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authorAlex Shi <alex.shi@intel.com>2011-10-31 17:08:45 -0700
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2012-08-01 12:27:17 -0700
commit9203b3fa57cc16bf1ad1be7c64b01b5e45cc6151 (patch)
treef8a847fbadb5cfc577024f5634d5943a7af2bfa2 /mm/compaction.c
parent5d62e5ca429b85ecadaa5042bdb1d8b88d4bfe80 (diff)
downloadlwn-9203b3fa57cc16bf1ad1be7c64b01b5e45cc6151.tar.gz
lwn-9203b3fa57cc16bf1ad1be7c64b01b5e45cc6151.zip
kswapd: assign new_order and new_classzone_idx after wakeup in sleeping
commit f0dfcde099453aa4c0dc42473828d15a6d492936 upstream. Stable note: Fixes https://bugzilla.redhat.com/show_bug.cgi?id=712019. This patch reduces kswapd CPU usage. There 2 places to read pgdat in kswapd. One is return from a successful balance, another is waked up from kswapd sleeping. The new_order and new_classzone_idx represent the balance input order and classzone_idx. But current new_order and new_classzone_idx are not assigned after kswapd_try_to_sleep(), that will cause a bug in the following scenario. 1: after a successful balance, kswapd goes to sleep, and new_order = 0; new_classzone_idx = __MAX_NR_ZONES - 1; 2: kswapd waked up with order = 3 and classzone_idx = ZONE_NORMAL 3: in the balance_pgdat() running, a new balance wakeup happened with order = 5, and classzone_idx = ZONE_NORMAL 4: the first wakeup(order = 3) finished successufly, return order = 3 but, the new_order is still 0, so, this balancing will be treated as a failed balance. And then the second tighter balancing will be missed. So, to avoid the above problem, the new_order and new_classzone_idx need to be assigned for later successful comparison. Signed-off-by: Alex Shi <alex.shi@intel.com> Acked-by: Mel Gorman <mgorman@suse.de> Reviewed-by: Minchan Kim <minchan.kim@gmail.com> Tested-by: Pádraig Brady <P@draigBrady.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Mel Gorman <mgorman@suse.de> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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