[PATCH v4 0/5] begin converting hugetlb code to folios

[Sidhartha Kumar]

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.
For 32-bit, _private_1 alinging with page[1].private was confirmed by
using pahole. This patch depends on Matthew Wilcox's patch mm: Add the first tail
page to struct folio[1]:

Patch 3 introduces 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 4 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 5 adds a folio_hstate() function to get hstate information from a
folio and 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://kernel.googlesource.com/pub/scm/linux/kernel/git/next/linux-next/+/f0a284d27efbfcc1a46c2a6075a259e628ad29c0
[2] https://kernel.googlesource.com/pub/scm/linux/kernel/git/next/linux-next/+/e829be3202116d9aeb94cc1ff64e89dcbf7c47d3

v3 -> v4:
- rebase on next-20220921
- collect reviews by Mike Kravetz
- squash patches 3 and 4 from v2
- remove delete_from_page_cache()
v2 -> v3:
- fix build error by defining folio_hsate() when CONFIG_HUGETLB_PAGE=n
v1 --> v2:
- test compiling on i386.
- change return type from int to bool in patch 1
- move _private_1 field in struct page to within a CONFIG_64BIT block in patch 2
- squash patch 7 from v1 into patch 6

Sidhartha Kumar (5):
  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() helpers
  hugetlbfs: convert hugetlb_delete_from_page_cache() to use folios
  mm/hugetlb: add folio_hstate()

 fs/hugetlbfs/inode.c     | 22 ++++++++---------
 include/linux/hugetlb.h  | 53 +++++++++++++++++++++++++++++++++++++---
 include/linux/mm_types.h | 14 +++++++++++
 include/linux/pagemap.h  |  1 -
 mm/folio-compat.c        |  5 ----
 mm/migrate.c             |  2 +-
 6 files changed, 75 insertions(+), 22 deletions(-)

-- 
2.31.1