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    SubjectRe: [PATCH] anobjrmap 9 priority mjb tree
    >> > This anobjrmap 9 (or anon_mm9) patch adds Rajesh's radix priority search
    >> > tree on top of Martin's 2.6.5-rc3-mjb2 tree, making a priority mjb tree!
    >> > Approximately equivalent to Andrea's 2.6.5-aa1, but using anonmm instead
    >> > of anon_vma, and of course each tree has its own additional features.
    >>
    >> This slows down kernel compile a little, but worse, it slows down SDET
    >> by about 25% (on the 16x). I think you did something horrible to sem
    >> contention ... presumably i_shared_sem, which SDET was fighting with
    >> as it was anyway ;-(
    >>
    >> Diffprofile shows:
    >>
    >> 122626 15.7% total
    >> 44129 790.0% __down
    >> 20988 4.1% default_idle
    >
    > Many thanks for the good news, Martin ;)
    > Looks like I've done something very stupid, perhaps a mismerge.
    > Not found it yet, I'll carry on looking tomorrow.

    I applied Andrew's high sophisticated proprietary semtrace technology.
    The common ones are:

    Call Trace:
    [<c0105aee>] __down+0x96/0x10c
    [<c0118fb8>] default_wake_function+0x0/0x1c
    [<c0105cb8>] __down_failed+0x8/0xc
    [<c014314f>] .text.lock.mmap+0x39/0x12a
    [<c01421a7>] do_mmap_pgoff+0x4cf/0x60c
    [<c010cb74>] old_mmap+0x108/0x144
    [<c025c753>] syscall_call+0x7/0xb

    Which is the vma_link call from do_mmap_pgoff here:

    /* Can addr have changed??
    *
    * Answer: Yes, several device drivers can do it in their
    * f_op->mmap method. -DaveM
    */
    addr = vma->vm_start;

    if (!file || !rb_parent || !vma_merge(mm, prev, rb_parent, addr,
    addr + len, vma->vm_flags, file, pgoff)) {
    vma_link(mm, vma, prev, rb_link, rb_parent);
    if (correct_wcount)
    atomic_inc(&inode->i_writecount);

    vma_link takes i_shared_sem.

    Call Trace:
    [<c0105aee>] __down+0x96/0x10c
    [<c0118fb8>] default_wake_function+0x0/0x1c
    [<c0105cb8>] __down_failed+0x8/0xc
    [<c01431dd>] .text.lock.mmap+0xc7/0x12a
    [<c0142b4c>] do_munmap+0xbc/0x128
    [<c0141f91>] do_mmap_pgoff+0x2b9/0x60c
    [<c010cb74>] old_mmap+0x108/0x144
    [<c025c753>] syscall_call+0x7/0xb

    Is the call to split_vma from do_munmap here:

    /*
    * If we need to split any vma, do it now to save pain later.
    *
    * Note: mremap's move_vma VM_ACCOUNT handling assumes a partially
    * unmapped vm_area_struct will remain in use: so lower split_vma
    * places tmp vma above, and higher split_vma places tmp vma below.
    */
    if (start > mpnt->vm_start) {
    if (split_vma(mm, mpnt, start, 0))
    return -ENOMEM;
    prev = mpnt;
    }

    split_vma takes i_shared_sem, then takes page_table_lock inside it
    (which probably isn't helping either ;-)).

    if (mapping)
    down(&mapping->i_shared_sem);
    spin_lock(&mm->page_table_lock);

    Call Trace:
    [<c0105aee>] __down+0x96/0x10c
    [<c0118fb8>] default_wake_function+0x0/0x1c
    [<c0105cb8>] __down_failed+0x8/0xc
    [<c014311b>] .text.lock.mmap+0x5/0x12a
    [<c0142f79>] exit_mmap+0x191/0x1d0
    [<c011ae84>] mmput+0x50/0x70
    [<c011ec6d>] do_exit+0x1b9/0x330
    [<c011eefa>] do_group_exit+0x9e/0xa0
    [<c011ef0a>] sys_exit_group+0xe/0x14
    [<c025c753>] syscall_call+0x7/0xb

    That's remove_shared_vm_struct calling i_shared_sem

    Call Trace:
    [<c0105aee>] __down+0x96/0x10c
    [<c0118fb8>] default_wake_function+0x0/0x1c
    [<c0105cb8>] __down_failed+0x8/0xc
    [<c014311b>] .text.lock.mmap+0x5/0x12a
    [<c0142694>] unmap_vma+0x44/0x78
    [<c01426dc>] unmap_vma_list+0x14/0x20
    [<c0142ba5>] do_munmap+0x115/0x128
    [<c0141f91>] do_mmap_pgoff+0x2b9/0x60c
    [<c010cb74>] old_mmap+0x108/0x144
    [<c025c753>] syscall_call+0x7/0xb

    That's remove_shared_vm_struct again, but called from unmap_vma this time

    Call Trace:
    [<c0105aee>] __down+0x96/0x10c
    [<c0118fb8>] default_wake_function+0x0/0x1c
    [<c0105cb8>] __down_failed+0x8/0xc
    [<c011c494>] .text.lock.fork+0x79/0x125
    [<c011be5c>] copy_process+0x61c/0xa6c
    [<c011c322>] do_fork+0x76/0x16f
    [<c0105619>] sys_clone+0x29/0x30
    [<c025c753>] syscall_call+0x7/0xb

    That's dup_mmap taking i_shared_sem here:

    /* insert tmp into the share list, just after mpnt */
    down(&file->f_mapping->i_shared_sem);
    __vma_prio_tree_add(tmp, mpnt);
    up(&file->f_mapping->i_shared_sem);

    -
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