I think the answer is no answer.
On 10/11/07, shyam Burkule <shyam.burkule@xxxxxxxxx> wrote:
>
>
> The problem is how and when kernel (or may be processor) update the
> PG_referenced bti associated with page structure.
Ok, the following is extracted from Linux Kernel 3rd edition:
The PFRA collects the pages that were recently accessed in the active
list so that it will not scan them when looking for a page frame to
reclaim. Conversely, the PFRA collects the pages that have not been
accessed for a long time in the inactive list. Of course, pages should
move from the inactive list to the active list and back, according to
whether they are being accessed.
Clearly, two page states ("active" and "inactive") are not sufficient
to describe all possible access patterns. For instance, suppose a
logger process writes some data in a page once every hour. Although
the page is "inactive" for most of the time, the access makes it
"active," thus denying the reclaiming of the corresponding page frame,
even if it is not going to be accessed for an entire hour. Of course,
there is no general solution to this problem, because the PFRA has no
way to predict the behavior of User Mode processes; however, it seems
reasonable that pages should not change their status on every single
access.
The PG_referenced flag in the page descriptor is used to double the
number of accesses required to move a page from the inactive list to
the active list; it is also used to double the number of "missing
accesses" required to move a page from the active list to the inactive
list (see below). For instance, suppose that a page in the inactive
list has the PG_referenced flag set to 0. The first page access sets
the value of the flag to 1, but the page remains in the inactive list.
The second page access finds the flag set and causes the page to be
moved in the active list. If, however, the second access does not
occur within a given time interval after the first one, the page frame
reclaiming algorithm may reset the PG_referenced flag.
Ok, in the 2nd paragraph, there is a mention of one hour. Is this the answer?
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