linux-kernel - Re: [PATCH 00/22] Cleanup and optimise the page allocator V7

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Date:	Mon, 27 Apr 2009 15:38:46 +0100
From:	Mel Gorman <mel@....ul.ie>
To:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>
Cc:	Linux Memory Management List <linux-mm@...ck.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Nick Piggin <npiggin@...e.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Lin Ming <ming.m.lin@...el.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 00/22] Cleanup and optimise the page allocator V7

On Mon, Apr 27, 2009 at 03:58:39PM +0800, Zhang, Yanmin wrote:
> On Wed, 2009-04-22 at 14:53 +0100, Mel Gorman wrote:
> > Here is V7 of the cleanup and optimisation of the page allocator and
> > it should be ready for wider testing. Please consider a possibility for
> > merging as a Pass 1 at making the page allocator faster. Other passes will
> > occur later when this one has had a bit of exercise. This patchset is based
> > on mmotm-2009-04-17 and I've tested it successfully on a small number of
> > machines.
> We ran some performance benchmarks against V7 patch on top of 2.6.30-rc3.
> It seems some counters in kernel are incorrect after we run some ffsb (disk I/O benchmark)
> and swap-cp (a simple swap memory testing by cp on tmpfs). Free memory is bigger than
> total memory.
> 

oops. Can you try this patch please?

==== CUT HERE ====

Properly account for freed pages in free_pages_bulk() and when allocating high-order pages in buffered_rmqueue()

free_pages_bulk() updates the number of free pages in the zone but it is
assuming that the pages being freed are order-0. While this is currently
always true, it's wrong to assume the order is 0. This patch fixes the
problem.

buffered_rmqueue() is not updating NR_FREE_PAGES when allocating pages with
__rmqueue(). This means that any high-order allocation will appear to increase
the number of free pages leading to the situation where free pages appears to
exceed available RAM. This patch accounts for those allocated pages properly.

This is a candidate fix to the patch
page-allocator-update-nr_free_pages-only-as-necessary.patch. It has yet to be
verified as fixing a problem where the free pages count is getting corrupted.

Signed-off-by: Mel Gorman <mel@....ul.ie>
---
 mm/page_alloc.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 3db5f57..dd69593 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -545,7 +545,7 @@ static void free_pages_bulk(struct zone *zone, int count,
 	zone_clear_flag(zone, ZONE_ALL_UNRECLAIMABLE);
 	zone->pages_scanned = 0;
 
-	__mod_zone_page_state(zone, NR_FREE_PAGES, count);
+	__mod_zone_page_state(zone, NR_FREE_PAGES, count << order);
 	while (count--) {
 		struct page *page;
 
@@ -1151,6 +1151,7 @@ again:
 	} else {
 		spin_lock_irqsave(&zone->lock, flags);
 		page = __rmqueue(zone, order, migratetype);
+		__mod_zone_page_state(zone, NR_FREE_PAGES, -(i << order));
 		spin_unlock(&zone->lock);
 		if (!page)
 			goto failed;
--
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