linux-kernel - Re: [PATCH 3/4] ARM: change vmalloc_min to vmalloc

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Message-ID: <CACRpkdbZObW2SXdTUkPrsezjjVU19emts420EN-uhkHWb+4vrA@mail.gmail.com>
Date:   Wed, 19 May 2021 00:19:58 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     "Russell King (Oracle)" <rmk+kernel@...linux.org.uk>,
        Nicolas Pitre <nico@...xnic.net>
Cc:     Yanfei Xu <yanfei.xu@...driver.com>,
        Mike Rapoport <rppt@...nel.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Hailong liu <carver4lio@....com>,
        Tian Tao <tiantao6@...ilicon.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/4] ARM: change vmalloc_min to vmalloc_start

On Tue, May 18, 2021 at 2:15 PM Russell King (Oracle)
<rmk+kernel@...linux.org.uk> wrote:

> Change the current vmalloc_min, which is supposed to be the lowest
> address of vmalloc space including the VMALLOC_OFFSET, to vmalloc_start
> which does not include VMALLOC_OFFSET.
>
> Signed-off-by: Russell King (Oracle) <rmk+kernel@...linux.org.uk>

Reviewed-by: Linus Walleij <linus.walleij@...aro.org>

> +static unsigned long __initdata vmalloc_start = VMALLOC_END - (240 << 20);

When I first read this it took me some time to figure out what was
going on here, so if you have time, please fold in a comment
with some explanation of that (240 << 20) thing, in some blog
post I described it as "an interesting way to write 0x0f000000"
but I suppose commit 0536bdf33faf chose this way for a
specific reason? (Paging Nico if he can explain it.)

Yours,
Linus Walleij