On 10/21/2013 05:26 AM, Vlastimil Babka wrote:
On 10/10/2013 11:46 PM, Johannes Weiner wrote:
Hi everyone,
here is an update to the cache sizing patches for 3.13.
Changes in this revision
o Drop frequency synchronization between refaulted and demoted pages
and just straight up activate refaulting pages whose access
frequency indicates they could stay in memory. This was suggested
by Rik van Riel a looong time ago but misinterpretation of test
results during early stages of development took me a while to
overcome. It's still the same overall concept, but a little simpler
and with even faster cache adaptation. Yay!
Oh, I liked the previous approach with direct competition between the
refaulted and demoted page :) Doesn't the new approach favor the
refaulted page too much? No wonder it leads to faster cache adaptation,
but could it also cause degradations for workloads that don't benefit
from it? Were there any tests for performance regressions on workloads
that were not the target of the patchset?
This is a good question, and one that is probably
best settled through experimentation.
Even with the first scheme (fault refaulted page to
the inactive list), those pages only need 2 accesses
to be promoted to the active list.
That is because a refault tends to immediately be
followed by an access (after all, the attempted
access causes the page to get loaded back into memory).
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