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SubjectRe: [PATCH] use initmpfs even if there's root= cmdline

On 12/12/13 20:38, Dave Young wrote:
> On 12/12/13 at 05:25pm, Dave Young wrote:
>> Current code use ramfs instead of tmpfs for stub when root= defined.
>> But for real use case with initramfs, usually there's like cmdline like
>> root=UUID=$UUID the root dev is the real device. For that case we have
>> no way to use initmpfs, thus this patch removes the limitation so tmpfs
>> can benefit more people.

The reason I did that was if you specify a root= then you don't want to
_stay_ on rootfs. You specify root= so either the kernel does
switch_root for you, or so rootfs does a swich_root at the end.

The point of initmpfs is that when rootfs _is_ the "real" root device,
it can benefit from being tmpfs. When you're just goign to switch to a
different root device, tmpfs doesn't make much difference.

> Discussed with Vivek Goyal about the kdump use case, I missed one thing that
> tmpfs has default size limit though we can tune it.
> So I will think more about it, will address this later, please ignore this
> patch.

I have a vague todo item of feeding rootflags= through to initmpfs, but
that's really intended to specify flags for root=. There isn't really an
existing command line option to specify initramfs flags because ramfs
doesn't care.

It was one of those "only parse rootflags= for initmpfs when there's no
root=" vs "create a new rdrootflags= ala rdinit= even though that's a
subtly wrong name these days..." and it went on the todo list because
neither approach was obviously superior.

Happy to take suggestions and whip up a patch if this is inconveniencing
somebody. :)

> Thanks
> Dave


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