linux-kernel - Re: [PATCH v2 1/2] mm: Cap zone movable's min wmark to small value

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Date:   Thu, 25 Aug 2022 08:49:12 +0800
From:   mawupeng <mawupeng1@...wei.com>
To:     <david@...hat.com>, <akpm@...ux-foundation.org>
CC:     <mawupeng1@...wei.com>, <corbet@....net>, <mcgrof@...nel.org>,
        <keescook@...omium.org>, <yzaikin@...gle.com>,
        <songmuchun@...edance.com>, <mike.kravetz@...cle.com>,
        <osalvador@...e.de>, <rppt@...nel.org>, <surenb@...gle.com>,
        <jsavitz@...hat.com>, <linux-doc@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
        <linux-fsdevel@...r.kernel.org>, <wangkefeng.wang@...wei.com>
Subject: Re: [PATCH v2 1/2] mm: Cap zone movable's min wmark to small value



On 2022/8/24 16:10, David Hildenbrand wrote:
> On 19.08.22 11:30, Wupeng Ma wrote:
>> From: Ma Wupeng <mawupeng1@...wei.com>
>>
>> Since min_free_kbytes is based on gfp_zone(GFP_USER) which does not include
>> zone movable. However zone movable will get its min share in
>> __setup_per_zone_wmarks() which does not make any sense.
>>
>> And like highmem pages, __GFP_HIGH and PF_MEMALLOC allocations usually
>> don't need movable pages, so there is no need to assign min pages for zone
>> movable.
>>
>> Let's cap pages_min for zone movable to a small value here just link
>> highmem pages.
>>
>> Signed-off-by: Ma Wupeng <mawupeng1@...wei.com>
>> ---
>>  mm/page_alloc.c | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index e5486d47406e..ff644205370f 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -8638,7 +8638,7 @@ static void __setup_per_zone_wmarks(void)
>>  
>>  	/* Calculate total number of !ZONE_HIGHMEM pages */
>>  	for_each_zone(zone) {
>> -		if (!is_highmem(zone))
>> +		if (!is_highmem(zone) && zone_idx(zone) != ZONE_MOVABLE)
>>  			lowmem_pages += zone_managed_pages(zone);
>>  	}
>>  
>> @@ -8648,7 +8648,7 @@ static void __setup_per_zone_wmarks(void)
>>  		spin_lock_irqsave(&zone->lock, flags);
>>  		tmp = (u64)pages_min * zone_managed_pages(zone);
>>  		do_div(tmp, lowmem_pages);
>> -		if (is_highmem(zone)) {
>> +		if (is_highmem(zone) || zone_idx(zone) == ZONE_MOVABLE) {
>>  			/*
>>  			 * __GFP_HIGH and PF_MEMALLOC allocations usually don't
>>  			 * need highmem pages, so cap pages_min to a small
> 
> This kind-off makes sense to me, but I'm not completely sure about all
> implications. We most certainly should update the comment as well.

Yes, we should certainly do this.

Thanks for reviewing.

>