Messages in this thread | | | Date | Mon, 16 Jul 2007 11:37:04 +0100 | Subject | Re: -mm merge plans -- lumpy reclaim | From | (Mel Gorman) |
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On (11/07/07 09:46), Andrew Morton didst pronounce: > On Wed, 11 Jul 2007 10:34:31 +0100 Andy Whitcroft <apw@shadowen.org> wrote: > > > [Seems a PEBKAC occured on the subject line, resending lest it become a > > victim of "oh thats spam".] > > > > Andy Whitcroft wrote: > > > Andrew Morton wrote: > > > > > > [...] > > >> lumpy-reclaim-v4.patch > > >> have-kswapd-keep-a-minimum-order-free-other-than-order-0.patch > > >> only-check-absolute-watermarks-for-alloc_high-and-alloc_harder-allocations.patch > > >> > > >> Lumpy reclaim. In a similar situation to Mel's patches. Stuck due to > > >> general lack or interest and effort. > > > > > > The lumpy reclaim patches originally came out of work to support Mel's > > > anti-fragmentation work. As such I think they have become somewhat > > > attached to those patches. Whilst lumpy is most effective where > > > placement controls are in place as offered by Mel's work, we see benefit > > > from reduction in the "blunderbuss" effect when we reclaim at higher > > > orders. While placement control is pretty much required for the very > > > highest orders such as huge page size, lower order allocations are > > > benefited in terms of lower collateral damage. > > > > > > There are now a few areas other than huge page allocations which can > > > benefit. Stacks are still order 1. Jumbo frames want higher order > > > contiguous pages for there incoming hardware buffers. SLUB is showing > > > performance benefits from moving to a higher allocation order. All of > > > these should benefit from more aggressive targeted reclaim, indeed I > > > have been surprised just how often my test workloads trigger lumpy at > > > order 1 to get new stacks. > > > > > > Truly representative work loads are hard to generate for some of these. > > > Though we have heard some encouraging noises from those who can > > > reproduce these problems. > > I'd expect that the main application for lumpy-reclaim is in keeping a pool > of order-2 (say) pages in reserve for GFP_ATOMIC allocators. ie: jumbo > frames. > > At present this relies upon the wakeup_kswapd(..., order) mechanism. > > How effective is this at solving the jumbo frame problem? > > (And do we still have a jumbo frame problem? Reports seems to have subsided)
The patches have an application with hugepage pool resizing.
When lumpy-reclaim is used used with ZONE_MOVABLE, the hugepages pool can be resized with greater reliability. Testing on a desktop machine with 2GB of RAM showed that growing the hugepage pool with ZONE_MOVABLE on it's own was very slow as the success rate was quite low. Without lumpy-reclaim, each attempt to grow the pool by 100 pages would yield 1 or 2 hugepages. With lumpy-reclaim, getting 40 to 70 hugepages on each attempt was typical.
-- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org 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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