linux-kernel - Re: [Stable-review] [08/45] mm, x86: Saving vmcore with non-lazy freeing of vmas

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Date:	Sat, 20 Nov 2010 02:16:12 +0000
From:	Ben Hutchings <ben@...adent.org.uk>
To:	Greg KH <gregkh@...e.de>
Cc:	linux-kernel@...r.kernel.org, stable@...nel.org,
	Ingo Molnar <mingo@...e.hu>, kexec@...ts.infradead.org,
	Cliff Wickman <cpw@....com>, akpm@...ux-foundation.org,
	torvalds@...ux-foundation.org, stable-review@...nel.org,
	alan@...rguk.ukuu.org.uk
Subject: Re: [Stable-review] [08/45] mm, x86: Saving vmcore with non-lazy
 freeing of vmas

On Fri, 2010-11-19 at 13:42 -0800, Greg KH wrote:
> 2.6.32-stable review patch.  If anyone has any objections, please let us know.
> 
> ------------------
> 
> From: Cliff Wickman <cpw@....com>
> 
> commit 3ee48b6af49cf534ca2f481ecc484b156a41451d upstream.
> 
> During the reading of /proc/vmcore the kernel is doing
> ioremap()/iounmap() repeatedly. And the buildup of un-flushed
> vm_area_struct's is causing a great deal of overhead. (rb_next()
> is chewing up most of that time).
> 
> This solution is to provide function set_iounmap_nonlazy(). It
> causes a subsequent call to iounmap() to immediately purge the
> vma area (with try_purge_vmap_area_lazy()).
> 
> With this patch we have seen the time for writing a 250MB
> compressed dump drop from 71 seconds to 44 seconds.
[...]

Useful, but it doesn't seem to meet the criteria for stable updates.

Ben.

-- 
Ben Hutchings
Once a job is fouled up, anything done to improve it makes it worse.

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