Even though it's common to see the architecture code using both
bootmem and memblock early memory allocators, it's not good for
multiple reasons. First of all, it's redundant to have two
early memory allocator while one would be more than enough from
functionality and stability points of view. Secondly, some new
features introduced in the kernel utilize the methods of the most
modern allocator ignoring the older one. It means the architecture
code must keep the both subsystems up synchronized with information
about memory regions and reservations, which leads to the code
complexity increase, that obviously increases bugs probability.
Finally it's better to keep all the architectures code unified for
better readability and code simplification. All these reasons lead
to one conclusion - arch code should use just one memory allocator,
which is supposed to be memblock as the most modern and already
utilized by the most of the kernel platforms. This patchset is
mostly about it.
One more reason why the MIPS arch code should finally move to
memblock is a BUG somewhere in the initialization process, when
CMA is activated:
[ 0.248762] BUG: Bad page state in process swapper/0 pfn:01f93
[ 0.255415] page:8205b0ac count:0 mapcount:-127 mapping: (null) index:0x1
[ 0.263172] flags: 0x40000000()
[ 0.266723] page dumped because: nonzero mapcount
[ 0.272049] Modules linked in:
[ 0.275511] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.4.88-module #5
[ 0.282900] Stack : 00000000 00000000 80b6dd6a 0000003a 00000000 00000000 80930000 8092bff4
86073a14 80ac88c7 809f21ac 00000000 00000001 80b6998c 00000400 00000000
80a00000 801822e8 80b6dd68 00000000 00000002 00000000 809f8024 86077ccc
80b80000 801e9328 809fcbc0 00000000 00000400 00010000 86077ccc 86073a14
00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
...
[ 0.323148] Call Trace:
[ 0.325935] [<8010e7c4>] show_stack+0x8c/0xa8
[ 0.330859] [<80404814>] dump_stack+0xd4/0x110
[ 0.335879] [<801f0bc0>] bad_page+0xfc/0x14c
[ 0.340710] [<801f0e04>] free_pages_prepare+0x1f4/0x330
[ 0.346632] [<801f36c4>] __free_pages_ok+0x2c/0x104
[ 0.352154] [<80b23a40>] init_cma_reserved_pageblock+0x5c/0x74
[ 0.358761] [<80b29390>] cma_init_reserved_areas+0x1b4/0x240
[ 0.365170] [<8010058c>] do_one_initcall+0xe8/0x27c
[ 0.370697] [<80b14e60>] kernel_init_freeable+0x200/0x2c4
[ 0.376828] [<808faca4>] kernel_init+0x14/0x104
[ 0.381939] [<80107598>] ret_from_kernel_thread+0x14/0x1c
The bugus pfn seems to be the one allocated for bootmem allocator
pages and hasn't been freed before letting the CMA working with its
areas. Anyway the bug is solved by this patchset.
Another reason why this patchset is useful is that it fixes the fdt
reserved-memory nodes functionality for MIPS. Really it's bug to have
the fdt reserved nodes scanning before the memblock is
fully initialized (calling early_init_fdt_scan_reserved_mem before
bootmem_init is called). Additionally no-map flag of the
reserved-memory node hasn't been taking into account. This patchset
fixes all of these.
As you probably remember I already did another attempt to merge a
similar functionality into the kernel. This time the patchset got
to be less complex (14 patches vs 21 last time) and fixes the
platform code like SGI IP27 and Loongson3, which due to being
NUMA introduce its own memory initialization process. Although
I have much doubt in SGI IP27 code operability in the first place,
since it got prom_meminit() method of early memory initialization,
which hasn't been called at any other place in the kernel. It must
have been left there unrenamed after arch/mips/mips-boards/generic
code had been discarded.
Here are the list of folks, who agreed to perform some tests of
the patchset:
Alexander Sverdlin <alexander.sverdlin@xxxxxxxxx> - Octeon2
Matt Redfearn <matt.redfearn@xxxxxxxx> - Loongson3, etc
Joshua Kinard <kumba@xxxxxxxxxx> - IP27
Marcin Nowakowski <marcin.nowakowski@xxxxxxxx>
Thanks to you all in regards and for everybody, who will be involved
in reviewing and testing.
The patchset is applied on top of kernel 4.15-rc8 and can be found
submitted at my repo:
https://github.com/fancer/Linux-kernel-MIPS-memblock-project
Signed-off-by: Serge Semin <fancer.lancer@xxxxxxxxx>
Serge Semin (14):
MIPS: memblock: Add RESERVED_NOMAP memory flag
MIPS: memblock: Surely map BSS kernel memory section
MIPS: memblock: Reserve initrd memory in memblock
MIPS: memblock: Discard bootmem initialization
MIPS: memblock: Add reserved memory regions to memblock
MIPS: memblock: Reserve kdump/crash regions in memblock
MIPS: memblock: Mark present sparsemem sections
MIPS: memblock: Simplify DMA contiguous reservation
MIPS: memblock: Allow memblock regions resize
MIPS: memblock: Perform early low memory test
MIPS: memblock: Print out kernel virtual mem layout
MIPS: memblock: Discard bootmem from Loongson3 code
MIPS: memblock: Discard bootmem from SGI IP27 code
MIPS: memblock: Deactivate bootmem allocator
arch/mips/Kconfig | 2 +-
arch/mips/include/asm/bootinfo.h | 1 +
arch/mips/kernel/prom.c | 8 +-
arch/mips/kernel/setup.c | 218 +++++++++------------
arch/mips/loongson64/loongson-3/numa.c | 16 +-
arch/mips/mm/init.c | 47 +++++
arch/mips/sgi-ip27/ip27-memory.c | 9 +-
7 files changed, 153 insertions(+), 148 deletions(-)
--
2.12.0
