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    Subject[RFC v7 00/11] Support vrange for anonymous page
    First of all, let's define the term.
    From now on, I'd like to call it as vrange(a.k.a volatile range)
    for anonymous page. If you have a better name in mind, please suggest.

    This version is still *RFC* because it's just quick prototype so
    it doesn't support THP/HugeTLB/KSM and even couldn't build on !x86.
    Before further sorting out issues, I'd like to post current direction
    and discuss it. Of course, I'd like to extend this discussion in
    comming LSF/MM.

    In this version, I changed lots of thing, expecially removed vma-based
    approach because it needs write-side lock for mmap_sem, which will drop
    performance in mutli-threaded big SMP system, KOSAKI pointed out.
    And vma-based approach is hard to meet requirement of new system call by
    John Stultz's suggested semantic for consistent purged handling.

    I tested this patchset with modified jemalloc allocator which was
    leaded by Jason Evans(jemalloc author) who was interest in this feature
    and was happy to port his allocator to use new system call.
    Super Thanks Jason!

    The benchmark for test is ebizzy. It have been used for testing the
    allocator performance so it's good for me. Again, thanks for recommending
    the benchmark, Jason.

    The result is good on my machine (12 CPU, 1.2GHz, DRAM 2G)

    ebizzy -S 20

    jemalloc-vanilla: 52389 records/sec
    jemalloc-vrange: 203414 records/sec

    ebizzy -S 20 with background memory pressure

    jemalloc-vanilla: 40746 records/sec
    jemalloc-vrange: 174910 records/sec

    And it's much improved on KVM virtual machine.

    This patchset is based on v3.9-rc2

    - What's the sys_vrange(addr, length, mode, behavior)?

    It's a hint that user deliver to kernel so kernel can *discard*
    pages in a range anytime. mode is one of VRANGE_VOLATILE and
    VRANGE_NOVOLATILE. VRANGE_NOVOLATILE is memory pin operation so
    kernel coudn't discard any pages any more while VRANGE_VOLATILE
    is memory unpin opeartion so kernel can discard pages in vrange
    anytime. At a moment, behavior is one of VRANGE_FULL and VRANGE
    PARTIAL. VRANGE_FULL tell kernel that once kernel decide to
    discard page in a vrange, please, discard all of pages in a
    vrange selected by victim vrange. VRANGE_PARTIAL tell kernel
    that please discard of some pages in a vrange. But now I didn't
    implemented VRANGE_PARTIAL handling yet.

    - What happens if user access page(ie, virtual address) discarded
    by kernel?

    The user can encounter SIGBUS.

    - What should user do for avoding SIGBUS?
    He should call vrange(addr, length, VRANGE_NOVOLATILE, mode) before
    accessing the range which was called
    vrange(addr, length, VRANGE_VOLATILE, mode)

    - What happens if user access page(ie, virtual address) doesn't
    discarded by kernel?

    The user can see vaild data which was there before calling
    vrange(., VRANGE_VOLATILE) without page fault.

    - What's different with madvise(DONTNEED)?

    System call semantic

    DONTNEED makes sure user always can see zero-fill pages after
    he calls madvise while vrange can see data or encounter SIGBUS.

    Internal implementation

    The madvise(DONTNEED) should zap all mapped pages in range so
    overhead is increased linearly with the number of mapped pages.
    Even, if user access zapped pages as write mode, page fault +
    page allocation + memset should be happened.

    The vrange just register a address range instead of zapping all of pte
    n the vma so it doesn't touch ptes any more.

    - What's the benefit compared to DONTNEED?

    1. The system call overhead is smaller because vrange just registers
    a range using interval tree instead of zapping all the page in a range
    so overhead should be really cheap.

    2. It has a chance to eliminate overheads (ex, zapping pte + page fault
    + page allocation + memset(PAGE_SIZE)) if memory pressure isn't

    3. It has a potential to zap all ptes and free the pages if memory
    pressure is severe so discard scanning overhead could be smaller - TODO

    - What's for targetting?

    Firstly, user-space allocator like ptmalloc, jemalloc or heap management
    of virtual machine like Dalvik. Also, it comes in handy for embedded
    which doesn't have swap device so they can't reclaim anonymous pages.
    By discarding instead of swapout, it could be used in the non-swap system.

    Changelog from v6 - There are many changes.
    * Remove vma-based approach
    * Change system call semantic
    * Add more meaningful experiment

    Changelog from v5 - There are many changes.

    * Working with THP/KSM
    * Remove vma hacking logic in m[no]volatile system call
    * Discard page without swap cache
    * Kswapd discard volatile page so we can discard volatile pages
    although we don't have swap.

    Changelog from v4

    * Add new system call mvolatile/mnovolatile
    * Add sigbus when user try to access volatile range
    * Rebased on v3.7
    * Applied bug fix from John Stultz, Thanks!

    Changelog from v3

    * Removing madvise(addr, length, MADV_NOVOLATILE).
    * add vmstat about the number of discarded volatile pages
    * discard volatile pages without promotion in reclaim path

    Minchan Kim (11):
    vrange: enable generic interval tree
    add vrange basic data structure and functions
    add new system call vrange(2)
    add proc/pid/vrange information
    Add purge operation
    send SIGBUS when user try to access purged page
    keep mm_struct to vrange when system call context
    add LRU handling for victim vrange
    Get rid of depenceny that all pages is from a zone in shrink_page_list
    Purging vrange pages without swap
    add purged page information in vmstat

    arch/x86/include/asm/pgtable_types.h | 2 +
    arch/x86/syscalls/syscall_64.tbl | 1 +
    fs/proc/base.c | 1 +
    fs/proc/internal.h | 6 +
    fs/proc/task_mmu.c | 129 ++++++
    include/asm-generic/pgtable.h | 11 +
    include/linux/mm_types.h | 5 +
    include/linux/rmap.h | 15 +-
    include/linux/swap.h | 1 +
    include/linux/vm_event_item.h | 4 +
    include/linux/vrange.h | 59 +++
    include/uapi/asm-generic/mman-common.h | 5 +
    init/main.c | 2 +
    kernel/fork.c | 3 +
    lib/Makefile | 2 +-
    mm/Makefile | 2 +-
    mm/ksm.c | 2 +-
    mm/memory.c | 24 +-
    mm/rmap.c | 23 +-
    mm/swapfile.c | 36 ++
    mm/vmscan.c | 74 +++-
    mm/vmstat.c | 4 +
    mm/vrange.c | 754 +++++++++++++++++++++++++++++++++
    23 files changed, 1143 insertions(+), 22 deletions(-)
    create mode 100644 include/linux/vrange.h
    create mode 100644 mm/vrange.c


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