linux-kernel - Re: [PATCH v1 1/1] mm/vmalloc.c: Fix percpu free VM area search criteria

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Date:   Tue, 30 Jul 2019 13:54:06 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Uladzislau Rezki <urezki@...il.com>,
        sathyanarayanan.kuppuswamy@...ux.intel.com
Cc:     akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 1/1] mm/vmalloc.c: Fix percpu free VM area search
 criteria

On 7/30/19 1:46 PM, Uladzislau Rezki wrote:
>> +		/*
>> +		 * If required width exeeds current VA block, move
>> +		 * base downwards and then recheck.
>> +		 */
>> +		if (base + end > va->va_end) {
>> +			base = pvm_determine_end_from_reverse(&va, align) - end;
>> +			term_area = area;
>> +			continue;
>> +		}
>> +
>>  		/*
>>  		 * If this VA does not fit, move base downwards and recheck.
>>  		 */
>> -		if (base + start < va->va_start || base + end > va->va_end) {
>> +		if (base + start < va->va_start) {
>>  			va = node_to_va(rb_prev(&va->rb_node));
>>  			base = pvm_determine_end_from_reverse(&va, align) - end;
>>  			term_area = area;
>> -- 
>> 2.21.0
>>
> I guess it is NUMA related issue, i mean when we have several
> areas/sizes/offsets. Is that correct?

I don't think NUMA has anything to do with it.  The vmalloc() area
itself doesn't have any NUMA properties I can think of.  We don't, for
instance, partition it into per-node areas that I know of.

I did encounter this issue on a system with ~100 logical CPUs, which is
a moderate amount these days.