linux-kernel - Re: [PATCH] sysctl: Fix division by zero in percpu_pagelist

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Message-Id: <2C763027-307F-4BC0-8C0A-7E3D5957A4DA@linuxhacker.ru>
Date:	Tue, 3 Jun 2014 00:17:23 -0400
From:	Oleg Drokin <green@...uxhacker.ru>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org, devel@...verdev.osuosl.org,
	Rohit Seth <rohitseth@...gle.com>
Subject: Re: [PATCH] sysctl: Fix division by zero in percpu_pagelist_fraction handler

Hello!

On Jun 2, 2014, at 11:57 PM, David Rientjes wrote:
> I'm pretty sure we want to allow users to restore the kernel default 
> behavior if they've already written to this file and now want to change it 
> back.
> 
> What do you think about doing it like this instead?
> ---
> Documentation/sysctl/vm.txt |  3 ++-
> kernel/sysctl.c             |  3 +--
> mm/page_alloc.c             | 20 ++++++++++++--------
> 3 files changed, 15 insertions(+), 11 deletions(-)
> 
> diff --git a/Documentation/sysctl/vm.txt b/Documentation/sysctl/vm.txt
> --- a/Documentation/sysctl/vm.txt
> +++ b/Documentation/sysctl/vm.txt
> @@ -702,7 +702,8 @@ The batch value of each per cpu pagelist is also updated as a result.  It is
> set to pcp->high/4.  The upper limit of batch is (PAGE_SHIFT * 8)
> 
> The initial value is zero.  Kernel does not use this value at boot time to set
> -the high water marks for each per cpu page list.
> +the high water marks for each per cpu page list.  If the user writes '0' to this
> +sysctl, it will revert to this default behavior.

I think this is probably a better idea indeed.
Always good to let users return back to defaults too.

Thanks!

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