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

[PINTU KUMAR]

> -----Original Message-----
> From: Heinrich Schuchardt [mailto:xypron.glpk@xxxxxx]
> Sent: Friday, July 03, 2015 10:51 PM
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> Subject: Re: [PATCH 1/1] kernel/sysctl.c: Add /proc/sys/vm/shrink_memory
> feature
> 
> On 03.07.2015 15:20, Pintu Kumar wrote:
> > This patch provides 2 things:
> > 1. Add new control called shrink_memory in /proc/sys/vm/.
> > This control can be used to aggressively reclaim memory system-wide in
> > one shot from the user space. A value of 1 will instruct the kernel to
> > reclaim as much as totalram_pages in the system.
> > Example: echo 1 > /proc/sys/vm/shrink_memory
> >
> > 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.
> >
> > The detailed paper was presented in Embedded Linux Conference,
> > Mar-2015 http://events.linuxfoundation.org/sites/events/files/slides/
> > %5BELC-2015%5D-System-wide-Memory-Defragmenter.pdf
> >
> > Scenarios were this can be used and helpful are:
> > 1) Can be invoked just after system boot-up is finished.
> > 2) Can be invoked just before entering entire system suspend.
> > 3) Can be invoked from kernel when order-4 pages starts failing.
> > 4) Can be helpful to completely avoid or delay the kerenl OOM condition.
> > 5) Can be developed as a system-tool to quickly defragment entire system
> >    from user space, without the need to kill any application.
> >
> > Signed-off-by: Pintu Kumar <pintu.k@xxxxxxxxxxx>
> > ---
> >  Documentation/sysctl/vm.txt |   16 ++++++++++++++++
> >  include/linux/swap.h        |    7 +++++++
> >  kernel/sysctl.c             |    9 +++++++++
> >  mm/Kconfig                  |    8 ++++++++
> >  mm/vmscan.c                 |   23 +++++++++++++++++++++--
> >  5 files changed, 61 insertions(+), 2 deletions(-)
> >
> > diff --git a/Documentation/sysctl/vm.txt b/Documentation/sysctl/vm.txt
> > index 9832ec5..a959ad1 100644
> > --- a/Documentation/sysctl/vm.txt
> > +++ b/Documentation/sysctl/vm.txt
> > @@ -54,6 +54,7 @@ Currently, these files are in /proc/sys/vm:
> >  - page-cluster
> >  - panic_on_oom
> >  - percpu_pagelist_fraction
> > +- shrink_memory
> >  - stat_interval
> >  - swappiness
> >  - user_reserve_kbytes
> > @@ -718,6 +719,21 @@ sysctl, it will revert to this default behavior.
> >
> >  ==============================================================
> >
> > +shrink_memory
> > +
> > +This control is available only when CONFIG_SHRINK_MEMORY is set. This
> > +control can be used to aggressively reclaim memory system-wide in one
> > +shot. A value of
> > +1 will instruct the kernel to reclaim as much as totalram_pages in the
system.
> > +For example, to reclaim all memory system-wide we can do:
> > +# echo 1 > /proc/sys/vm/shrink_memory
> 
> The API should be as restrictive as possible to allow for extensibility.
> 
> You describe "1" as the only used value. So, please add here:
> 
> "If any other value than 1 is written to shrink_memory an error EINVAL
occurs."
> 

Ok, I will handle this error case in next patch set.
Actual, I did exactly like compact_memory, so I made this way.

