Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Tue, 12 Mar 2019 17:44:22 +0100
From:   Michal Hocko <mhocko@kernel.org>
To:     Yafang Shao <laoar.shao@gmail.com>
Cc:     Vlastimil Babka <vbabka@suse.cz>,
        Souptick Joarder <jrdr.linux@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linux MM <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>, shaoyafang@didiglobal.com
Subject: Re: [PATCH] mm: compaction: some tracepoints should be defined only
 when CONFIG_COMPACTION is set
Message-ID: <20190312164422.GD5721@dhcp22.suse.cz>
References: <1551501538-4092-1-git-send-email-laoar.shao@gmail.com>
 <1551501538-4092-2-git-send-email-laoar.shao@gmail.com>
 <20190312161803.GC5721@dhcp22.suse.cz>
 <CALOAHbBR119mzbkkQ5fmGQ5Bqxu2O4EFgq89gVRXqXN+USzDEA@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CALOAHbBR119mzbkkQ5fmGQ5Bqxu2O4EFgq89gVRXqXN+USzDEA@mail.gmail.com>
User-Agent: Mutt/1.10.1 (2018-07-13)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Wed 13-03-19 00:29:57, Yafang Shao wrote:
> On Wed, Mar 13, 2019 at 12:18 AM Michal Hocko <mhocko@kernel.org> wrote:
> >
> > On Sat 02-03-19 12:38:58, Yafang Shao wrote:
> > > Only mm_compaction_isolate_{free, migrate}pages may be used when
> > > CONFIG_COMPACTION is not set.
> > > All others are used only when CONFIG_COMPACTION is set.
> >
> > Why is this an improvement?
> >
> 
> After this change, if CONFIG_COMPACTION is not set, the tracepoints
> that only work when CONFIG_COMPACTION is set will not be exposed to
> the usespace.
> Without this change, they will always be expose in debugfs no matter
> CONFIG_COMPACTION is set or not.

And this is exactly something that the changelog should mention. I
wasn't aware that we do export tracepoints even when they are not used
by any code path. This whole macro based programming is just a black
magic.
-- 
Michal Hocko
SUSE Labs