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Date: Tue, 6 Jun 2023 11:11:09 +0800
From: "Yin, Fengwei" <fengwei.yin@...el.com>
To: Hugh Dickins <hughd@...gle.com>
CC: "Liam R. Howlett" <Liam.Howlett@...cle.com>,
Peng Zhang <zhangpeng.00@...edance.com>,
<maple-tree@...ts.infradead.org>, <linux-mm@...ck.org>,
<linux-kernel@...r.kernel.org>, "Liu, Yujie" <yujie.liu@...el.com>,
Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 00/14] Reduce preallocations for maple tree
On 6/6/2023 11:08 AM, Hugh Dickins wrote:
> On Tue, 6 Jun 2023, Yin, Fengwei wrote:
>> 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.
>
> I was going to say:
> No, I did not mean that: I just meant that even developers not doing
> strict performance testing still like to keep a rough eye on performance
> changes; and historically CONFIG_DEBUG_VM has not distorted very much.
>
> But then I wonder about certain distros which (wrongly or rightly) turn
> CONFIG_DEBUG_VM on: I expect they do performance testing on their kernels.
Fair enough. Thanks for explanation.
Regards
Yin, Fengwei
>
> Hugh
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