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Message-ID: <c0c5c013-9355-c394-afff-ed25b0c456b8@linux.alibaba.com>
Date:   Fri, 19 Aug 2022 10:47:58 +0800
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Subject: Re: [PATCH V2 1/2] mm/damon/lru_sort: Move target memory region check
 to head of func
To:     SeongJae Park <sj@kernel.org>
Cc:     akpm@linux-foundation.org, damon@lists.linux.dev,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org
References: <20220819022850.52236-1-sj@kernel.org>
From:   haoxin <xhao@linux.alibaba.com>
In-Reply-To: <20220819022850.52236-1-sj@kernel.org>
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在 2022/8/19 上午10:28, SeongJae Park 写道:
> Hi Xin,
>
>> 在 2022/8/19 上午1:11, SeongJae Park 写道:
>>> Hi Xin,
>>>
>>>
>>> On Thu, 18 Aug 2022 18:57:31 +0800 Xin Hao <xhao@linux.alibaba.com> wrote:
>>>
>>>> In damon_lru_sort_apply_parameters(), if "monitor_region_start"
>>>> and "monitor_region_end" is not a valid physical address range,
>>>> There no need to run the remainder codes in it.
>>> The function, 'damon_lru_sort_apply_parameters()', checks validity of
>>> parameters and construct the DAMON context one by one.  For example,
>>> 'damon_set_attrs()' returns an error if the parameters are invalid.  So the
>>> intended flow is,
>>>
>>> 1. check DAMON attributes parameters,
>>> 2. apply DAMON attributes parameters,
>>> 3. check scheme parameters,
>>> 4. apply scheme parameters,
>>> 5. check target region parameters, and
>>> 6. apply target region parameters.
>>>
>>> Therefore what this patch does is making the target regions validity check to
>>> be done earlier than validity checks of other parameters.  There is no special
>>> reason to check the region earlier than others.  Also, this change makes the
>>> flow of the function a little bit weird in my humble opinion, as the flow will
>>> be
>>>
>>> 1. check target region parameters,
>>> 2. check DAMON attributes parameters,
>>> 3. apply DAMON attributes parameters,
>>> 4. check scheme parameters,
>>> 5. apply scheme parameters, and
>>> 6. apply target region parameters.
>> Ok, understand what you mean,   my fix looks ugly,  buy any apply above
>> are not not necessary if one of them checks failed, why not check all
>> fisrt and then apply them, like this:
>>
>> 1. check target region parameters,
>>
>> 2. check DAMON attributes parameters,
>>
>> 3. check scheme parameters,
> The parameter values could be changed by users after the check, so we should
> cache those somewhere anyway.  In other words, we cache those in the DAMON
> context.  Therefore I think the above works were not totally waste of the time.
> Also, because the parameters applying functions like 'damon_set_attrs()' does
> the check and applying of the parameters together, I feel like current flow is
> natural.

Ok,  Thank you for your detailed  explain, just keep it. but there still 
a problem in damon_lru_sort_apply_parameters

if (!monitor_region_start && !monitor_region_end &&
		!get_monitoring_region(&monitor_region_start,
			&monitor_region_end))

if (!monitor_region_start || !monitor_region_end ||
		!get_monitoring_region(&monitor_region_start,
			&monitor_region_end))

the '&&' should fix to '||',  anyone checks fail, it should return ?


>