Re: Page aging broken in 2.6

[Roger Luethi <rl@hellgate.ch>]

On Fri, 26 Dec 2003 19:00:45 -0800, Andrew Morton wrote:
> The current behaviour seems better from a theoretical point of view.  All
> we want to know is the reference pattern - whether it is one process
> referencing the page frequently or 100 processes referencing it
> infrequently shouldn't matter.  And if we want to give mapped pages more

It can matter. Evicting a page that is infrequently referenced by many
processes increases the chance that all runnable processes block waiting
for that same page later. The likelihood of that happening grows under
memory pressure, when "infrequently" may actually be "quite often" and
when disk I/O is congested (resulting in higher disk access times).

You won't have the same effect when evicting a page that is referenced
by one process only, no matter how frequently.

Having all processes blocked is indeed one problem of 2.6 under memory
pressure. I don't know what the cause is, though.

Roger