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Date:   Fri, 24 Nov 2017 11:15:24 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Michal Hocko <mhocko@...nel.org>,
        Peter Enderborg <peter.enderborg@...y.com>
Cc:     linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
        Jonathan Corbet <corbet@....net>,
        "Luis R . Rodriguez" <mcgrof@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Alex Deucher <alexander.deucher@....com>,
        "David S . Miller" <davem@...emloft.net>,
        Harry Wentland <Harry.Wentland@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Tony Cheng <Tony.Cheng@....com>,
        David Rientjes <rientjes@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jan Kara <jack@...e.cz>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        Ross Zwisler <ross.zwisler@...ux.intel.com>,
        Matthew Wilcox <willy@...ux.intel.com>,
        Hugh Dickins <hughd@...gle.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Kemi Wang <kemi.wang@...el.com>,
        YASUAKI ISHIMATSU <yasu.isimatu@...il.com>,
        Nikolay Borisov <nborisov@...e.com>,
        Mel Gorman <mgorman@...e.de>,
        Pavel Tatashin <pasha.tatashin@...cle.com>,
        Linux API <linux-api@...r.kernel.org>
Subject: Re: [PATCH] mm:Add watermark slope for high mark

On 11/24/2017 11:14 AM, Michal Hocko wrote:
> On Fri 24-11-17 11:07:07, Peter Enderborg wrote:
>> When tuning the watermark_scale_factor to reduce stalls and compactions
>> the high mark is also changed, it changed a bit too much. So this
>> patch introduces a slope that can reduce this overhead a bit, or
>> increase it if needed.
> 
> This doesn't explain what is the problem, why it is a problem and why we
> need yet another tuning to address it. Users shouldn't really care about
> internal stuff like watermark tuning for each watermark independently.
> This looks like a gross hack. Please start over with the problem
> description and then we can move on to an approapriate fix. Piling up
> tuning knobs to workaround problems is simply not acceptable.

Agreed. Also if you send a patch adding userspace API or a tuning knob,
please CC linux-api mailing list (did that for this reply).

