From mboxrd@z Thu Jan 1 00:00:00 1970 From: nico@fluxnic.net (Nicolas Pitre) Date: Thu, 16 Sep 2010 13:58:09 -0400 (EDT) Subject: Maximum bootable kernel size in current ARM linux In-Reply-To: <1284657411.32513.3.camel@e102109-lin.cambridge.arm.com> References: <4C8DD588.7040009@endruntechnologies.com> <201009131043.48688.marek.vasut@gmail.com> <20100913101039.GC2614@kw.sim.vm.gnt> <000001cb5409$4726e000$4b4d010a@Emea.Arm.com> <1284468849.933.2.camel@e102109-lin.cambridge.arm.com> <1284657411.32513.3.camel@e102109-lin.cambridge.arm.com> Message-ID: To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Thu, 16 Sep 2010, Catalin Marinas wrote: > On Tue, 2010-09-14 at 13:37 -0400, Nicolas Pitre wrote: > > On Tue, 14 Sep 2010, Catalin Marinas wrote: > > > > > I think the Thumb-2 branch goes up to 16MB range. The Thumb-1 may be > > > smaller but we don't support this in the kernel. That's why Thumb-2 > > > modules are within 8MB below PAGE_OFFSET. But this leaves us with > > > maximum 8MB of kernel size. > > > > Hmmm. Would be worth moving the pkmap area below modules then. > > So currently the pkmap area is at PAGE_OFFSET - 2MB. On a Thumb-2 kernel > with highmem enabled we would have 6MB available to modules. Is this big > enough? If not, we could move the pkmap area. It is probably enough. But it is just not optimal. If the area between TASK_SIZE and PAGE_OFFSET-8M is unused, then it would make sense to move the pkmap area there instead. > BTW, can it be moved in the top part of the memory rather than below > PAGE_OFFSET? It could, but top memory layout tend to be machine specific, or already used by the consistent DMA. And the module area is underused anyway. Nicolas