linux-kernel - Re: [PATCH v6 1/2] mm: limit growth of 3% hardcoded other user reserve

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Date:	Wed, 27 Mar 2013 14:28:32 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Andrew Shewmaker <agshew@...il.com>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	alan@...rguk.ukuu.org.uk, simon.jeons@...il.com,
	ric.masonn@...il.com
Subject: Re: [PATCH v6 1/2] mm: limit growth of 3% hardcoded other user
 reserve

On Mon, 18 Mar 2013 17:44:42 -0400 Andrew Shewmaker <agshew@...il.com> wrote:

> Add user_reserve_kbytes knob.
> 
> Limit the growth of the memory reserved for other user
> processes to min(3% current process size, user_reserve_pages).
> 
> user_reserve_pages defaults to min(3% free pages, 128MB)

That was an epic changelog ;)

>
> ...
>
> +int __meminit init_user_reserve(void)
> +{
> +	unsigned long free_kbytes;
> +
> +	free_kbytes = global_page_state(NR_FREE_PAGES) << (PAGE_SHIFT - 10);
> +
> +	sysctl_user_reserve_kbytes = min(free_kbytes / 32, 1UL << 17);
> +	return 0;
> +}
> +module_init(init_user_reserve)

Problem is, the initial default values will become wrong if memory if
hot-added or hot-removed.

That could be fixed up by appropriate use of
register_memory_notifier(), but what would the notification handler do
if the operator has modified the value?  Proportionally scale it?
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