[PATCHv8 00/32] THP-enabled tmpfs/shmem using compound pages

Kirill A. Shutemov
2016-05-12T15:50:05Z

This update aimed to address my todo list from lsf/mm summit:

- we now able to recovery memory by splitting huge pages partly beyond
i_size. This should address concern about small files.

- bunch of bug fixes for khugepaged, including fix for data corruption
reported by Hugh.

- Disabled for Power as it requires deposited page table to get THP
mapped and we don't do deposit/withdraw for file THP.

The main part of patchset (up to khugepaged stuff) is relatively stable --
I fixed few minor bugs there, but nothing major.

I would appreciate rigorous review of khugepaged and code to split huge
pages under memory pressure.

The patchset is on top of v4.6-rc3 plus Hugh's "easy preliminaries to
THPagecache" and Ebru's khugepaged swapin patches form -mm tree.

Git tree:

git://git.kernel.org/pub/scm/linux/kernel/git/kas/linux.git hugetmpfs/v8

== Changelog ==

v8:
- khugepaged updates:
+ mark collapsed page dirty, otherwise vmscan would discard it;
+ account pages to mapping->nrpages on shmem_charge;
+ fix a situation when not all tail pages put on radix tree on collapse;
+ fix off-by-one in loop-exit condition in khugepaged_scan_shmem();
+ use radix_tree_iter_next/radix_tree_iter_retry instead of gotos;
+ fix build withount CONFIG_SHMEM (again);
- split huge pages beyond i_size under memory pressure;
- disable huge tmpfs on Power, as it makes use of deposited page tables,
we don't have;
- fix filesystem size limit accouting;
- mark page referenced on split_huge_pmd() if the pmd is young;
- uncharge pages from shmem, removed during split_huge_page();
- make shmem_inode_info::lock irq-safe -- required by khugepaged;

v7:
- khugepaged updates:
+ fix page leak/page cache corruption on collapse fail;
+ filter out VMAs not suitable for huge pages due misaligned vm_pgoff;
+ fix build without CONFIG_SHMEM;
+ drop few over-protective checks;
- fix bogus VM_BUG_ON() in __delete_from_page_cache();

v6:
- experimental collapse support;
- fix swapout mapped huge pages;
- fix page leak in faularound code;
- fix exessive huge page allocation with huge=within_size;
- rename VM_NO_THP to VM_NO_KHUGEPAGED;
- fix condition in hugepage_madvise();
- accounting reworked again;

v5:
- add FileHugeMapped to /proc/PID/smaps;
- make FileHugeMapped in meminfo aligned with other fields;
- Documentation/vm/transhuge.txt updated;

v4:
- first four patch were applied to -mm tree;
- drop pages beyond i_size on split_huge_pages;
- few small random bugfixes;

v3:
- huge= mountoption now can have values always, within_size, advice and
never;
- sysctl handle is replaced with sysfs knob;
- MADV_HUGEPAGE/MADV_NOHUGEPAGE is now respected on page allocation via
page fault;
- mlock() handling had been fixed;
- bunch of smaller bugfixes and cleanups.

== Design overview ==

Huge pages are allocated by shmem when it's allowed (by mount option) and
there's no entries for the range in radix-tree. Huge page is represented by
HPAGE_PMD_NR entries in radix-tree.

MM core maps a page with PMD if ->fault() returns huge page and the VMA is
suitable for huge pages (size, alignment). There's no need into two
requests to file system: filesystem returns huge page if it can,
graceful fallback to small pages otherwise.

As with DAX, split_huge_pmd() is implemented by unmapping the PMD: we can
re-fault the page with PTEs later.

Basic scheme for split_huge_page() is the same as for anon-THP.
Few differences:

- File pages are on radix-tree, so we have head->_count offset by
HPAGE_PMD_NR. The count got distributed to small pages during split.

- mapping->tree_lock prevents non-lockless access to pages under split
over radix-tree;

- Lockless access is prevented by setting the head->_count to 0 during
split, so get_page_unless_zero() would fail;

- After split, some pages can be beyond i_size. We drop them from
radix-tree.

- We don't setup migration entries. Just unmap pages. It helps
handling cases when i_size is in the middle of the page: no need
handle unmap pages beyond i_size manually.

COW mapping handled on PTE-level. It's not clear how beneficial would be
allocation of huge pages on COW faults. And it would require some code to
make them work.

I think at some point we can consider teaching khugepaged to collapse
pages in COW mappings, but allocating huge on fault is probably overkill.

As with anon THP, we mlock file huge page only if it mapped with PMD.
PTE-mapped THPs are never mlocked. This way we can avoid all sorts of
scenarios when we can leak mlocked page.

As with anon THP, we split huge page on swap out.

Truncate and punch hole that only cover part of THP range is implemented
by zero out this part of THP.

This have visible effect on fallocate(FALLOC_FL_PUNCH_HOLE) behaviour.
As we don't really create hole in this case, lseek(SEEK_HOLE) may have
inconsistent results depending what pages happened to be allocated.
I don't think this will be a problem.

We track per-super_block list of inodes which potentially have huge page
partly beyond i_size. Under memory pressure or if we hit -ENOSPC, we split
such pages in order to recovery memory.

The list is per-sb, as we need to split a page from our filesystem if hit
-ENOSPC (-o size= limit) during shmem_getpage_gfp() to free some space.

