Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [PATCH] mm/compaction: remove unused variable
 sysctl_compact_memory
To:     Pintu Kumar <pintu@codeaurora.org>, 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, bhe@redhat.com,
        nigupta@nvidia.com, yzaikin@google.com, keescook@chromium.org,
        mcgrof@kernel.org, mgorman@techsingularity.net
Cc:     pintu.ping@gmail.com
References: <1614707773-10725-1-git-send-email-pintu@codeaurora.org>
From:   Vlastimil Babka <vbabka@suse.cz>
Message-ID: <486d7af3-95a3-9701-f0f9-706ff49b99d1@suse.cz>
Date:   Wed, 3 Mar 2021 18:09:18 +0100
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101
 Thunderbird/78.7.1
MIME-Version: 1.0
In-Reply-To: <1614707773-10725-1-git-send-email-pintu@codeaurora.org>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Precedence: bulk

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.

Vlastimil