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SubjectRe: [RFC]x86: clearing access bit don't flush tlb
On 01/07/2013 09:08 PM, Rik van Riel wrote:
> 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:
>>> 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.

So it sounds like you're saying that this patch should never have been
applied in the first place?


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