On Sun, 18 Mar 2001, Manfred Spraul wrote:
> > The problem is that mmap_sem seems to be protecting the list
> > of VMAs, so taking _only_ the page_table_lock could let a VMA
> > change under us while a page fault is underway ...
>
> No, that can't happen.
> VMA changes only happen if both the mmap_sem and the page table lock is
> acquired. (check insert_vm() at the end of mm/mmap.c)
> The page fault path uses the map_sem, kswaps uses page_table_lock.
You're right here, I missed this "little detail"...
> << from your patch:
> --- linux-2.4.2-ac20-vm/mm/vmscan.c.orig Sat Mar 17 11:30:49 2001
> +++ linux-2.4.2-ac20-vm/mm/vmscan.c Sat Mar 17 20:53:10 2001
> @@ -231,6 +231,7 @@
> * Find the proper vm-area after freezing the vma chain
> * and ptes.
> */
> + down_read(&mm->mmap_sem);
> spin_lock(&mm->page_table_lock);
> >>>>
>
> Why do you acquire the mmap semaphore in swapout_mm()? The old rule was
> that kswapd should never sleep on the mmap semaphore. Isn't there a
> deadlock if mmap sem is already acquired? I don't remember the details.
You're right, kswapd shouldn't do this. I have this removed from
my code right now...
> > The problem is that mmap_sem seems to be protecting the list
> > of VMAs, so taking _only_ the page_table_lock could let a VMA
> > change under us while a page fault is underway ...
>
> I remember that the pmd_alloc() and pte_alloc() functions need
> additional locking.
Isn't this what the page_table_lock is for ?
(too bad they're not using it...)
regards,
Rik
-- Virtual memory is like a game you can't win; However, without VM there's truly nothing to lose...http://www.surriel.com/ http://www.conectiva.com/ http://distro.conectiva.com.br/
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This archive was generated by hypermail 2b29 : Fri Mar 23 2001 - 21:00:11 EST