• Mel Gorman's avatar
    vmscan: count the number of times zone_reclaim() scans and fails · 24cf7251
    Mel Gorman authored
    On NUMA machines, the administrator can configure zone_reclaim_mode that
    is a more targetted form of direct reclaim.  On machines with large NUMA
    distances for example, a zone_reclaim_mode defaults to 1 meaning that
    clean unmapped pages will be reclaimed if the zone watermarks are not
    being met.
    
    There is a heuristic that determines if the scan is worthwhile but it is
    possible that the heuristic will fail and the CPU gets tied up scanning
    uselessly.  Detecting the situation requires some guesswork and
    experimentation so this patch adds a counter "zreclaim_failed" to
    /proc/vmstat.  If during high CPU utilisation this counter is increasing
    rapidly, then the resolution to the problem may be to set
    /proc/sys/vm/zone_reclaim_mode to 0.
    
    [akpm@linux-foundation.org: name things consistently]
    Signed-off-by: default avatarMel Gorman <mel@csn.ul.ie>
    Reviewed-by: default avatarRik van Riel <riel@redhat.com>
    Cc: Christoph Lameter <cl@linux-foundation.org>
    Reviewed-by: default avatarKOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
    Cc: Wu Fengguang <fengguang.wu@intel.com>
    Cc: <stable@kernel.org>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    24cf7251
vmstat.c 22 KB