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Message-Id: <1235639427.11390.11.camel@minggr> Date: Thu, 26 Feb 2009 17:10:27 +0800 From: Lin Ming <ming.m.lin@...el.com> To: Mel Gorman <mel@....ul.ie> Cc: Linux Memory Management List <linux-mm@...ck.org>, Pekka Enberg <penberg@...helsinki.fi>, Rik van Riel <riel@...hat.com>, KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>, Christoph Lameter <cl@...ux-foundation.org>, Johannes Weiner <hannes@...xchg.org>, Nick Piggin <npiggin@...e.de>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, Zhang Yanmin <yanmin_zhang@...ux.intel.com>, Peter Zijlstra <peterz@...radead.org> Subject: Re: [RFC PATCH 00/19] Cleanup and optimise the page allocator V2 We tested this v2 patch series with 2.6.29-rc6 on different machines. 4P qual-core 2P qual-core 2P qual-core HT tigerton stockley Nehalem ------------------------------------------------ tbench +3% +2% 0% oltp -2% 0% 0% aim7 0% 0% 0% specjbb2005 +3% 0% 0% hackbench 0% 0% 0% netperf: TCP-S-112k 0% -1% 0% TCP-S-64k 0% -1% +1% TCP-RR-1 0% 0% +1% UDP-U-4k -2% 0% -2% UDP-U-1k +3% 0% 0% UDP-RR-1 0% 0% 0% UDP-RR-512 -1% 0% +1% Lin Ming On Tue, 2009-02-24 at 20:16 +0800, Mel Gorman wrote: > Still a work in progress but enough has changed that I want to show what > it current looks like. Performance is still improved a little but there are > some large outstanding pieces of fruit > > 1. Improving free_pcppages_bulk() does a lot of looping, maybe could be better > 2. gfp_zone() is still using a cache line for data. I wasn't able to translate > Kamezawa-sans suggestion into usable code > > The following two items should be picked up in a second or third pass at > improving the page allocator > > 1. Working out if knowing whether pages are cold/hot on free is worth it or > not > 2. Precalculating zonelists for cpusets (Andi described how it could be done, > it's straight-forward, just will take time but it doesn't affect the > majority of users) > > Changes since V1 > o Remove the ifdef CONFIG_CPUSETS from inside get_page_from_freelist() > o Use non-lock bit operations for clearing the mlock flag > o Factor out alloc_flags calculation so it is only done once (Peter) > o Make gfp.h a bit prettier and clear-cut (Peter) > o Instead of deleting a debugging check, replace page_count() in the > free path with a version that does not check for compound pages (Nick) > o Drop the alteration for hot/cold page freeing until we know if it > helps or not > > The complexity of the page allocator has been increasing for some time > and it has now reached the point where the SLUB allocator is doing strange > tricks to avoid the page allocator. This is obviously bad as it may encourage > other subsystems to try avoiding the page allocator as well. > > This series of patches is intended to reduce the cost of the page > allocator by doing the following. > > Patches 1-3 iron out the entry paths slightly and remove stupid sanity > checks from the fast path. > > Patch 4 uses a lookup table instead of a number of branches to decide what > zones are usable given the GFP flags. > > Patch 5 tidies up some flags > > Patch 6 avoids repeated checks of the zonelist > > Patch 7 breaks the allocator up into a fast and slow path where the fast > path later becomes one long inlined function. > > Patches 8-12 avoids calculating the same things repeatedly and instead > calculates them once. > > Patches 13-14 inline parts of the allocator fast path > > Patch 15 avoids calling get_pageblock_migratetype() potentially twice on > every page free > > Patch 16 reduces the number of times interrupts are disabled by reworking > what free_page_mlock() does and not using locked versions of bit operations. > > Patch 17 avoids using the zonelist cache on non-NUMA machines > > Patch 18 simplifies some debugging checks made during alloc and free. > > Patch 19 avoids a list search in the allocator fast path. > > Running all of these through a profiler shows me the cost of page allocation > and freeing is reduced by a nice amount without drastically altering how the > allocator actually works. Excluding the cost of zeroing pages, the cost of > allocation is reduced by 25% and the cost of freeing by 12%. Again excluding > zeroing a page, much of the remaining cost is due to counters, debugging > checks and interrupt disabling. Of course when a page has to be zeroed, > the dominant cost of a page allocation is zeroing it. > > These patches reduce the text size of the kernel by 180 bytes on the one > x86-64 machine I checked. > > Range of results (positive is good) on 7 machines that completed tests. > > o Kernbench elapsed time -0.04 to 0.79% > o Kernbench system time 0 to 3.74% > o tbench -2.85% to 5.52% > o Hackbench-sockets all differences within noise > o Hackbench-pipes -2.98% to 9.11% > o Sysbench -0.04% to 5.50% > > With hackbench-pipes, only 2 machines out of 7 showed results outside of > the noise. In almost all cases the strandard deviation between runs of > hackbench-pipes was reduced with the patches. > > I still haven't run a page-allocator micro-benchmark to see what sort of > figures that gives. > > arch/ia64/hp/common/sba_iommu.c | 2 > arch/ia64/kernel/mca.c | 3 > arch/ia64/kernel/uncached.c | 3 > arch/ia64/sn/pci/pci_dma.c | 3 > arch/powerpc/platforms/cell/ras.c | 2 > arch/x86/kvm/vmx.c | 2 > drivers/misc/sgi-gru/grufile.c | 2 > drivers/misc/sgi-xp/xpc_uv.c | 2 > include/linux/cpuset.h | 2 > include/linux/gfp.h | 62 +-- > include/linux/mm.h | 1 > include/linux/mmzone.h | 8 > init/main.c | 1 > kernel/profile.c | 8 > mm/filemap.c | 2 > mm/hugetlb.c | 4 > mm/internal.h | 11 > mm/mempolicy.c | 2 > mm/migrate.c | 2 > mm/page_alloc.c | 642 +++++++++++++++++++++++++------------- > mm/slab.c | 4 > mm/slob.c | 4 > mm/vmalloc.c | 1 > 23 files changed, 490 insertions(+), 283 deletions(-) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.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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