flatmem broken for nommu? [Was: Re: does non-continuous RAM means I need to select the sparse memory model?]

[Uwe Kleine-König]

Hello Stefan,

On Thu, Dec 01, 2011 at 05:10:23PM +0100, Stefan Hellermann wrote:
> Am 01.12.2011 16:39, schrieb Uwe Kleine-König:
> > The problem is that the memory for mem_map is allocated using:
> > 
> > 	map = alloc_bootmem_node_nopanic(pgdat, size);
> > 
> > without any error checking. The _nopanic was introduced by commit
> > 
> > 	8f389a99 (mm: use alloc_bootmem_node_nopanic() on really needed path)
> > 
> > I don't understand the commit's log and don't really see why it should
> > be allowed to not panic if the allocation failes here but use a NULL
> > pointer instead.
> > I put the people involved in 8f389a99 on Cc, maybe someone can comment?
> > 
> > Apart from that it seems I cannot use flatmem as is on my machine. It
> > has only 128kiB at 0x10000000 + 1MiB at 0x80000000 and needs 14MiB to hold the
> > table of "struct page"s. :-(
> > 
> > Best regards
> > Uwe
> > 
> The commit was made after an bug report from me. I have an old x86
> tablet pc with only 8Mb Ram. This machine fails early on bootup without
> this commit. I found an archived message of the bug report here:
> http://comments.gmane.org/gmane.linux.kernel/1135909
I saw that, too, but still I think that at least the last hunk in this
patch is wrong. (I didn't check the others.) For me the allocation for
mem_map failed and instead of handling the error somehow (be it a panic
or not) just using NULL isn't nice.

Best regards
Uwe

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Pengutronix e.K.                           | Uwe Kleine-König            |
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