mirror of
https://github.com/hardkernel/linux.git
synced 2026-06-01 00:36:40 +09:00
21a0e8c14b
On 64-bit book3s, with the hash MMU, we currently define the kernel virtual space (vmalloc, ioremap etc.), to be 16T in size. This is a leftover from pre v3.7 when our user VM was also 16T. Of that 16T we split it 50/50, with half used for PCI IO and ioremap and the other 8T for vmalloc. We never bothered to make it any bigger because 8T of vmalloc ought to be enough for anybody. But it turns out that's not true, the per cpu allocator wants large amounts of vmalloc space, not to make large allocations, but to allow a large stride between allocations, because we use pcpu_embed_first_chunk(). With a bit of juggling we can increase the entire kernel virtual space to 64T. The only real complication is the check of the address in the SLB miss handler, see the comment in the code. Although we could continue to split virtual space 50/50 as we do now, no one seems to be running out of PCI IO or ioremap space. So instead keep that as 8T, and use the remaining 56T for vmalloc. In future we should be able to increase the kernel virtual space to 512T, the code already supports that, it just needs testing on older hardware. Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.