Re: [PATCH] mm/min_free_kbytes: modify min_free_kbytes calculation rules

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liuq <liuq131@xxxxxxxxxxxxxxx> writes:

> 在 2023/6/19 11:25, Huang, Ying 写道:
>> Added Mel and Vlastimil.
>>
>> liuq <liuq131@xxxxxxxxxxxxxxx> writes:
>>
>>> The current calculation of min_free_kbytes only uses ZONE_DMA and
>>> ZONE_NORMAL pages,but the ZONE_MOVABLE zone->_watermark[WMARK_MIN]
>>> will also divide part of min_free_kbytes.This will cause the min
>>> watermark of ZONE_NORMAL to be too small in the presence of ZONE_MOVEABLE.
>> This seems like a real problem per my understanding.  Can you show the
>> contents of /proc/zoneinfo on a problem system?
>>
>> But, per my understanding, min_free_kbytes are used for __GFP_HIGH and
>> PF_MEMALLOC allocations.  While ZONE_MOVABLE will not be used for them
>> usually.  So I think we should treat ZONE_MOVABLE as ZONE_HIGHMEM in
>> __setup_per_zone_wmarks().
>>
>> Best Regards,
>> Huang, Ying
> On my testing machine with 16GB of memory (transparent hugepage is
> turned off by default), when movable zone is not configured,
> min_free_kbytes  is 15806 (15806*15806/16=15614352kbytes, approximatel
> y 16G).
> The detailed info is as follows:
> [root@lq-workstation ~]# cat /proc/cmdline
> BOOT_IMAGE=/vmlinuz-6.2.0-rc7-00018-g0983f6bf2bfc-dirty
> root=/dev/mapper/ctyunos00-root ro resume=/dev/mapper/ctyunos00-swap
> rd.lvm.lv=ctyunos00/root rd.lvm.lv=ctyunos00/swap crashkernel=512M
> [root@lq-workstation ~]#  cat /proc/zoneinfo |grep -A 5 min
>         min      3
>         low      6
>         high     9
>         spanned  4095
>         present  3998
>         managed  3840
> --
>         min      328
>         low      652
>         high     976
>         spanned  1044480
>         present  478802
>         managed  330969
> --
>         min      3618
>         low      7193
>         high     10768
>         spanned  3655680
>         present  3655680
>         managed  3575787
> --
>         min      0
>         low      0
>         high     0
>         spanned  0
>         present  0
>         managed  0
> [root@lq-workstation ~]# cat /proc/sys/vm/min_free_kbytes
> 15806
>
> If movablecore=12G is configured, at this time, min_free_kbytes is
> 7326 (7326 * 7326/16=3354392, approximately 16G-12G)
> The detailed info is as follows:
> [root@lq-workstation ~]# cat /proc/cmdline
> BOOT_IMAGE=/vmlinuz-6.2.0-rc7-00018-g0983f6bf2bfc-dirty
> root=/dev/mapper/ctyunos00-root ro resume=/dev/mapper/ctyunos00-swap
> rd.lvm.lv=ctyunos00/root rd.lvm.lv=ctyunos00/swap crashkernel=512M
> movablecore=12G
> [root@lq-workstation ~]# cat /proc/zoneinfo |grep -A 5 min
>         min      1
>         low      4
>         high     7
>         spanned  4095
>         present  3998
>         managed  3840
> --
>         min      152
>         low      476
>         high     800
>         spanned  1044480
>         present  478802
>         managed  330969
> --
>         min      239
>         low      748
>         high     1257
>         spanned  509952
>         present  509952
>         managed  509952
> --
>         min      1437
>         low      4502
>         high     7567
>         spanned  3145728
>         present  3145728
>         managed  3065833
> [root@lq-workstation ~]# cat /proc/sys/vm/min_free_kbytes
> 7326

Thank you very much for data!  Per my understanding, this verifies a
real problem.

You patch can fix the too small "min" for ZONE_NORMAL/ZONE_DMA.  But,
IMHO, it increases "min" for ZONE_MOVABLE unnecessarily.  Because we
don't allocate from ZONE_MOVABLE for __GFP_HIGH or PF_MEMALLOC
allocations.  So, IMHO, we should treat ZONE_MOVABLE as ZONE_HIGHMEM in
__setup_per_zone_wmarks().

Best Regards,
Huang, Ying

> After this patch is added, the configuration of the movable zone no
> longer affects the size of the min_free_kbytes, which is only affected
> by the size of the available memory.
>>> Signed-off-by: liuq <liuq131@xxxxxxxxxxxxxxx>
>>> ---
>>>   include/linux/mm.h |  1 +
>>>   mm/khugepaged.c    |  2 +-
>>>   mm/page_alloc.c    | 15 ++++++++++++++-
>>>   3 files changed, 16 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/include/linux/mm.h b/include/linux/mm.h
>>> index cf3d0d673f6b..1f91d035bcaf 100644
>>> --- a/include/linux/mm.h
>>> +++ b/include/linux/mm.h
>>> @@ -863,6 +863,7 @@ void split_page(struct page *page, unsigned int order);
>>>   void folio_copy(struct folio *dst, struct folio *src);
>>>     unsigned long nr_free_buffer_pages(void);
>>> +unsigned long nr_free_pagecache_pages(void);
>>>     /*
>>>    * Compound pages have a destructor function.  Provide a
>>> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
>>> index 16be62d493cd..6632264b951c 100644
>>> --- a/mm/khugepaged.c
>>> +++ b/mm/khugepaged.c
>>> @@ -2342,7 +2342,7 @@ static void set_recommended_min_free_kbytes(void)
>>>     	/* don't ever allow to reserve more than 5% of the lowmem */
>>>   	recommended_min = min(recommended_min,
>>> -			      (unsigned long) nr_free_buffer_pages() / 20);
>>> +			      (unsigned long) nr_free_pagecache_pages() / 20);
>>>   	recommended_min <<= (PAGE_SHIFT-10);
>>>     	if (recommended_min > min_free_kbytes) {
>>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>>> index e008a3df0485..489b564526dd 100644
>>> --- a/mm/page_alloc.c
>>> +++ b/mm/page_alloc.c
>>> @@ -5775,6 +5775,19 @@ unsigned long nr_free_buffer_pages(void)
>>>   }
>>>   EXPORT_SYMBOL_GPL(nr_free_buffer_pages);
>>>   +/**
>>> + * nr_free_pagecache_pages - count number of pages beyond high watermark
>>> + *
>>> + * nr_free_pagecache_pages() counts the number of pages which are beyond the
>>> + * high watermark within all zones.
>>> + *
>>> + * Return: number of pages beyond high watermark within all zones.
>>> + */
>>> +unsigned long nr_free_pagecache_pages(void)
>>> +{
>>> +	return nr_free_zone_pages(gfp_zone(GFP_HIGHUSER_MOVABLE));
>>> +}
>>> +
>>>   static inline void show_node(struct zone *zone)
>>>   {
>>>   	if (IS_ENABLED(CONFIG_NUMA))
>>> @@ -8651,7 +8664,7 @@ void calculate_min_free_kbytes(void)
>>>   	unsigned long lowmem_kbytes;
>>>   	int new_min_free_kbytes;
>>>   -	lowmem_kbytes = nr_free_buffer_pages() * (PAGE_SIZE >> 10);
>>> +	lowmem_kbytes = nr_free_pagecache_pages() * (PAGE_SIZE >> 10);
>>>   	new_min_free_kbytes = int_sqrt(lowmem_kbytes * 16);
>>>     	if (new_min_free_kbytes > user_min_free_kbytes)




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