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. To help the tests of splitting huge pages, 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) splitting PMD THPs, 2) splitting PTE-mapped THPs, 3) splitting pagecache THPs to any lower order, 4) truncating a pagecache THP to a page with a lower order, and 5) punching holes in a pagecache THP to cause splitting THPs to lower order THPs. The patchset is on top of Matthew's pagecache/next tree[3]. * Patch 1 is cherry-picked from Matthew's recent xarray fix [4] just to make sure Patch 3 to 7 can run without problem. I let Matthew decide how it should get picked up. * Patch 2 is self-contained and can be merged if it looks OK. Comments and/or suggestions are welcome. ChangeLog === >From RFC: 1. Fixed debugfs to handle splitting PTE-mapped THPs properly and added stats for split THPs. 2. Added a new test case for splitting PTE-mapped THPs. Each of the four PTEs points to a different subpage from four THPs and used kpageflags to check whether a PTE points to a THP or not (AnonHugePages from smap does not show PTE-mapped THPs). 3. mem_cgroup_split_huge_fixup() takes order instead of nr. 4. split_page_owner takes old_order and new_order instead of nr and new_order. 5. Corrected __split_page_owner declaration and fixed its implementation when splitting a THP to a new order. 6. Renamed left to remaining in truncate_inode_partial_page(). 7. Use VM_BUG_ON instead of WARN_ONCE when splitting a THP to the unsupported order-0 and splitting anonymous THPs to non-zero orders. 8. Added punching holes in a file as a new pagecache THP split test case, which uncovered an xarray bug. [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 [4] https://git.infradead.org/users/willy/xarray.git Matthew Wilcox (Oracle) (1): XArray: Fix splitting to non-zero orders 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: 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 | 10 +- lib/test_xarray.c | 26 +- lib/xarray.c | 4 +- mm/huge_memory.c | 219 ++++++-- mm/internal.h | 1 + mm/memcontrol.c | 6 +- mm/migrate.c | 2 +- mm/page_alloc.c | 2 +- mm/page_owner.c | 13 +- mm/swap.c | 1 - mm/truncate.c | 29 +- tools/testing/selftests/vm/.gitignore | 1 + tools/testing/selftests/vm/Makefile | 1 + .../selftests/vm/split_huge_page_test.c | 479 ++++++++++++++++++ 16 files changed, 742 insertions(+), 65 deletions(-) create mode 100644 tools/testing/selftests/vm/split_huge_page_test.c -- 2.28.0
