 2K)             199 |                                                    |
[2K, 4K)              44 |                                                    |
[4K, 8K)              13 |                                                    |
[8K, 16K)              4 |                                                    |
[16K, 32K)             1 |                                                    |

[1] https://lore.kernel.org/linux-mm/20220808193430.3378317-6-willy@infradead.org/
[2] https://lore.kernel.org/all/20220824175757.20590-4-mike.kravetz@oracle.com/T/#me431952361ea576862d7eb617a5dced9807dbabb

Sidhartha Kumar (7):
  mm/hugetlb: add folio support to hugetlb specific flag macros
  mm: add private field of first tail to struct page and struct folio
  mm/hugetlb: add hugetlb_folio_subpool() helper
  mm/hugetlb: add hugetlb_set_folio_subpool() helper
  mm/hugetlb: convert hugetlb_delete_from_page_cache() to use folios
  mm/hugetlb add folio_hstate()
  mm/migrate: use folio_hstate() in alloc_migration_target()

 fs/hugetlbfs/inode.c     | 22 ++++++++++----------
 include/linux/hugetlb.h  | 45 ++++++++++++++++++++++++++++++++++++----
 include/linux/mm_types.h | 15 ++++++++++++++
 mm/migrate.c             |  2 +-
 4 files changed, 68 insertions(+), 16 deletions(-)

-- 
2.31.1