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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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