Christoph Lameter wrote:
> Provide a way to lock an mm_struct against reclaim (try_to_unmap
> etc). This is necessary for the invalidate notifier approaches so
> that they can reliably add and remove a notifier.
>
> Signed-off-by: Andrea Arcangeli <[EMAIL PROTECTED]>
> Signed-off-by: Christoph Lameter <[EMAIL PROTECTED]>
>
> ---
> include/linux/mm.h | 10 ++++++++
> mm/mmap.c | 66
> +++++++++++++++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 76 insertions(+)
>
> Index: linux-2.6/include/linux/mm.h
> ===================================================================
> --- linux-2.6.orig/include/linux/mm.h 2008-04-02 11:41:47.741678873 -0700
> +++ linux-2.6/include/linux/mm.h 2008-04-04 15:02:17.660504756 -0700
> @@ -1050,6 +1050,16 @@ extern int install_special_mapping(struc
> unsigned long addr, unsigned long len,
> unsigned long flags, struct page **pages);
>
> +/*
> + * Locking and unlocking am mm against reclaim.
> + *
> + * mm_lock will take mmap_sem writably (to prevent additional vmas from being
> + * added) and then take all mapping locks of the existing vmas. With that
> + * reclaim is effectively stopped.
> + */
> +extern void mm_lock(struct mm_struct *mm);
> +extern void mm_unlock(struct mm_struct *mm);
> +
> extern unsigned long get_unmapped_area(struct file *, unsigned long,
> unsigned long, unsigned long, unsigned long);
>
> extern unsigned long do_mmap_pgoff(struct file *file, unsigned long addr,
> Index: linux-2.6/mm/mmap.c
> ===================================================================
> --- linux-2.6.orig/mm/mmap.c 2008-04-04 14:55:03.477593980 -0700
> +++ linux-2.6/mm/mmap.c 2008-04-04 14:59:05.505395402 -0700
> @@ -2242,3 +2242,69 @@ int install_special_mapping(struct mm_st
>
> return 0;
> }
> +
> +static void mm_lock_unlock(struct mm_struct *mm, int lock)
> +{
> + struct vm_area_struct *vma;
> + spinlock_t *i_mmap_lock_last, *anon_vma_lock_last;
> +
> + i_mmap_lock_last = NULL;
> + for (;;) {
> + spinlock_t *i_mmap_lock = (spinlock_t *) -1UL;
> + for (vma = mm->mmap; vma; vma = vma->vm_next)
> + if (vma->vm_file && vma->vm_file->f_mapping &&
>
I think you can break this if() down a bit:
if (!(vma->vm_file && vma->vm_file->f_mapping))
continue;
> + (unsigned long) i_mmap_lock >
> + (unsigned long)
> + &vma->vm_file->f_mapping->i_mmap_lock &&
> + (unsigned long)
> + &vma->vm_file->f_mapping->i_mmap_lock >
> + (unsigned long) i_mmap_lock_last)
> + i_mmap_lock =
> + &vma->vm_file->f_mapping->i_mmap_lock;
>
So this is an O(n^2) algorithm to take the i_mmap_locks from low to high
order? A comment would be nice. And O(n^2)? Ouch. How often is it
called?
And is it necessary to mush lock and unlock together? Unlock ordering
doesn't matter, so you should just be able to have a much simpler loop, no?
> + if (i_mmap_lock == (spinlock_t *) -1UL)
> + break;
> + i_mmap_lock_last = i_mmap_lock;
> + if (lock)
> + spin_lock(i_mmap_lock);
> + else
> + spin_unlock(i_mmap_lock);
> + }
> +
> + anon_vma_lock_last = NULL;
> + for (;;) {
> + spinlock_t *anon_vma_lock = (spinlock_t *) -1UL;
> + for (vma = mm->mmap; vma; vma = vma->vm_next)
> + if (vma->anon_vma &&
> + (unsigned long) anon_vma_lock >
> + (unsigned long) &vma->anon_vma->lock &&
> + (unsigned long) &vma->anon_vma->lock >
> + (unsigned long) anon_vma_lock_last)
> + anon_vma_lock = &vma->anon_vma->lock;
> + if (anon_vma_lock == (spinlock_t *) -1UL)
> + break;
> + anon_vma_lock_last = anon_vma_lock;
> + if (lock)
> + spin_lock(anon_vma_lock);
> + else
> + spin_unlock(anon_vma_lock);
> + }
> +}
>
> +
> +/*
> + * This operation locks against the VM for all pte/vma/mm related
> + * operations that could ever happen on a certain mm. This includes
> + * vmtruncate, try_to_unmap, and all page faults. The holder
> + * must not hold any mm related lock. A single task can't take more
> + * than one mm lock in a row or it would deadlock.
> + */
> +void mm_lock(struct mm_struct * mm)
> +{
> + down_write(&mm->mmap_sem);
> + mm_lock_unlock(mm, 1);
> +}
> +
> +void mm_unlock(struct mm_struct *mm)
> +{
> + mm_lock_unlock(mm, 0);
> + up_write(&mm->mmap_sem);
> +}
>
>
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