Re: question about try_to_swap_out()

["Stephen C. Tweedie" <sct@redhat.com>]

Hi,

On Sun, 10 Jan 1999 21:38:46 -0600, "Paul R. Wilson"
<wilson@cs.utexas.edu> said:

> After checking that that a page is present and pageable, try_to_swap_out()
> checks to see if the page is reserved or locked or not DMA'able when
> where looking for a DMA page.  If any of these three things is
> true, it returns 0 without changing anything.

> It seems to me that it should go ahead and check the pte age bit,
> and update the page frame's PG_referenced bit, before returning 0.

Not really.  Reserved pages never get swapped anyway.  For DMA, we don't
want to disturb non-DMA processes at all --- the demand for DMA and
non-DMA pages might be very different.  For locked pages, we expect this
to be sufficiently rare that it's totally irrelevant whether we age the
page or not.

> Am I off-base here, or should the conditional that checks to see
> whether a page is young (and updates the reference bits) be moved
> up ahead of the conditional that checks to see whether a page
> is (reserved | locked | not-dma-but-we-need-dma)?

I really don't think it's that important!

--Stephen
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