From 3fb2a585729a37e205c5ea42ac6c48d4a6c0a29c Mon Sep 17 00:00:00 2001
From: KOSAKI Motohiro<kosaki.motohiro@xxxxxxxxxxxxxx>
Date: Fri, 4 Dec 2009 12:54:37 +0900
Subject: [PATCH 6/7] wipe_page_reference return SWAP_AGAIN if VM pressulre is low and lock contention is detected.
Larry Woodman reported AIM7 makes serious ptelock and anon_vma_lock
contention on current VM. because SplitLRU VM (since 2.6.28) remove
calc_reclaim_mapped() test, then shrink_active_list() always call
page_referenced() against mapped page although VM pressure is low.
Lightweight VM pressure is very common situation and it easily makes
ptelock contention with page fault. then, anon_vma_lock is holding
long time and it makes another lock contention. then, fork/exit
throughput decrease a lot.