Re: Atomic operation for physically moving a page (for memory defragmentation)

[IWAMOTO Toshihiro <iwamoto@valinux.co.jp>]

At Wed, 23 Jun 2004 13:56:30 -0700,
Dave Hansen wrote:
> 
> On Wed, 2004-06-23 at 04:59, Hirokazu Takahashi wrote:
> > We should know that many part of kernel code will access the page
> > without holding a lock_page(). The lock_page() can't block them.
> 
> No, but it will block them from establishing a new PTE to the page.  You
> need to:
> 
> 1. make sure no new PTEs can be established to the page
> 2. make sure there are no valid PTEs to the page.
> 3. do the move
> 
> My suggestion relates to 1, only.

I wonder if you are talking exclusively about swap (anonymous) pages,
where lock_page() might work.

(I wonder why lock_page() is needed in do_swap_page(), btw.)

For page caches, usually lock_page() cannot prevent accesses to them,
and there are several kernel functions which don't need PTE mappings
for access.  One of such functions is do_generic_mapping_read().

--
IWAMOTO Toshihiro
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