James, On Fri, Sep 16, 2016 at 05:04:34PM +0100, James Morse wrote: > (Cc: Ard), > > Mark, Ard, how does/will reserved-memory work on an APCI only system? > > > On 07/09/16 05:29, AKASHI Takahiro wrote: > > v26-specific note: After a comment from Rob[0], an idea of adding > > "linux,usable-memory-range" was dropped. Instead, an existing > > "reserved-memory" node will be used to limit usable memory ranges > > on crash dump kernel. > > This works not only on UEFI/ACPI systems but also on DT-only systems, > > but if he really insists on using DT-specific "usable-memory" property, > > I will post additional patches for kexec-tools. Those would be > > redundant, though. > > Even in that case, the kernel will not have to be changed. > > Some narrative on how the old memory ranges get reserved, as there is no longer > any code in the series doing this, (which is pretty neat!): Thank you for detailed explanation :) I was wondering whether I should have added such kind of description, but it was nothing but, I believed, a "normal" DT behavior. > kexec-tools parses the list of memory ranges in /proc/iomem, and adds a node to > the /reserved-memory for System RAM ranges that don't cover the crash kernel. > Decompiling the crash-kernel DT from Seattle, it looks roughly like this: > > reserved-memory { > ranges; > #size-cells = <0x2>; > #address-cells = <0x2>; > > crash_dump at 83ffe50000 { > no-map; > reg = <0x83 0xffe50000 0x0 0x1b0000>; > }; > > [ ... ] > }; > > > 'no-map' means its doing the same thing to memblock as > 'linux,usable-memory-range' did in earlier versions, > early_init_dt_reserve_memory_arch() takes no-map to mean memblock_remove(). > We trigger the removing via early_init_fdt_scan_reserved_mem() in > arch/arm64/mm/init.c. This happens later than before, but its before the > crashkernel and cma ranges get reserved. > > One difference I can see is that before we avoided memblock_remove()ing ranges > that were also in memblock.nomap. This was to avoid the ACPI tables getting > mapped as device memory by mistake, this is fixed by [1]. Now these ranges are > published in /proc/iomem as 'reserved' and won't get covered by a > reserved-memory node, and so we don't need to check memblock.nomap when > memblock_remove()ing. > > > The only odd thing I can see is for a (mythical?) pure-ACPI system. The EFI stub > will create a DT with a chosen node containing pointers to the memory map and > the efi command line. Now such as system may also grow a /reserved-memory node > after kdump. I don't think this is a problem, but it may not match how an > acpi-only system reserves memory. (how does that work?) I didn't get what you mean by "may grow a /reserved-memory after kdump." > > > [1] "arm64: mark reserved memblock regions explicitly in iomem" > > http://lists.infradead.org/pipermail/linux-arm-kernel/2016-August/450433.html > > This is queued in Will's arm64/for-next/core, > > > [2] "efi: arm64: treat regions with WT/WC set but WB cleared as memory" > > http://lists.infradead.org/pipermail/linux-arm-kernel/2016-August/451491.html > > This is queued in tip, but I can't see why kdump depends on it. It only has an > effect if the uefi memory map has !WB regions that linux needs to use. Just because you said that the patch had fixed your problem on Seattle. If I misunderstood, it will be fine to remove this reference from my commit message. Thanks, -Takahiro AKASHI > > Thanks, > > James >