Messages in this thread | | | Date | Wed, 11 Apr 2012 13:17:02 -0400 | From | Rik van Riel <> | Subject | Re: [PATCH 0/3] Removal of lumpy reclaim V2 |
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On 04/11/2012 12:38 PM, Mel Gorman wrote:
> Success rates are completely hosed for 3.4-rc2 which is almost certainly > due to [fe2c2a10: vmscan: reclaim at order 0 when compaction is enabled]. I > expected this would happen for kswapd and impair allocation success rates > (https://lkml.org/lkml/2012/1/25/166) but I did not anticipate this much > a difference: 80% less scanning, 37% less reclaim by kswapd
Also, no gratuitous pageouts of anonymous memory. That was what really made a difference on a somewhat heavily loaded desktop + kvm workload.
> In comparison, reclaim/compaction is not aggressive and gives up easily > which is the intended behaviour. hugetlbfs uses __GFP_REPEAT and would be > much more aggressive about reclaim/compaction than THP allocations are. The > stress test above is allocating like neither THP or hugetlbfs but is much > closer to THP.
Next step: get rid of __GFP_NO_KSWAPD for THP, first in the -mm kernel
> Mainline is now impaired in terms of high order allocation under heavy load > although I do not know to what degree as I did not test with __GFP_REPEAT. > Keep this in mind for bugs related to hugepage pool resizing, THP allocation > and high order atomic allocation failures from network devices.
This might be due to smaller allocations not bumping the compaction deferring code, when we have deferred compaction for a higher order allocation.
I wonder if the compaction deferring code is simply too defer-happy, now that we ignore compaction at lower orders than where compaction failed?
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