Re: [PATCH 1/1] kernel/sysctl.c: Add /proc/sys/vm/shrink_memory feature

[PINTU KUMAR <pintu_agarwal@yahoo.com>]

----- Original Message -----
> From: "Valdis.Kletnieks@vt.edu" <Valdis.Kletnieks@vt.edu>
> 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
> Sent: Sunday, 5 July 2015 1:38 AM
> 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?

> 


Ok, got it. Thanks for pointing this out.
I will handle HIBERNATION & SHRINK_MEMORY case and send again.
Do you have any special suggestions on how this can be handled?

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