linux-kernel - Re: [PATCH] mm/vmalloc.c: Remove always-true conditional in vmap_init_free

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Date:   Tue, 9 Jul 2019 01:57:59 +0800
From:   Pengfei Li <lpf.vector@...il.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     akpm@...ux-foundation.org, Uladzislau Rezki <urezki@...il.com>,
        rpenyaev@...e.de, peterz@...radead.org, guro@...com,
        rick.p.edgecombe@...el.com, rppt@...ux.ibm.com,
        aryabinin@...tuozzo.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/vmalloc.c: Remove always-true conditional in vmap_init_free_space

On Tue, Jul 9, 2019 at 1:35 AM Matthew Wilcox <willy@...radead.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.