Re: [PATCHv7 00/29] THP-enabled tmpfs/shmem using compound pages

From: Shi, Yang
Date: Mon Apr 18 2016 - 18:56:00 EST

Hi Kirill,

Finally, I got some time to look into and try yours and Hugh's patches, got two problems.

1. A quick boot up test on my ARM64 machine with your v7 tree shows some unexpected error:

systemd-journald[285]: Failed to save stream data /run/systemd/journal/streams/8:16863: No space left on device
systemd-journald[285]: Failed to save stream data /run/systemd/journal/streams/8:16865: No space left on device
Starting DNS forwarder and DHCP server.systemd-journald[285]: Failed to save stream data /run/systemd/journal/streams/8:16867: No space left on device
systemd-journald[285]: Failed to save stream data /run/systemd/journal/streams/8:16869: No space left on device
Starting Postfix Mail Transport Agent...
systemd-journald[285]: Failed to save stream data /run/systemd/journal/streams/8:16871: No space left on device
Starting Berkeley Internet Name Domain (DNS)...
Starting Wait for Network to be Configured...
systemd-journald[285]: Failed to save stream data /run/systemd/journal/streams/8:2422: No space left on device
[ OK ] Started /etc/rc.local Compatibility.
[FAILED] Failed to start DNS forwarder and DHCP server.
See 'systemctl status dnsmasq.service' for details.
systemd-journald[285]: Failed to save stream data /run/systemd/journal/streams/8:2425: No space left on device
[ OK ] Started Serial Getty on ttyS1.
[ OK ] Started Serial Getty on ttyS0.
[ OK ] Started Getty on tty1.
systemd-journald[285]: Failed to save stream data /run/systemd/journal/streams/8:2433: No space left on device
[FAILED] Failed to start Berkeley Internet Name Domain (DNS).
See 'systemctl status named.service' for details.

The /run dir is mounted as tmpfs.

x86 boot doesn't get such error. And, Hugh's patches don't have such problem.

2. I ran my THP test (generated a program with 4MB text section) on both x86-64 and ARM64 with yours and Hugh's patches (linux-next tree), I got the program execution time reduced by ~12% on x86-64, it looks very impressive.

But, on ARM64, there is just ~3% change, and sometimes huge tmpfs may show even worse data than non-hugepage.

Both yours and Hugh's patches has the same behavior.

Any idea?


On 4/15/2016 5:23 PM, Kirill A. Shutemov wrote:
This is probably the last update before the mm summit. Main forcus is on
khugepaged stability.

khugepaged is in more reasonable shape now. I missed quite a few corner
cases on first try. I run this version via LTP, trinity and syzkaller
without crashes so far.

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:// hugetmpfs/v7

== Changelog ==

- 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();

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

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

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

- huge= mountoption now can have values always, within_size, advice and
- 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

- 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.

== Patchset overview ==

Update documentation on THP vs. mlock. I've posted it separately
before. It can go in.

Rework fault path and rmap to handle file pmd. Unlike DAX with
vm_ops->pmd_fault, we don't need to ask filesystem twice -- first
for huge page and then for small. If ->fault happened to return
huge page and VMA is suitable for mapping it as huge, we would
do so.
Add support for huge file pages in rmap;

Various preparation of THP core for file pages.

Various preparation of MM core for file pages.

And finally, bring huge pages into tmpfs/shmem.

Wire up madvise() existing hints for file THP.
We can implement fadvise() later.

Documentation update.

Extend khugepaged to support shmem/tmpfs.
Hugh Dickins (1):
shmem: get_unmapped_area align huge page

Kirill A. Shutemov (28):
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()
khugepaged: add support of collapse for tmpfs/shmem pages

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 | 29 +-
include/linux/userfaultfd_k.h | 8 +-
include/linux/vm_event_item.h | 7 +
include/trace/events/huge_memory.h | 3 +-
ipc/shm.c | 6 +-
lib/radix-tree.c | 68 +-
mm/Makefile | 2 +-
mm/filemap.c | 226 ++--
mm/gup.c | 7 +-
mm/huge_memory.c | 2028 ++++++----------------------------
mm/internal.h | 4 +-
mm/khugepaged.c | 1772 +++++++++++++++++++++++++++++
mm/ksm.c | 5 +-
mm/memory.c | 859 +++++++-------
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 | 689 ++++++++++--
mm/swap.c | 2 +
mm/truncate.c | 22 +-
mm/util.c | 6 +
mm/vmscan.c | 6 +
mm/vmstat.c | 4 +
74 files changed, 3919 insertions(+), 2395 deletions(-)
create mode 100644 mm/khugepaged.c