lkml.org 
[lkml]   [2010]   [Dec]   [9]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    Date
    From
    SubjectRe: [PATCH 2/6] mm: kswapd: Keep kswapd awake for high-order allocations until a percentage of the node is balanced
    On Thu,  9 Dec 2010 11:18:16 +0000
    Mel Gorman <mel@csn.ul.ie> wrote:

    > When reclaiming for high-orders, kswapd is responsible for balancing a
    > node but it should not reclaim excessively. It avoids excessive reclaim by
    > considering if any zone in a node is balanced then the node is balanced. In
    > the cases where there are imbalanced zone sizes (e.g. ZONE_DMA with both
    > ZONE_DMA32 and ZONE_NORMAL), kswapd can go to sleep prematurely as just
    > one small zone was balanced.
    >
    > This alters the sleep logic of kswapd slightly. It counts the number of pages
    > that make up the balanced zones. If the total number of balanced pages is
    > more than a quarter of the zone, kswapd will go back to sleep. This should
    > keep a node balanced without reclaiming an excessive number of pages.
    >
    > Signed-off-by: Mel Gorman <mel@csn.ul.ie>

    Hmm, does this work well in

    for example, x86-32,
    DMA: 16MB
    NORMAL: 700MB
    HIGHMEM: 11G
    ?

    At 1st look, it's balanced when HIGHMEM has enough free pages...
    This is not good for NICs which requests high-order allocations.

    Can't we take claszone_idx into account at checking rather than
    node->present_pages ?

    as
    balanced > present_pages_below_classzone_idx(node, classzone_idx)/4

    ?
    Thanks,
    -Kame

    > ---
    > mm/vmscan.c | 43 ++++++++++++++++++++++++++++++++++---------
    > 1 files changed, 34 insertions(+), 9 deletions(-)
    >
    > diff --git a/mm/vmscan.c b/mm/vmscan.c
    > index 25cb373..b4472a1 100644
    > --- a/mm/vmscan.c
    > +++ b/mm/vmscan.c
    > @@ -2117,10 +2117,26 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *mem_cont,
    > }
    > #endif
    >
    > +/*
    > + * pgdat_balanced is used when checking if a node is balanced for high-order
    > + * allocations. Only zones that meet watermarks make up "balanced".
    > + * The total of balanced pages must be at least 25% of the node for the
    > + * node to be considered balanced. Forcing all zones to be balanced for high
    > + * orders can cause excessive reclaim when there are imbalanced zones.
    > + * Similarly, we do not want kswapd to go to sleep because ZONE_DMA happens
    > + * to be balanced when ZONE_DMA32 is huge in comparison and unbalanced
    > + */
    > +static bool pgdat_balanced(pg_data_t *pgdat, unsigned long balanced)
    > +{
    > + return balanced > pgdat->node_present_pages / 4;
    > +}
    > +
    > /* is kswapd sleeping prematurely? */
    > static int sleeping_prematurely(pg_data_t *pgdat, int order, long remaining)
    > {
    > int i;
    > + unsigned long balanced = 0;
    > + bool all_zones_ok = true;
    >
    > /* If a direct reclaimer woke kswapd within HZ/10, it's premature */
    > if (remaining)
    > @@ -2138,10 +2154,19 @@ static int sleeping_prematurely(pg_data_t *pgdat, int order, long remaining)
    >
    > if (!zone_watermark_ok(zone, order, high_wmark_pages(zone),
    > 0, 0))
    > - return 1;
    > + all_zones_ok = false;
    > + else
    > + balanced += zone->present_pages;
    > }
    >
    > - return 0;
    > + /*
    > + * For high-order requests, any zone meeting the watermark allows
    > + * kswapd to sleep. For order-0, all zones must be balanced
    > + */
    > + if (order)
    > + return pgdat_balanced(pgdat, balanced);
    > + else
    > + return !all_zones_ok;
    > }
    >
    > /*
    > @@ -2169,7 +2194,7 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
    > int classzone_idx)
    > {
    > int all_zones_ok;
    > - int any_zone_ok;
    > + unsigned long balanced;
    > int priority;
    > int i;
    > int end_zone = 0; /* Inclusive. 0 = ZONE_DMA */
    > @@ -2203,7 +2228,7 @@ loop_again:
    > disable_swap_token();
    >
    > all_zones_ok = 1;
    > - any_zone_ok = 0;
    > + balanced = 0;
    >
    > /*
    > * Scan in the highmem->dma direction for the highest
    > @@ -2314,11 +2339,11 @@ loop_again:
    > */
    > zone_clear_flag(zone, ZONE_CONGESTED);
    > if (i <= classzone_idx)
    > - any_zone_ok = 1;
    > + balanced += zone->present_pages;
    > }
    >
    > }
    > - if (all_zones_ok || (order && any_zone_ok))
    > + if (all_zones_ok || (order && pgdat_balanced(pgdat, balanced)))
    > break; /* kswapd: all done */
    > /*
    > * OK, kswapd is getting into trouble. Take a nap, then take
    > @@ -2344,10 +2369,10 @@ out:
    >
    > /*
    > * order-0: All zones must meet high watermark for a balanced node
    > - * high-order: Any zone below pgdats classzone_idx must meet the high
    > - * watermark for a balanced node
    > + * high-order: Balanced zones must make up at least 25% of the node
    > + * for the node to be balanced
    > */
    > - if (!(all_zones_ok || (order && any_zone_ok))) {
    > + if (!(all_zones_ok || (order && pgdat_balanced(pgdat, balanced)))) {
    > cond_resched();
    >
    > try_to_freeze();
    > --
    > 1.7.1
    >
    > --
    > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    > the body of a message to majordomo@vger.kernel.org
    > More majordomo info at http://vger.kernel.org/majordomo-info.html
    > Please read the FAQ at http://www.tux.org/lkml/
    >



    \
     
     \ /
      Last update: 2010-12-10 02:25    [W:0.036 / U:0.088 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site