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Page migration

Page migration

Posted Oct 27, 2005 22:31 UTC (Thu) by Duncan (guest, #6647)
Parent article: Page migration

> Migrating pages by way of the swap device
> is not the most efficient way of moving
> them across a NUMA system.

... Especially for those of us that have swap disabled! It'll be nice to
have migration working, but what's this with forcing it out to slow swap
so it can be faulted back in on the other node? It's likely that's so
slow the cost of doing it exceeds the potential benefit of NUMA optimized
memory accesses for the remaining lifetime of the process, in many cases!

Of course, if by "swapped out" and "faulted back in", it just means a trip
out of directly allocated memory into cache memory and faulted back in
from there, no big deal (unless no swap mean's it's disabled), but if it's
actually written to disk, that's /quite/ a bit of extra latency to make up
in NUMA optimization, enough so it's not likely to be worth it save for
processes running (and accessing that memory) for > an hour, anyway.

So... I guess my view on this depends on the defined value of
"eventually", altho I think I'd still prefer it wait out a version, to be
merged with .16 (or later), if it's all going to be swap dependant
for .15. After all, it's not like the patches won't still be there for
those that want them with .15, anyway, just not mainlined (-mm might be


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