Messages in this thread | | | Date | Fri, 09 Apr 2004 15:56:51 -0700 | From | "Martin J. Bligh" <> | Subject | Re: [PATCH] anobjrmap 9 priority mjb tree |
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>> > 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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