On Tue, Jul 21, 2015 at 04:35:00PM -0700, Andrew Morton wrote:

On Sun, 19 Jul 2015 15:31:16 +0300 Vladimir Davydov [off-list ref] wrote:

quoted

As noted by Minchan, a benefit of reading idle flag from
/proc/kpageflags is that one can easily filter dirty and/or unevictable
pages while estimating the size of unused memory.

Note that idle flag read from /proc/kpageflags may be stale in case the
page was accessed via a PTE, because it would be too costly to iterate
over all page mappings on each /proc/kpageflags read to provide an
up-to-date value. To make sure the flag is up-to-date one has to read
/proc/kpageidle first.

Is there any value in teaching the regular old page scanner to update
these flags?  If it's doing an rmap scan anyway...

I don't understand what you mean by "regular old page scanner". Could
you please elaborate?

Thanks,
Vladimir