Messages in this thread | | | Date | Wed, 8 Jun 2022 15:27:09 +0800 | Subject | Re: [PATCH v3 5/6] mm: Add mirror flag back on initrd memory | From | mawupeng <> |
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在 2022/6/7 22:49, Ard Biesheuvel 写道: > On Tue, 7 Jun 2022 at 14:22, David Hildenbrand <david@redhat.com> wrote: >> >> On 07.06.22 11:38, Wupeng Ma wrote: >>> From: Ma Wupeng <mawupeng1@huawei.com> >>> >>> Initrd memory will be removed and then added in arm64_memblock_init() and this >>> will cause it to lose all of its memblock flags. The lost of MEMBLOCK_MIRROR >>> flag will lead to error log printed by find_zone_movable_pfns_for_nodes if >>> the lower 4G range has some non-mirrored memory. >>> >>> In order to solve this problem, the lost MEMBLOCK_MIRROR flag will be >>> reinstalled if the origin memblock has this flag. >>> >>> Signed-off-by: Ma Wupeng <mawupeng1@huawei.com> >>> --- >>> arch/arm64/mm/init.c | 9 +++++++++ >>> include/linux/memblock.h | 1 + >>> mm/memblock.c | 20 ++++++++++++++++++++ >>> 3 files changed, 30 insertions(+) >>> >>> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c >>> index 339ee84e5a61..11641f924d08 100644 >>> --- a/arch/arm64/mm/init.c >>> +++ b/arch/arm64/mm/init.c >>> @@ -350,9 +350,18 @@ void __init arm64_memblock_init(void) >>> "initrd not fully accessible via the linear mapping -- please check your bootloader ...\n")) { >>> phys_initrd_size = 0; >>> } else { >>> + int flags, ret; >>> + >>> + ret = memblock_get_flags(base, &flags); >>> + if (ret) >>> + flags = 0; >>> + >>> memblock_remove(base, size); /* clear MEMBLOCK_ flags */ >>> memblock_add(base, size); >>> memblock_reserve(base, size); >> >> Can you explain why we're removing+re-adding here exactly? Is it just to >> clear flags as the comment indicates? >> > > This should only happen if the placement of the initrd conflicts with > a mem= command line parameter or it is not covered by memblock for > some other reason. > > IOW, this should never happen, and if re-memblock_add'ing this memory > unconditionally is causing problems, we should fix that instead of > working around it.
This will happen if we use initrdmem=3G,100M to reserve initrd memory below the 4G limit to test this scenario(just for testing, I have trouble to boot qemu with initrd enabled and memory below 4G are all mirror memory).
Re-memblock_add'ing this memory unconditionally seems fine but clear all flags(especially MEMBLOCK_MIRROR) may lead to some error log.
> >> If it's really just about clearing flags, I wonder if we rather want to >> have an interface that does exactly that, and hides the way this is >> actually implemented (obtain flags, remove, re-add ...), internally. >> >> But most probably there is more magic in the code and clearing flags >> isn't all it ends up doing. >> > > I don't remember exactly why we needed to clear the flags, but I think > it had to do with some corner case we hit when the initrd was > partially covered. If "mem=" is set in command line, memblock_mem_limit_remove_map() will remove all memory block without MEMBLOCK_NOMAP. Maybe this will bring the memory back if this initrd mem has the MEMBLOCK_NOMAP flag?
The rfc version [1] introduce and use memblock_clear_nomap() to clear the MEMBLOCK_NOMAP of this initrd memblock. So maybe the usage of memblock_remove() is just to avoid introducing new function(memblock_clear_nomap)?
Since commit 4c546b8a3469 ("memblock: add memblock_clear_nomap()") already introduced memblock_clear_nomap(). Can we use this to remove flag MEMBLOCK_NOMAP to solve this problem rather than bring flag MEMBLOCK_MIRROR back?
[1] https://lore.kernel.org/linux-arm-kernel/20160202180622.GP10166@arm.com/T/#t > .
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