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41555cc9e2
on an arch level, RISC-V defaults to FLATMEM. On PolarFire SoC, the memory layout is almost always sparse, with a maximum of 1 GiB at 0x8000_0000 & a possible 16 GiB range at 0x10_0000_0000. The Icicle kit, for example, has 2 GiB of DDR - so there's a big hole in the memory map between the two gigs. Prior to v6.1-rc1, boot times from defconfig builds were pretty bad on Icicle but enabling sparsemem would fix those issues. As of v6.1-rc1, the Icicle kit no longer boots from defconfig builds with the in-kernel devicetree. A change to the memory map resulted in a futher "sparse-ification", producing a splat on boot: OF: fdt: Ignoring memory range 0x80000000 - 0x80200000 Machine model: Microchip PolarFire-SoC Icicle Kit earlycon: ns16550a0 at MMIO32 0x0000000020100000 (options '115200n8') printk: bootconsole [ns16550a0] enabled printk: debug: skip boot console de-registration. efi: UEFI not found. Zone ranges: DMA32 [mem 0x0000000080200000-0x00000000ffffffff] Normal [mem 0x0000000100000000-0x000000107fffffff] Movable zone start for each node Early memory node ranges node 0: [mem 0x0000000080200000-0x00000000bfbfffff] node 0: [mem 0x00000000bfc00000-0x00000000bfffffff] node 0: [mem 0x0000001040000000-0x000000107fffffff] Initmem setup node 0 [mem 0x0000000080200000-0x000000107fffffff] Kernel panic - not syncing: Failed to allocate 1073741824 bytes for node 0 memory map CPU: 0 PID: 0 Comm: swapper Not tainted 5.19.0-dirty #1 Hardware name: Microchip PolarFire-SoC Icicle Kit (DT) Call Trace: [<ffffffff800057f0>] show_stack+0x30/0x3c [<ffffffff807d5802>] dump_stack_lvl+0x4a/0x66 [<ffffffff807d5836>] dump_stack+0x18/0x20 [<ffffffff807d1ae8>] panic+0x124/0x2c6 [<ffffffff80814064>] free_area_init_core+0x0/0x11e [<ffffffff80813720>] free_area_init_node+0xc2/0xf6 [<ffffffff8081331e>] free_area_init+0x222/0x260 [<ffffffff808064d6>] misc_mem_init+0x62/0x9a [<ffffffff80803cb2>] setup_arch+0xb0/0xea [<ffffffff8080039a>] start_kernel+0x88/0x4ee ---[ end Kernel panic - not syncing: Failed to allocate 1073741824 bytes for node 0 memory map ]--- With the aim of keeping defconfig builds booting on icicle, enable SPARSEMEM_MANUAL. Signed-off-by: Conor Dooley <conor.dooley@microchip.com> Link: https://lore.kernel.org/r/20221021160028.4042304-1-conor@kernel.org Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
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.