> > +
> > +For more information about this control, please visit the following
> > +presentation in embedded linux conference, 2015.
> > +http://events.linuxfoundation.org/sites/events/files/slides/
> > +%5BELC-2015%5D-System-wide-Memory-Defragmenter.pdf
> > +
> > +==============================================================
> > +
> >  stat_interval
> >
> >  The time interval between which vm statistics are updated.  The
> > default diff --git a/include/linux/swap.h b/include/linux/swap.h index
> > 9a7adfb..6505b0b 100644
> > --- a/include/linux/swap.h
> > +++ b/include/linux/swap.h
> > @@ -333,6 +333,13 @@ extern int vm_swappiness;  extern int
> > remove_mapping(struct address_space *mapping, struct page *page);
> > extern unsigned long vm_total_pages;
> >
> > +#ifdef CONFIG_SHRINK_MEMORY
> > +extern int sysctl_shrink_memory;
> > +extern int sysctl_shrinkmem_handler(struct ctl_table *table, int write,
> > +		void __user *buffer, size_t *length, loff_t *ppos); #endif
> > +
> > +
> >  #ifdef CONFIG_NUMA
> >  extern int zone_reclaim_mode;
> >  extern int sysctl_min_unmapped_ratio; diff --git a/kernel/sysctl.c
> > b/kernel/sysctl.c index c566b56..2895099 100644
> > --- a/kernel/sysctl.c
> > +++ b/kernel/sysctl.c
> > @@ -1351,6 +1351,15 @@ static struct ctl_table vm_table[] = {
> >  	},
> >
> >  #endif /* CONFIG_COMPACTION */
> > +#ifdef CONFIG_SHRINK_MEMORY
> > +	{
> > +		.procname	= "shrink_memory",
> > +		.data		= &sysctl_shrink_memory,
> > +		.maxlen		= sizeof(int),
> > +		.mode		= 0200,
> > +		.proc_handler	= sysctl_shrinkmem_handler,
> 
> Supply the value limits.
> 
> int min_shrink_memory = 1;
> int max_shrink_memory = 1;
> 
> .extra1 = &min_shrink_memory,
> .extra2 = &max_shrink_memory,
> 
Ok, I will include this value as well in the new patch set.

> > +	},
> > +#endif
> >  	{
> >  		.procname	= "min_free_kbytes",
> >  		.data		= &min_free_kbytes,
> > diff --git a/mm/Kconfig b/mm/Kconfig
> > index b3a60ee..8e04bd9 100644
> > --- a/mm/Kconfig
> > +++ b/mm/Kconfig
> > @@ -657,3 +657,11 @@ config DEFERRED_STRUCT_PAGE_INIT
> >  	  when kswapd starts. This has a potential performance impact on
> >  	  processes running early in the lifetime of the systemm until kswapd
> >  	  finishes the initialisation.
> > +
> > +config SHRINK_MEMORY
> > +	bool "Allow for system-wide shrinking of memory"
> > +	default n
> > +	depends on MMU
> > +	help
> > +	  It enables support for system-wide memory reclaim in one shot using
> > +	  echo 1 > /proc/sys/vm/shrink_memory.
> > diff --git a/mm/vmscan.c b/mm/vmscan.c index c8d8282..837b88d 100644
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -3557,7 +3557,7 @@ void wakeup_kswapd(struct zone *zone, int order,
> enum zone_type classzone_idx)
> >  	wake_up_interruptible(&pgdat->kswapd_wait);
> >  }
> >
> > -#ifdef CONFIG_HIBERNATION
> > +#if defined CONFIG_HIBERNATION || CONFIG_SHRINK_MEMORY
> >  /*
> >   * Try to free `nr_to_reclaim' of memory, system-wide, and return the
number
> of
> >   * freed pages.
> > @@ -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
> >  		.priority = DEF_PRIORITY,
> >  		.may_writepage = 1,
> >  		.may_unmap = 1,
> >  		.may_swap = 1,
> > -		.hibernation_mode = 1,
> >  	};
> >  	struct zonelist *zonelist = node_zonelist(numa_node_id(), sc.gfp_mask);
> >  	struct task_struct *p = current;
> > @@ -3597,6 +3602,20 @@ unsigned long shrink_all_memory(unsigned long
> > nr_to_reclaim)  }  #endif /* CONFIG_HIBERNATION */
> >
> > +#ifdef CONFIG_SHRINK_MEMORY
> > +int sysctl_shrink_memory;
> > +/* This is the entry point for system-wide shrink memory
> > ++via /proc/sys/vm/shrink_memory */
> > +int sysctl_shrinkmem_handler(struct ctl_table *table, int write,
> > +		void __user *buffer, size_t *length, loff_t *ppos) {
> 
> Check if *buffer contains "1". If the value is not "1" return -EINVAL.
> 
> The check can be done using function proc_dointvec_minmax().
> 

Ok, I will include this case also in the new patch set.
Thanks for the review and suggestions.

> Best regards
> 
> Heinrich Schuchardt
> 
> > +	if (write)
> > +		shrink_all_memory(totalram_pages);
> > +
> > +	return 0;
> > +}
> > +#endif
> > +
> >  /* It's optimal to keep kswapds on the same CPUs as their memory, but
> >     not required for correctness.  So if the last cpu in a node goes
> >     away, we get changed to run anywhere: as the first one comes back,
> >

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