linux-kernel - Re: missing madvise functionality

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Message-ID: <46154226.6080300@redhat.com>
Date:	Thu, 05 Apr 2007 14:38:30 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Nick Piggin <nickpiggin@...oo.com.au>
CC:	Ulrich Drepper <drepper@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Jakub Jelinek <jakub@...hat.com>,
	Linux Memory Management <linux-mm@...ck.org>
Subject: Re: missing madvise functionality

Nick Piggin wrote:

> Oh, also: something like this patch would help out MADV_DONTNEED, as it
> means it can run concurrently with page faults. I think the locking will
> work (but needs forward porting).

Ironically, your patch decreases throughput on my quad core
test system, with Jakub's test case.

MADV_DONTNEED, my patch, 10000 loops  (14k context switches/second)

real    0m34.890s
user    0m17.256s
sys     0m29.797s

MADV_DONTNEED, my patch & your patch, 10000 loops  (50 context 
switches/second)

real    1m8.321s
user    0m20.840s
sys     1m55.677s

I suspect it's moving the contention onto the page table lock,
in zap_pte_range().  I guess that the thread private memory
areas must be living right next to each other, in the same
page table lock regions :)

For more real world workloads, like the MySQL sysbench one,
I still suspect that your patch would improve things.

Time to move back to debugging other stuff, though.

Andrew, it would be nice if our patches could cook in -mm
for a while.  Want me to change anything before submitting?

-- 
Politics is the struggle between those who want to make their country
the best in the world, and those who believe it already is.  Each group
calls the other unpatriotic.
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