>> Signed-off-by: Peter Enderborg <peter.enderborg@...y.com>
>> ---
>>  Documentation/sysctl/vm.txt | 15 +++++++++++++++
>>  include/linux/mm.h          |  1 +
>>  include/linux/mmzone.h      |  2 ++
>>  kernel/sysctl.c             |  9 +++++++++
>>  mm/page_alloc.c             |  6 +++++-
>>  5 files changed, 32 insertions(+), 1 deletion(-)
>>
>> diff --git a/Documentation/sysctl/vm.txt b/Documentation/sysctl/vm.txt
>> index eda628c..aecff6c 100644
>> --- a/Documentation/sysctl/vm.txt
>> +++ b/Documentation/sysctl/vm.txt
>> @@ -62,6 +62,7 @@ Currently, these files are in /proc/sys/vm:
>>  - user_reserve_kbytes
>>  - vfs_cache_pressure
>>  - watermark_scale_factor
>> +- watermark_high_factor_slope
>>  - zone_reclaim_mode
>>  
>>  ==============================================================
>> @@ -857,6 +858,20 @@ that the number of free pages kswapd maintains for latency reasons is
>>  too small for the allocation bursts occurring in the system. This knob
>>  can then be used to tune kswapd aggressiveness accordingly.
>>  
>> +=============================================================
>> +
>> +watermark_high_factor_slope:
>> +
>> +This factor is high mark for watermark_scale_factor.
>> +The unit is in percent.
>> +Max value is 1000 and min value is 100. (High watermark is the same as
>> +low water mark) Low watermark is min_wmark_pages + watermark_scale_factor.
>> +and high watermark is
>> +min_wmark_pages+(watermark_scale_factor * watermark_high_factor_slope).
>> +
>> +The default value is 200.
>> +
>> +
>>  ==============================================================
>>  
>>  zone_reclaim_mode:
>> diff --git a/include/linux/mm.h b/include/linux/mm.h
>> index 7661156..c89536b 100644
>> --- a/include/linux/mm.h
>> +++ b/include/linux/mm.h
>> @@ -2094,6 +2094,7 @@ extern void zone_pcp_reset(struct zone *zone);
>>  /* page_alloc.c */
>>  extern int min_free_kbytes;
>>  extern int watermark_scale_factor;
>> +extern int watermark_high_factor_slope;
>>  
>>  /* nommu.c */
>>  extern atomic_long_t mmap_pages_allocated;
>> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
>> index 67f2e3c..91bf842 100644
>> --- a/include/linux/mmzone.h
>> +++ b/include/linux/mmzone.h
>> @@ -886,6 +886,8 @@ int min_free_kbytes_sysctl_handler(struct ctl_table *, int,
>>  					void __user *, size_t *, loff_t *);
>>  int watermark_scale_factor_sysctl_handler(struct ctl_table *, int,
>>  					void __user *, size_t *, loff_t *);
>> +//int watermark_high_factor_tilt_sysctl_handler(struct ctl_table *, int,
>> +//					void __user *, size_t *, loff_t *);
>>  extern int sysctl_lowmem_reserve_ratio[MAX_NR_ZONES-1];
>>  int lowmem_reserve_ratio_sysctl_handler(struct ctl_table *, int,
>>  					void __user *, size_t *, loff_t *);
>> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
>> index 2fb4e27..83c48c9 100644
>> --- a/kernel/sysctl.c
>> +++ b/kernel/sysctl.c
>> @@ -1444,6 +1444,15 @@ static struct ctl_table vm_table[] = {
>>  		.extra2		= &one_thousand,
>>  	},
>>  	{
>> +		.procname	= "watermark_high_factor_slope",
>> +		.data		= &watermark_high_factor_slope,
>> +		.maxlen		= sizeof(watermark_high_factor_slope),
>> +		.mode		= 0644,
>> +		.proc_handler	= watermark_scale_factor_sysctl_handler,
>> +		.extra1		= &one_hundred,
>> +		.extra2		= &one_thousand,
>> +	},
>> +	{
>>  		.procname	= "percpu_pagelist_fraction",
>>  		.data		= &percpu_pagelist_fraction,
>>  		.maxlen		= sizeof(percpu_pagelist_fraction),
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index 48b5b01..3dc50ff 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -263,6 +263,7 @@ compound_page_dtor * const compound_page_dtors[] = {
>>  int min_free_kbytes = 1024;
>>  int user_min_free_kbytes = -1;
>>  int watermark_scale_factor = 10;
>> +int watermark_high_factor_slope = 200;
>>  
>>  static unsigned long __meminitdata nr_kernel_pages;
>>  static unsigned long __meminitdata nr_all_pages;
>> @@ -6989,6 +6990,7 @@ static void __setup_per_zone_wmarks(void)
>>  
>>  	for_each_zone(zone) {
>>  		u64 tmp;
>> +		u64 tmp_high;
>>  
>>  		spin_lock_irqsave(&zone->lock, flags);
>>  		tmp = (u64)pages_min * zone->managed_pages;
>> @@ -7026,7 +7028,9 @@ static void __setup_per_zone_wmarks(void)
>>  				      watermark_scale_factor, 10000));
>>  
>>  		zone->watermark[WMARK_LOW]  = min_wmark_pages(zone) + tmp;
>> -		zone->watermark[WMARK_HIGH] = min_wmark_pages(zone) + tmp * 2;
>> +		tmp_high = mult_frac(tmp, watermark_high_factor_slope, 100);
>> +		zone->watermark[WMARK_HIGH] = min_wmark_pages(zone) + tmp_high;
>> +
>>  
>>  		spin_unlock_irqrestore(&zone->lock, flags);
>>  	}
>> -- 
>> 2.7.4
>>
> 

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