From: Zi Yan <ziy@xxxxxxxxxx> Hi all, With Matthew's THP in pagecache patches[1], we will be able to handle any size pagecache THPs, but currently split_huge_page can only split a THP to order-0 pages. This can easily erase the benefit of having pagecache THPs, when operations like truncate might want to keep pages larger than order-0. In response, here is the patches to add support for splitting a THP to any lower order pages. In addition, this patchset prepares for my PUD THP patchset[2], since splitting a PUD THP to multiple PMD THPs can be handled by split_huge_page_to_list_to_order function added by this patchset, which reduces a lot of redundant code without just replicating split_huge_page for PUD THP. The patchset is on top of Matthew's pagecache/next tree[3]. To ease the tests of split_huge_page functions, I added a new debugfs interface at <debugfs>/split_huge_pages_in_range_pid, so developers can split THPs in a given range from a process with the given pid by writing "<pid>,<vaddr_start>,<vaddr_end>,<to_order>" to the interface. I also added a new test program to test 1) split PMD THPs, 2) split pagecache THPs to any lower order, and 3) truncating a pagecache THP to a page with a lower order. Suggestions and comments are welcome. Thanks. [1] https://lore.kernel.org/linux-mm/20201029193405.29125-1-willy@xxxxxxxxxxxxx/ [2] https://lore.kernel.org/linux-mm/20200928175428.4110504-1-zi.yan@xxxxxxxx/ [3] https://git.infradead.org/users/willy/pagecache.git/shortlog/refs/heads/next Zi Yan (6): mm: huge_memory: add new debugfs interface to trigger split huge page on any page range. mm: memcg: make memcg huge page split support any order split. mm: page_owner: add support for splitting to any order in split page_owner. mm: thp: add support for split huge page to any lower order pages. mm: truncate: split thp to a non-zero order if possible. mm: huge_memory: enable debugfs to split huge pages to any order. include/linux/huge_mm.h | 8 + include/linux/memcontrol.h | 5 +- include/linux/page_owner.h | 7 +- mm/huge_memory.c | 177 ++++++++++-- mm/internal.h | 1 + mm/memcontrol.c | 4 +- mm/migrate.c | 2 +- mm/page_alloc.c | 2 +- mm/page_owner.c | 6 +- mm/swap.c | 1 - mm/truncate.c | 22 +- tools/testing/selftests/vm/Makefile | 1 + .../selftests/vm/split_huge_page_test.c | 255 ++++++++++++++++++ 13 files changed, 453 insertions(+), 38 deletions(-) create mode 100644 tools/testing/selftests/vm/split_huge_page_test.c -- 2.28.0
