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;
MIME-Version: 1.0
References: <20190708170631.2130-1-lpf.vector@gmail.com> <20190708173534.GF32320@bombadil.infradead.org>
In-Reply-To: <20190708173534.GF32320@bombadil.infradead.org>
From:   Pengfei Li <lpf.vector@gmail.com>
Date:   Tue, 9 Jul 2019 01:57:59 +0800
Message-ID: <CAD7_sbEog0OQ+Bxg1nNt2CWgHHLqf602dzhAHTAThPjwK3yitQ@mail.gmail.com>
Subject: Re: [PATCH] mm/vmalloc.c: Remove always-true conditional in vmap_init_free_space
To:     Matthew Wilcox <willy@infradead.org>
Cc:     akpm@linux-foundation.org, Uladzislau Rezki <urezki@gmail.com>,
        rpenyaev@suse.de, peterz@infradead.org, guro@fb.com,
        rick.p.edgecombe@intel.com, rppt@linux.ibm.com,
        aryabinin@virtuozzo.com, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Tue, Jul 9, 2019 at 1:35 AM Matthew Wilcox <willy@infradead.org> wrote:
>
> On Tue, Jul 09, 2019 at 01:06:31AM +0800, Pengfei Li wrote:
> > When unsigned long variables are subtracted from one another,
> > the result is always non-negative.
> >
> > The vmap_area_list is sorted by address.
> >
> > So the following two conditions are always true.
> >
> > 1) if (busy->va_start - vmap_start > 0)
> > 2) if (vmap_end - vmap_start > 0)
> >
> > Just remove them.
>
> That condition won't be true if busy->va_start == vmap_start.

Yes, you're right.
Sorry for my bad job.