Re: [PATCH 00/14] Reduce preallocations for maple tree

[Yin, Fengwei]

Hi Huge,

On 6/6/2023 10:41 AM, Hugh Dickins wrote:
> On Mon, 5 Jun 2023, Liam R. Howlett wrote:
>>
>> You mean "mm: update validate_mm() to use vma iterator" here I guess.  I
>> have it as a different commit id in my branch.
>>
>> I 'restored' some of the checking because I was able to work around not
>> having the mt_dump() definition with the vma iterator.  I'm now
>> wondering how wide spread CONFIG_DEBUG_VM is used and if I should not
>> have added these extra checks.
> 
> Most CONFIG_DEBUG_VM checks are quite cheap, mostly VM_BUG_ONs for
Indeed. I had CONFIG_DEBUG_VM enabled and didn't see surprise perf report.


> easily checked conditions.  If validate_mm() is still the kind of thing
> it used to be, checking through every vma on every mmap operation, please
> don't bring that into CONFIG_DEBUG_VM - it distorts performance too much,
> so always used to be under a separate CONFIG_DEBUG_VM_RB instead.
So does this mean CONFIG_DEBUG_VM is allowed to be enabled for performance
testing? Thanks.


Regards
Yin, Fengwei

> 
> Hugh