Hugh Dickins (1):
shmem: get_unmapped_area align huge page

Kirill A. Shutemov (31):
thp, mlock: update unevictable-lru.txt
mm: do not pass mm_struct into handle_mm_fault
mm: introduce fault_env
mm: postpone page table allocation until we have page to map
rmap: support file thp
mm: introduce do_set_pmd()
thp, vmstats: add counters for huge file pages
thp: support file pages in zap_huge_pmd()
thp: handle file pages in split_huge_pmd()
thp: handle file COW faults
thp: skip file huge pmd on copy_huge_pmd()
thp: prepare change_huge_pmd() for file thp
thp: run vma_adjust_trans_huge() outside i_mmap_rwsem
thp: file pages support for split_huge_page()
thp, mlock: do not mlock PTE-mapped file huge pages
vmscan: split file huge pages before paging them out
page-flags: relax policy for PG_mappedtodisk and PG_reclaim
radix-tree: implement radix_tree_maybe_preload_order()
filemap: prepare find and delete operations for huge pages
truncate: handle file thp
mm, rmap: account shmem thp pages
shmem: prepare huge= mount option and sysfs knob
shmem: add huge pages support
shmem, thp: respect MADV_{NO,}HUGEPAGE for file mappings
thp: update Documentation/vm/transhuge.txt
thp: extract khugepaged from mm/huge_memory.c
khugepaged: move up_read(mmap_sem) out of khugepaged_alloc_page()
shmem: make shmem_inode_info::lock irq-safe
khugepaged: add support of collapse for tmpfs/shmem pages
thp: introduce CONFIG_TRANSPARENT_HUGE_PAGECACHE
shmem: split huge pages beyond i_size under memory pressure

Documentation/filesystems/Locking | 10 +-
Documentation/vm/transhuge.txt | 130 ++-
Documentation/vm/unevictable-lru.txt | 21 +
arch/alpha/mm/fault.c | 2 +-
arch/arc/mm/fault.c | 2 +-
arch/arm/mm/fault.c | 2 +-
arch/arm64/mm/fault.c | 2 +-
arch/avr32/mm/fault.c | 2 +-
arch/cris/mm/fault.c | 2 +-
arch/frv/mm/fault.c | 2 +-
arch/hexagon/mm/vm_fault.c | 2 +-
arch/ia64/mm/fault.c | 2 +-
arch/m32r/mm/fault.c | 2 +-
arch/m68k/mm/fault.c | 2 +-
arch/metag/mm/fault.c | 2 +-
arch/microblaze/mm/fault.c | 2 +-
arch/mips/mm/fault.c | 2 +-
arch/mn10300/mm/fault.c | 2 +-
arch/nios2/mm/fault.c | 2 +-
arch/openrisc/mm/fault.c | 2 +-
arch/parisc/mm/fault.c | 2 +-
arch/powerpc/mm/copro_fault.c | 2 +-
arch/powerpc/mm/fault.c | 2 +-
arch/s390/mm/fault.c | 2 +-
arch/score/mm/fault.c | 2 +-
arch/sh/mm/fault.c | 2 +-
arch/sparc/mm/fault_32.c | 4 +-
arch/sparc/mm/fault_64.c | 2 +-
arch/tile/mm/fault.c | 2 +-
arch/um/kernel/trap.c | 2 +-
arch/unicore32/mm/fault.c | 2 +-
arch/x86/mm/fault.c | 2 +-
arch/xtensa/mm/fault.c | 2 +-
drivers/base/node.c | 13 +-
drivers/char/mem.c | 24 +
drivers/iommu/amd_iommu_v2.c | 3 +-
drivers/iommu/intel-svm.c | 2 +-
fs/proc/meminfo.c | 7 +-
fs/proc/task_mmu.c | 10 +-
fs/userfaultfd.c | 22 +-
include/linux/huge_mm.h | 36 +-
include/linux/khugepaged.h | 6 +
include/linux/mm.h | 51 +-
include/linux/mmzone.h | 4 +-
include/linux/page-flags.h | 19 +-
include/linux/radix-tree.h | 1 +
include/linux/rmap.h | 2 +-
include/linux/shmem_fs.h | 45 +-
include/linux/userfaultfd_k.h | 8 +-
include/linux/vm_event_item.h | 7 +
include/trace/events/huge_memory.h | 3 +-
ipc/shm.c | 10 +-
lib/radix-tree.c | 68 +-
mm/Kconfig | 8 +
mm/Makefile | 2 +-
mm/filemap.c | 226 ++--
mm/gup.c | 7 +-
mm/huge_memory.c | 2032 ++++++----------------------------
mm/internal.h | 4 +-
mm/khugepaged.c | 1851 +++++++++++++++++++++++++++++++
mm/ksm.c | 5 +-
mm/memory.c | 860 +++++++-------
mm/mempolicy.c | 4 +-
mm/migrate.c | 5 +-
mm/mmap.c | 26 +-
mm/nommu.c | 3 +-
mm/page-writeback.c | 1 +
mm/page_alloc.c | 21 +
mm/rmap.c | 78 +-
mm/shmem.c | 918 +++++++++++++--
mm/swap.c | 2 +
mm/truncate.c | 22 +-
mm/util.c | 6 +
mm/vmscan.c | 6 +
mm/vmstat.c | 4 +
75 files changed, 4240 insertions(+), 2415 deletions(-)
create mode 100644 mm/khugepaged.c

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2.8.1