• Minchan Kim's avatar
    mm: vmscan: correctly check if reclaimer should schedule during shrink_slab · f06590bd
    Minchan Kim authored
    It has been reported on some laptops that kswapd is consuming large
    amounts of CPU and not being scheduled when SLUB is enabled during large
    amounts of file copying.  It is expected that this is due to kswapd
    missing every cond_resched() point because;
    
    shrink_page_list() calls cond_resched() if inactive pages were isolated
            which in turn may not happen if all_unreclaimable is set in
            shrink_zones(). If for whatver reason, all_unreclaimable is
            set on all zones, we can miss calling cond_resched().
    
    balance_pgdat() only calls cond_resched if the zones are not
            balanced. For a high-order allocation that is balanced, it
            checks order-0 again. During that window, order-0 might have
            become unbalanced so it loops again for order-0 and returns
            that it was reclaiming for order-0 to kswapd(). It can then
            find that a caller has rewoken kswapd for a high-order and
            re-enters balance_pgdat() without ever calling cond_resched().
    
    shrink_slab only calls cond_resched() if we are reclaiming slab
    	pages. If there are a large number of direct reclaimers, the
    	shrinker_rwsem can be contended and prevent kswapd calling
    	cond_resched().
    
    This patch modifies the shrink_slab() case.  If the semaphore is
    contended, the caller will still check cond_resched().  After each
    successful call into a shrinker, the check for cond_resched() remains in
    case one shrinker is particularly slow.
    
    [mgorman@suse.de: preserve call to cond_resched after each call into shrinker]
    Signed-off-by: default avatarMel Gorman <mgorman@suse.de>
    Signed-off-by: default avatarMinchan Kim <minchan.kim@gmail.com>
    Cc: Rik van Riel <riel@redhat.com>
    Cc: Johannes Weiner <hannes@cmpxchg.org>
    Cc: Wu Fengguang <fengguang.wu@intel.com>
    Cc: James Bottomley <James.Bottomley@HansenPartnership.com>
    Tested-by: default avatarColin King <colin.king@canonical.com>
    Cc: Raghavendra D Prabhu <raghu.prabhu13@gmail.com>
    Cc: Jan Kara <jack@suse.cz>
    Cc: Chris Mason <chris.mason@oracle.com>
    Cc: Christoph Lameter <cl@linux.com>
    Cc: Pekka Enberg <penberg@kernel.org>
    Cc: Rik van Riel <riel@redhat.com>
    Cc: <stable@kernel.org>		[2.6.38+]
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    f06590bd
vmscan.c 92.5 KB