[PATCH 00/13] mm/munlock: rework of mlock+munlock page handling

[Hugh Dickins]

I wondered whether to post this munlocking rework in
https://lore.kernel.org/linux-mm/35c340a6-96f-28a0-2b7b-2f9fbddc01f@xxxxxxxxxx/

There the discussion was OOM reaping, but the main reason for the rework
has been catastrophic contention on i_mmap_rwsem when exiting from
multiply mlocked files; and frustration with how contorted munlocking is.

Here it is based on 5.17-rc2, applies also to -rc3, almost cleanly to
mmotm 2022-02-03-21-58 (needs two easy fixups in mm/huge_memory.c); but
likely to conflict (I hope not fundamentally) with several concurrent
large patchsets.

tl;dr
 mm/mlock.c  |  634 +++++++++++++++-----------------------
 23 files changed, 510 insertions(+), 779 deletions(-)

In my own opinion, this is ready to go in: that whatever its defects,
it's a big practical improvement over what's presently there.  Others
may differ; and it may be too much to arrive at a quick opinion on.
My hope is that it will strike a chord with some who have laboured in
this area in the past: I'll be short of time to do much more with it,
so maybe someone else could take over if necessary.

At present there's no update to Documentation/vm/unevictable-lru.rst:
that always needs a different mindset, can follow later, please refer
to commit messages for now.

There are two half-related mm/thp patches at the end: enhancements
we've had for a long time, but more suited after the mlock changes.

01/13 mm/munlock: delete page_mlock() and all its works
02/13 mm/munlock: delete FOLL_MLOCK and FOLL_POPULATE gupflags
03/13 mm/munlock: delete munlock_vma_pages_all(), allow oomreap
04/13 mm/munlock: rmap call mlock_vma_page() munlock_vma_page()
05/13 mm/munlock: replace clear_page_mlock() by final clearance
06/13 mm/munlock: maintain page->mlock_count while unevictable
07/13 mm/munlock: mlock_pte_range() when mlocking or munlocking
08/13 mm/migrate: __unmap_and_move() push good newpage to LRU
09/13 mm/munlock: delete smp_mb() from __pagevec_lru_add_fn()
10/13 mm/munlock: mlock_page() munlock_page() batch by pagevec
11/13 mm/munlock: page migration needs mlock pagevec drained
12/13 mm/thp: collapse_file() do try_to_unmap(TTU_BATCH_FLUSH)
13/13 mm/thp: shrink_page_list() avoid splitting VM_LOCKED THP

 include/linux/mm.h        |    2 
 include/linux/mm_inline.h |   11 
 include/linux/mm_types.h  |   19 +
 include/linux/rmap.h      |   23 -
 kernel/events/uprobes.c   |    7 
 mm/gup.c                  |   43 --
 mm/huge_memory.c          |   55 ---
 mm/hugetlb.c              |    4 
 mm/internal.h             |   64 ++-
 mm/khugepaged.c           |   14 
 mm/ksm.c                  |   12 
 mm/madvise.c              |    5 
 mm/memcontrol.c           |    3 
 mm/memory.c               |   45 --
 mm/migrate.c              |   42 +-
 mm/mlock.c                |  634 +++++++++++++++-----------------------
 mm/mmap.c                 |   32 -
 mm/mmzone.c               |    7 
 mm/oom_kill.c             |    2 
 mm/rmap.c                 |  156 ++-------
 mm/swap.c                 |   89 ++---
 mm/userfaultfd.c          |   14 
 mm/vmscan.c               |    6 
 23 files changed, 510 insertions(+), 779 deletions(-)

Hugh