Messages in this thread | | | Date | Thu, 21 Mar 2013 08:30:41 -0400 | From | Rik van Riel <> | Subject | Re: [PATCH 05/10] mm: vmscan: Do not allow kswapd to scan at maximum priority |
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On 03/21/2013 06:12 AM, Mel Gorman wrote: > On Wed, Mar 20, 2013 at 09:20:14PM -0400, Rik van Riel wrote: >> On 03/17/2013 09:04 AM, Mel Gorman wrote: >>> Page reclaim at priority 0 will scan the entire LRU as priority 0 is >>> considered to be a near OOM condition. Kswapd can reach priority 0 quite >>> easily if it is encountering a large number of pages it cannot reclaim >>> such as pages under writeback. When this happens, kswapd reclaims very >>> aggressively even though there may be no real risk of allocation failure >>> or OOM. >>> >>> This patch prevents kswapd reaching priority 0 and trying to reclaim >>> the world. Direct reclaimers will still reach priority 0 in the event >>> of an OOM situation. >>> >>> Signed-off-by: Mel Gorman <mgorman@suse.de> >>> --- >>> mm/vmscan.c | 2 +- >>> 1 file changed, 1 insertion(+), 1 deletion(-) >>> >>> diff --git a/mm/vmscan.c b/mm/vmscan.c >>> index 7513bd1..af3bb6f 100644 >>> --- a/mm/vmscan.c >>> +++ b/mm/vmscan.c >>> @@ -2891,7 +2891,7 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order, >>> */ >>> if (raise_priority || !this_reclaimed) >>> sc.priority--; >>> - } while (sc.priority >= 0 && >>> + } while (sc.priority >= 1 && >>> !pgdat_balanced(pgdat, order, *classzone_idx)); >>> >>> out: >>> >> >> If priority 0 is way way way way way too aggressive, what makes >> priority 1 safe? >> > > The fact that priority 1 selects a sensible number of pages to reclaim and > obeys swappiness makes it a lot safer. Priority 0 does this in get_scan_count ^^^^^^^^^^^^^^^^
Ahhh, good point! We stay away from all the "emergency" code, which kswapd should never run.
Acked-by: Rik van Riel <riel@redhat.com>
-- All rights reversed
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