Re: [PATCH 05/11] unpaged: VM_UNPAGED

From: William Lee Irwin III
Date: Thu Nov 17 2005 - 16:00:53 EST

On Thu, Nov 17, 2005 at 07:34:55PM +0000, Hugh Dickins wrote:
> Although we tend to associate VM_RESERVED with remap_pfn_range, quite a
> few drivers set VM_RESERVED on areas which are then populated by nopage.
> The PageReserved removal in 2.6.15-rc1 changed VM_RESERVED not to free
> pages in zap_pte_range, without changing those drivers not to set it:
> so their pages just leak away.
> Let's not change miscellaneous drivers now: introduce VM_UNPAGED at the
> core, to flag the special areas where the ptes may have no struct page,
> or if they have then it's not to be touched. Replace most instances of
> VM_RESERVED in core mm by VM_UNPAGED. Force it on in remap_pfn_range,
> and the sparc and sparc64 io_remap_pfn_range.
> Revert addition of VM_RESERVED to powerpc vdso, it's not needed there.
> Is it needed anywhere? It still governs the mm->reserved_vm statistic,
> and special vmas not to be merged, and areas not to be core dumped; but
> could probably be eliminated later (the drivers are probably specifying
> it because in 2.4 it kept swapout off the vma, but in 2.6 we work from
> the LRU, which these pages don't get on).

Eminently reasonable. This solves a lot of problems.
Acked-by: William Irwin <wli@xxxxxxxxxxxxxx>

-- wli
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