[lkml]   [2013]   [Jan]   [8]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [RFC]x86: clearing access bit don't flush tlb
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.

All rights reversed

 \ /
  Last update: 2013-01-08 07:01    [W:0.055 / U:0.924 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site