Re: [patch 1/1] vmscan: give referenced, active and unmapped pages a second trip around the LRU

[Rik van Riel <riel@redhat.com>]

Peter Zijlstra wrote:

> -		if (page_mapped(page)) {
> -			if (!reclaim_mapped ||
> -			    (total_swap_pages == 0 && PageAnon(page)) ||
> -			    page_referenced(page, 0)) {
> -				list_add(&page->lru, &l_active);
> -				continue;

This code is problematic, too.  We essentially randomize the
LRU order of the mapped pages while !reclaim_mapped, while
clearing the referenced bits on those pages.

By the time we start swapping out mapped pages, the list has
been randomized and replacement starts getting pretty bad.


Of course, these problems are pretty small compared to how
my 2GB test system misbehaves when running AIM7.

When the system runs out of memory, everything starts swapping
all at once.  Unfortunately vmstat got stuck too, so I could
not observe the start of swapping.  Once the system had freed
up 900MB (of 2GB total RAM!), vmstat returned.  The system did
not stop swapping until 1.4GB of memory was free!

With the system behaving this badly at a macro level, I do
not think page reclaim tweaks can be usefully tested...

-- 
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