Re: [PATCH v3 0/3] idle memory tracking

[Minchan Kim <minchan@kernel.org>]

Hello Vladimir,

On Tue, Apr 28, 2015 at 03:24:39PM +0300, Vladimir Davydov wrote:
> Hi,
> 
> This patch set introduces a new user API for tracking user memory pages
> that have not been used for a given period of time. The purpose of this
> is to provide the userspace with the means of tracking a workload's
> working set, i.e. the set of pages that are actively used by the
> workload. Knowing the working set size can be useful for partitioning
> the system more efficiently, e.g. by tuning memory cgroup limits
> appropriately, or for job placement within a compute cluster.
> 
> ---- USE CASES ----
> 
> The unified cgroup hierarchy has memory.low and memory.high knobs, which
> are defined as the low and high boundaries for the workload working set
> size. However, the working set size of a workload may be unknown or
> change in time. With this patch set, one can periodically estimate the
> amount of memory unused by each cgroup and tune their memory.low and
> memory.high parameters accordingly, therefore optimizing the overall
> memory utilization.
> 
> Another use case is balancing workloads within a compute cluster.
> Knowing how much memory is not really used by a workload unit may help
> take a more optimal decision when considering migrating the unit to
> another node within the cluster.
> 
> ---- USER API ----
> 
> The user API consists of two new proc files:
> 
>  * /proc/kpageidle.  For each page this file contains a 64-bit number, which
>    equals 1 if the page is idle or 0 otherwise, indexed by PFN. A page is

Why do we need 64bit per page to indicate just idle or not?
What do you imagine we're happy with other 63bit in future?

-- 
Kind regards,
Minchan Kim

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