To: Pintu Kumar <pintu.k@samsung.com>
Cc: corbet@lwn.net, akpm@linux-foundation.org, vbabka@suse.cz,
        gorcunov@openvz.org, mhocko@suse.cz, emunson@akamai.com,
        kirill.shutemov@linux.intel.com, standby24x7@gmail.com,
        hannes@cmpxchg.org, vdavydov@parallels.com, hughd@google.com,
        minchan@kernel.org, tj@kernel.org, rientjes@google.com,
        xypron.glpk@gmx.de, dzickus@redhat.com, prarit@redhat.com,
        ebiederm@xmission.com, rostedt@goodmis.org, uobergfe@redhat.com,
        paulmck@linux.vnet.ibm.com, iamjoonsoo.kim@lge.com, ddstreet@ieee.org,
        sasha.levin@oracle.com, koct9i@gmail.com, mgorman@suse.de,
        cj@linux.com, opensource.ganesh@gmail.com, vinmenon@codeaurora.org,
        linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, linux-pm@vger.kernel.org, cpgs@samsung.com,
        pintu_agarwal@yahoo.com, vishnu.ps@samsung.com, rohit.kr@samsung.com,
        iqbal.ams@samsung.com
Subject: Re: [PATCH 1/1] kernel/sysctl.c: Add /proc/sys/vm/shrink_memory feature
In-Reply-To: Your message of "Fri, 03 Jul 2015 18:50:07 +0530."
             <1435929607-3435-1-git-send-email-pintu.k@samsung.com>
From: Valdis.Kletnieks@vt.edu
References: <1435929607-3435-1-git-send-email-pintu.k@samsung.com>
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Date: Sat, 04 Jul 2015 16:08:47 -0400
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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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