Messages in this thread | | | Date | Fri, 23 Nov 2012 16:50:26 +0800 | From | Jaegeuk Hanse <> | Subject | Re: kswapd endless loop for compaction |
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On 11/21/2012 03:04 AM, Johannes Weiner wrote: > Hi guys, > > while testing a 3.7-rc5ish kernel, I noticed that kswapd can drop into > a busy spin state without doing reclaim. printk-style debugging told > me that this happens when the distance between a zone's high watermark > and its low watermark is less than two huge pages (DMA zone). > > 1. The first loop in balance_pgdat() over the zones finds all zones to > be above their high watermark and only does goto out (all_zones_ok). > > 2. pgdat_balanced() at the out: label also just checks the high > watermark, so the node is considered balanced and the order is not > reduced. > > 3. In the `if (order)' block after it, compaction_suitable() checks if > the zone's low watermark + twice the huge page size is okay, which > it's not necessarily in a small zone, and so COMPACT_SKIPPED makes it > it go back to loop_again:. > > This will go on until somebody else allocates and breaches the high > watermark and then hopefully goes on to reclaim the zone above low > watermark + 2 * THP. > > I'm not really sure what the correct solution is. Should we modify > the zone_watermark_ok() checks in balance_pgdat() to take into account > the higher watermark requirements for reclaim on behalf of compaction? > Change the check in compaction_suitable() / not use it directly?
Hi Johannes,
If depend on compaction get enough contigous pages, why
if (CONPACT_BUILD && order && compaction_suitable(zone, order) != COMPACTION_SKIPPED) testorder = 0;
can't guarantee low watermark + twice the huge page size is okay?
Regards, Jaegeuk
> Thanks, > Johannes > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@kvack.org. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
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