On Thu, 13 Jan 2000, Linus Torvalds wrote:

HOWEVER, I don't think this is going to be a huge issue in most cases. And
if people don't need non-DMA memory, then the pages we "swapped" out are
going to stay in RAM anyway, so it's not going to hurt us.

Anyway, I obviously do agree that I may well be wrong, and that real life
is going to come back and bite us, and we'll end up having to not do it
this way. However, I'd prefer trying the "conceptually simple" path first,
and only if it turns out that yes, I was completely wrong, do we try to
fix it up with magic heuristics etc.

hm., i think we'll see this with ISA soundcards (still the majority) if
used as modules. Right now kswapd just gives up too easy and says 'no such
page', on a box with lots of RAM and all DMA allocated in process VM
space.

Anyway, the patch and suggestion of passing in a single zone is i believe
completely wrong, because it advances mm->swap_address, which unfairly
selects a given range to be checked for only one zone. So i think it's
either zone-bitmaps (or equivalent multi-zone logic) or what you
suggested, to have no zone-awareness in swap_out() for now at all.

(i believe this is also going to bite us with the IA64 port - kswapd will
have no information to free pages from the right node, we could solve this
already with a zone bitmap, or by starting per-zone kswapds. The latter
one looks like overkill to me, but it's conceptually cleaner than bitmaps
and and does not have a limitation on the number of zones. Might not be a
highprio issue though.)

-- mingo

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