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@xxxxxxxx>
>> ---
>> 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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