[PATCH v2 0/1] change ->index to PAGE_SIZE for hugetlb pages

From: Sidhartha Kumar
Date: Mon Jul 10 2023 - 19:06:03 EST

========================== OVERVIEW ========================================
This patchset attempts to implement a listed filemap TODO which is
changing hugetlb folios to have ->index in PAGE_SIZE. This simplifies many
functions within filemap.c as they have to special case hugetlb pages.
>From the RFC v1[1], Mike pointed out that hugetlb will still have to maintain
a huge page sized index as it is used for the reservation map and the hash
function for the hugetlb mutex table.

This patchset adds new wrappers for hugetlb code to to interact with the
page cache. These wrappers calculate a linear page index as this is now
what the page cache expects for hugetlb pages.

>From the discussion on HGM for hugetlb[3], there is a want to remove hugetlb
special casing throughout the core mm code. This series accomplishes
a part of this by shifting complexity from filemap.c to hugetlb.c. There
are still checks for hugetlb within the filemap code as cgroup accounting
and hugetlb accounting are special cased as well.

=========================== PERFORMANCE =====================================
6.4.0-rc5
@hugetlb_add_to_page_cache:
[512, 1K) 7518 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@|
[1K, 2K) 158 |@ |
[2K, 4K) 30 | |
[4K, 8K) 6 | |
[8K, 16K) 9 |

6.5.0-rc1 + this patch series
@hugetlb_add_to_page_cache:
[512, 1K) 6345 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@|
[1K, 2K) 1308 |@@@@@@@@@@ |
[2K, 4K) 39 | |
[4K, 8K) 20 | |
[8K, 16K) 8 | |
[16K, 32K) 1 | |

6.4.0-rc5
@__filemap_get_folio:
[256, 512) 11292 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@|
[512, 1K) 4615 |@@@@@@@@@@@@@@@@@@@@@ |
[1K, 2K) 960 |@@@@ |
[2K, 4K) 188 | |
[4K, 8K) 68 | |
[8K, 16K) 14 | |
[16K, 32K) 4 | |
[2G, 4G) 4 | |

6.5.0-rc1 + this patch series
@__filemap_get_folio:
@get_folio_ns:
[128, 256) 13 | |
[256, 512) 11131 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@|
[512, 1K) 5544 |@@@@@@@@@@@@@@@@@@@@@@@@@ |
[1K, 2K) 996 |@@@@ |
[2K, 4K) 317 |@ |
[4K, 8K) 76 | |
[8K, 16K) 23 | |
[16K, 32K) 6 | |
[32K, 64K) 1 | |
[64K, 128K) 0 | |
[128K, 256K) 0 | |
[256K, 512K) 0 | |
[512K, 1M) 0 | |
[1M, 2M) 0 | |
[2M, 4M) 0 | |
[4M, 8M) 0 | |
[8M, 16M) 0 | |
[16M, 32M) 0 | |
[32M, 64M) 0 | |
[64M, 128M) 0 | |
[128M, 256M) 0 | |
[256M, 512M) 0 | |
[512M, 1G) 0 | |
[1G, 2G) 0 | |
[2G, 4G) 3 |

=========================== TESTING ==========================================
This series passes the LTP hugetlb test cases as well as the libhugetlbfs tests.

********** TEST SUMMARY
* 2M
* 32-bit 64-bit
* Total testcases: 110 113
* Skipped: 0 0
* PASS: 107 113
* FAIL: 0 0
* Killed by signal: 3 0
* Bad configuration: 0 0
* Expected FAIL: 0 0
* Unexpected PASS: 0 0
* Test not present: 0 0
* Strange test result: 0 0
**********



RFC v2[2]-> v1:
-cleanup code style

RFC v1 -> v2
-change direction of series to maintain both huge and base page size index
rather than try to get rid of all references to a huge page sized index.

v1 -> v2
- squash seperate filemap and hugetlb patches into one to allow for bisection
per Matthew
- get rid of page_to_index()
- fix errors in hugetlb_fallocate() and remove_inode_hugepages()


rebased on 07/10/2023 mm-unstable


Sidhartha Kumar (1):
mm/filemap: remove hugetlb special casing in filemap.c

fs/hugetlbfs/inode.c | 10 +++++-----
include/linux/hugetlb.h | 12 ++++++++++++
include/linux/pagemap.h | 26 ++------------------------
mm/filemap.c | 36 +++++++++++-------------------------
mm/hugetlb.c | 11 ++++++-----
5 files changed, 36 insertions(+), 59 deletions(-)

--
2.41.0