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Date:   Wed, 03 Mar 2021 23:17:49 +0530
From:   pintu@codeaurora.org
To:     Vlastimil Babka <vbabka@suse.cz>
Cc:     linux-kernel@vger.kernel.org, akpm@linux-foundation.org,
        linux-mm@kvack.org, linux-fsdevel@vger.kernel.org,
        iamjoonsoo.kim@lge.com, sh_def@163.com, mateusznosek0@gmail.com,
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        keescook@chromium.org, mcgrof@kernel.org,
        mgorman@techsingularity.net, pintu.ping@gmail.com
Subject: Re: [PATCH] mm/compaction: remove unused variable
 sysctl_compact_memory
In-Reply-To: <486d7af3-95a3-9701-f0f9-706ff49b99d1@suse.cz>
References: <1614707773-10725-1-git-send-email-pintu@codeaurora.org>
 <486d7af3-95a3-9701-f0f9-706ff49b99d1@suse.cz>
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On 2021-03-03 22:39, Vlastimil Babka wrote:
> On 3/2/21 6:56 PM, Pintu Kumar wrote:
>> The sysctl_compact_memory is mostly unsed in mm/compaction.c
>> It just acts as a place holder for sysctl.
>> 
>> Thus we can remove it from here and move the declaration directly
>> in kernel/sysctl.c itself.
>> This will also eliminate the extern declaration from header file.
>> No functionality is broken or changed this way.
>> 
>> Signed-off-by: Pintu Kumar <pintu@codeaurora.org>
>> Signed-off-by: Pintu Agarwal <pintu.ping@gmail.com>
> 
> You should be able to remove the variable completely and set .data to 
> NULL in
> the corresponding entry. The sysctl_compaction_handler doesn't access 
> it at all.
> 
> Then you could do the same with drop_caches. Currently
> drop_caches_sysctl_handler currently writes to it, but that can be 
> avoided using
> a local variable - see how sysrq_sysctl_handler avoids the global 
> variable and
> its corresponding .data field is NULL.
> 

Oh yes, thank you so much for the reference.
Yes I was looking to do something similar but didn't realize that is 
possible.
I will re-submit the new patch.

And yes, I will try to explore more on drop_caches part as well.

Thanks,
Pintu