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From:   SeongJae Park <sj@kernel.org>
To:     haoxin <xhao@linux.alibaba.com>
Cc:     SeongJae Park <sj@kernel.org>, akpm@linux-foundation.org,
        damon@lists.linux.dev, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH V2 1/2] mm/damon/lru_sort: Move target memory region check to head of func
Date:   Thu, 18 Aug 2022 21:52:04 -0700
Message-Id: <20220819045204.21834-1-sj@kernel.org>
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On Fri, 19 Aug 2022 10:47:58 +0800 haoxin <xhao@linux.alibaba.com> wrote:

> 
> 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 ?

No.  The code is for setting the monitoring region as the biggest System RAM
resource only if the user didn't set both 'monitor_region_start' and
'monitor_region_end'.


Thanks,
SJ