• David Rientjes's avatar
    mm: fix deferred congestion timeout if preferred zone is not allowed · f33261d7
    David Rientjes authored
    Before 0e093d99 ("writeback: do not sleep on the congestion queue if
    there are no congested BDIs or if significant congestion is not being
    encountered in the current zone"), preferred_zone was only used for NUMA
    statistics, to determine the zoneidx from which to allocate from given
    the type requested, and whether to utilize memory compaction.
    
    wait_iff_congested(), though, uses preferred_zone to determine if the
    congestion wait should be deferred because its dirty pages are backed by
    a congested bdi.  This incorrectly defers the timeout and busy loops in
    the page allocator with various cond_resched() calls if preferred_zone
    is not allowed in the current context, usually consuming 100% of a cpu.
    
    This patch ensures preferred_zone is an allowed zone in the fastpath
    depending on whether current is constrained by its cpuset or nodes in
    its mempolicy (when the nodemask passed is non-NULL).  This is correct
    since the fastpath allocation always passes ALLOC_CPUSET when trying to
    allocate memory.  In the slowpath, this patch resets preferred_zone to
    the first zone of the allowed type when the allocation is not
    constrained by current's cpuset, i.e.  it does not pass ALLOC_CPUSET.
    
    This patch also ensures preferred_zone is from the set of allowed nodes
    when called from within direct reclaim since allocations are always
    constrained by cpusets in this context (it is blockable).
    
    Both of these uses of cpuset_current_mems_allowed are protected by
    get_mems_allowed().
    Signed-off-by: default avatarDavid Rientjes <rientjes@google.com>
    Cc: Mel Gorman <mel@csn.ul.ie>
    Cc: Johannes Weiner <hannes@cmpxchg.org>
    Cc: Minchan Kim <minchan.kim@gmail.com>
    Cc: Wu Fengguang <fengguang.wu@intel.com>
    Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
    Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
    Acked-by: default avatarRik van Riel <riel@redhat.com>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    f33261d7
vmscan.c 92.1 KB