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Date:   Tue, 6 Jun 2023 10:55:24 +0800
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Subject: Re: [PATCH 00/14] Reduce preallocations for maple tree
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To:     Hugh Dickins <hughd@google.com>,
        "Liam R. Howlett" <Liam.Howlett@oracle.com>,
        Peng Zhang <zhangpeng.00@bytedance.com>,
        <maple-tree@lists.infradead.org>, <linux-mm@kvack.org>,
        <linux-kernel@vger.kernel.org>, "Liu, Yujie" <yujie.liu@intel.com>,
        "Andrew Morton" <akpm@linux-foundation.org>
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From:   "Yin, Fengwei" <fengwei.yin@intel.com>
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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