On Wed, 22 Jul 2015 19:25:28 +0300 Vladimir Davydov [off-list ref] wrote:

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

quoted

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?

Whenever kswapd or direct reclaim perform an rmap scan, take that as an
opportunity to also update PageIdle().