On Wed, Dec 10, 2014 at 04:06:19PM +0100, Vlastimil Babka wrote: > On 12/05/2014 02:07 AM, Joonsoo Kim wrote: > >------------>8----------------- > > From b7daa232c327a4ebbb48ca0538a2dbf9ca83ca1f Mon Sep 17 00:00:00 2001 > >From: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> > >Date: Fri, 5 Dec 2014 09:38:30 +0900 > >Subject: [PATCH] mm/compaction: stop the compaction if there isn't enough > > freepage > > > >After compaction_suitable() passed, there is no check whether the system > >has enough memory to compact and blindly try to find freepage through > >iterating all memory range. This causes excessive cpu usage in low free > >memory condition and finally compaction would be failed. It makes sense > >that compaction would be stopped if there isn't enough freepage. So, > >this patch adds watermark check to isolate_freepages() in order to stop > >the compaction in this case. > > > >Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> > >--- > > mm/compaction.c | 9 +++++++++ > > 1 file changed, 9 insertions(+) > > > >diff --git a/mm/compaction.c b/mm/compaction.c > >index e005620..31c4009 100644 > >--- a/mm/compaction.c > >+++ b/mm/compaction.c > >@@ -828,6 +828,7 @@ static void isolate_freepages(struct compact_control *cc) > > unsigned long low_pfn; /* lowest pfn scanner is able to scan */ > > int nr_freepages = cc->nr_freepages; > > struct list_head *freelist = &cc->freepages; > >+ unsigned long watermark = low_wmark_pages(zone) + (2UL << cc->order); > > Given that we maybe have already isolated up to 31 free pages (if > cc->nr_migratepages is the maximum 32), then this is somewhat > stricter than the check in isolation_suitable() (when nothing was > isolated yet) and may interrupt us prematurely. We should allow for > some slack. Okay. Will allow some slack. > > > > > /* > > * Initialise the free scanner. The starting point is where we last > >@@ -903,6 +904,14 @@ static void isolate_freepages(struct compact_control *cc) > > */ > > if (cc->contended) > > break; > >+ > >+ /* > >+ * Watermarks for order-0 must be met for compaction. > >+ * See compaction_suitable for more detailed explanation. > >+ */ > >+ if (!zone_watermark_ok(zone, 0, watermark, > >+ cc->classzone_idx, cc->alloc_flags)) > >+ break; > > } > > I'm a also bit concerned about the overhead of doing this in each pageblock. Yep, we can do it whenever SWAP_CLUSTER_MAX pageblock is scanned. It will reduce overhead somewhat. I will change it. > > I wonder if there could be a mechanism where a process entering > reclaim or compaction with the goal of meeting the watermarks to > allocate, should increase the watermarks needed for further parallel > allocation attempts to pass. Then it shouldn't happen that somebody > else steals the memory. I don't know, neither. Thanks. > > > /* split_free_page does not map the pages */ > > > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@xxxxxxxxx. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a> -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>