linux-kernel - Re: [PATCH v2 6/6] RISC-V: Implement keepinitrd kernel parameter

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Date:   Tue, 12 Feb 2019 10:45:05 -0800
From:   Christoph Hellwig <hch@...radead.org>
To:     Anup Patel <anup@...infault.org>
Cc:     Christoph Hellwig <hch@...radead.org>,
        Palmer Dabbelt <palmer@...ive.com>,
        Anup Patel <Anup.Patel@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Atish Patra <Atish.Patra@....com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>
Subject: Re: [PATCH v2 6/6] RISC-V: Implement keepinitrd kernel parameter

On Tue, Feb 12, 2019 at 03:53:21PM +0530, Anup Patel wrote:
> If it is initramfs (i.e. CPIO image) then contents of CPIO archive
> are extracted to create a ramfs instance.
> 
> If it is initrd (i.e. some filesystem image) then RAM block device
> is created in-place at initrd location. (Please correct me if I am
> wrong about initrd here).

No.  If it is an initrd image we still copy it into the rootfs first,
and then load it into a ram disk.  Take a look at
init/initramfs.c:populate_rootfs() and
init/do_mounts_initrd.c:initrd_load().

> So in case of initrd we might not want to free-up the RAM but
> we can certainly free-up in case of initramfs.

No, in either case we do not need the original initramfs/initrd
memory.  I suspect arm has this as a workaround for some weird
legacy boot issue, but I can't see any reason why we would not want
to free the memory on riscv.