linux-kernel - Re: [PATCH 1/1] kernel/sysctl.c: Add /proc/sys/vm/shrink

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Message-ID: <169308.1436040527@turing-police.cc.vt.edu>
Date:	Sat, 04 Jul 2015 16:08:47 -0400
From:	Valdis.Kletnieks@...edu
To:	Pintu Kumar <pintu.k@...sung.com>
Cc:	corbet@....net, akpm@...ux-foundation.org, vbabka@...e.cz,
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Subject: Re: [PATCH 1/1] kernel/sysctl.c: Add /proc/sys/vm/shrink_memory feature

On Fri, 03 Jul 2015 18:50:07 +0530, Pintu Kumar said:
> This patch provides 2 things:

> 2. Enable shrink_all_memory API in kernel with new CONFIG_SHRINK_MEMORY.
> Currently, shrink_all_memory function is used only during hibernation.
> With the new config we can make use of this API for non-hibernation case
> also without disturbing the hibernation case.

> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c

> @@ -3571,12 +3571,17 @@ unsigned long shrink_all_memory(unsigned long nr_to_reclaim)
>  	struct reclaim_state reclaim_state;
>  	struct scan_control sc = {
>  		.nr_to_reclaim = nr_to_reclaim,
> +#ifdef CONFIG_SHRINK_MEMORY
> +		.gfp_mask = (GFP_HIGHUSER_MOVABLE | GFP_RECLAIM_MASK),
> +		.hibernation_mode = 0,
> +#else
>  		.gfp_mask = GFP_HIGHUSER_MOVABLE,
> +		.hibernation_mode = 1,
> +#endif


That looks like a bug just waiting to happen.  What happens if we
call an actual hibernation mode in a SHRINK_MEMORY=y kernel, and it finds
an extra gfp mask bit set, and hibernation_mode set to an unexpected value?

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