Re: [PATCH v4 0/2] mm/highmem: make kmap cache coloring aware
From: Joshua Kinard
Date: Mon Aug 25 2014 - 22:41:16 EST
On 08/25/2014 20:36, David Daney wrote:
> On 08/25/2014 04:55 PM, Joshua Kinard wrote:
>> On 08/25/2014 13:16, Ralf Baechle wrote:
>>> On Sat, Aug 02, 2014 at 05:11:37AM +0400, Max Filippov wrote:
>>>> this series adds mapping color control to the generic kmap code, allowing
>>>> architectures with aliasing VIPT cache to use high memory. There's also
>>>> use example of this new interface by xtensa.
>>> I haven't actually ported this to MIPS but it certainly appears to be
>>> the right framework to get highmem aliases handled on MIPS, too.
>>> Though I still consider increasing PAGE_SIZE to 16k the preferable
>>> solution because it will entirly do away with cache aliases.
>> Won't setting PAGE_SIZE to 16k break some existing userlands (o32)? I use a
>> 4k PAGE_SIZE because the last few times I've tried 16k or 64k, init won't
>> load (SIGSEGVs or such, which panicks the kernel).
> It isn't supposed to break things. Using "stock" toolchains should result
> in executables that will run with any page size.
> In the past, some geniuses came up with some linker (ld) patches that, in
> order to save a few KB of RAM, produced executables that ran only on 4K pages.
> There were some equally astute Debian emacs package maintainers that were
> carrying emacs patches into Debian that would not work on non-4K page size
> That said, I think such thinking should be punished. The punishment should
> be to not have their software run when we select non-4K page sizes. The
> vast majority of prepackaged software runs just fine with a larger page size.
Well, it does appear to mostly work now w/ 16k PAGE_SIZE. The Octane booted
into userland with just a couple of "illegal instruction" errors from 'rm'
and 'mdadm'. I wonder if that's tied to a hardcoded PAGE_SIZE somewhere.
Have to dig around and find something that reproduces the problem on demand.
"The past tempts us, the present confuses us, the future frightens us. And
our lives slip away, moment by moment, lost in that vast, terrible in-between."
--Emperor Turhan, Centauri Republic
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