On 01/08/2013 12:03 AM, H. Peter Anvin wrote:
On 01/07/2013 08:55 PM, Shaohua Li wrote:
I searched a little bit, the change (doing TLB flush to clear access bit) is
made between 2.6.7 - 2.6.8, I can't find the changelog, but I found a patch:
http://www.kernel.org/pub/linux/kernel/people/akpm/patches/2.6/2.6.7-rc2/2.6.7-rc2-mm2/broken-out/mm-flush-tlb-when-clearing-young.patch
The changelog declaims this is for arm/ppc/ppc64.
Not really. It says that those have stumbled over it already. It is
true in general that this change will make very frequently used pages
(which stick in the TLB) candidates for eviction.
That is only true if the pages were to stay in the TLB for a
very very long time. Probably multiple seconds.
x86 would seem to be just as affected, although possibly with a
different frequency.
Do we have any actual metrics on anything here?
I suspect that if we do need to force a TLB flush for page
reclaim purposes, it may make sense to do that TLB flush
asynchronously. For example, kswapd could kick off a TLB
flush of every CPU in the system once a second, when the
system is under pageout pressure.
We would have to do this in a smart way, so the kswapds
from multiple nodes do not duplicate the work.
If people want that kind of functionality, I would be
happy to cook up an RFC patch.
--
All rights reversed
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxx. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>