Re: [PATCH -mm] mm: have order>0 compaction start off where it left
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On 06/28/2012 01:16 PM, Jim Schutt wrote:
On 06/27/2012 09:37 PM, Rik van Riel wrote:Order> 0 compaction stops when enough free pages of the correct page order have been coalesced. When doing subsequent higher order allocations, it is possible for compaction to be invoked many times. However, the compaction code always starts out looking for things to compact at the start of the zone, and for free pages to compact things to at the end of the zone. This can cause quadratic behaviour, with isolate_freepages starting at the end of the zone each time, even though previous invocations of the compaction code already filled up all free memory on that end of the zone. This can cause isolate_freepages to take enormous amounts of CPU with certain workloads on larger memory systems. The obvious solution is to have isolate_freepages remember where it left off last time, and continue at that point the next time it gets invoked for an order> 0 compaction. This could cause compaction to fail if cc->free_pfn and cc->migrate_pfn are close together initially, in that case we restart from the end of the zone and try once more. Forced full (order == -1) compactions are left alone. Reported-by: Jim Schutt<jaschut@xxxxxxxxxx> Signed-off-by: Rik van Riel<riel@xxxxxxxxxx>Tested-by: Jim Schutt<jaschut@xxxxxxxxxx> Please let me know if you further refine this patch and would like me to test it with my workload.
Mel pointed out a serious problem with the way wrapping cc->free_pfn back to the top of the zone is handled. I will send you a new patch once I have a fix for that.
So far I've run a total of ~20 TB of data over fifty minutes or so through 12 machines running this patch; no hint of trouble, great performance. Without this patch I would typically start having trouble after just a few minutes of this load.
Good to hear that! Thank you for testing last night's version. -- All rights reversed -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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