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SubjectRe: Correlation CMA size and FORCE_MAX_ZONEORDER
Hi

On Mon, Sep 19, 2022 at 11:31 AM David Hildenbrand <david@redhat.com> wrote:
>
> On 19.09.22 11:17, Michael Nazzareno Trimarchi wrote:
> > Hi David
> >
> > On Mon, Sep 19, 2022 at 10:38 AM David Hildenbrand <david@redhat.com> wrote:
> >>
> >> On 15.09.22 23:36, Michael Nazzareno Trimarchi wrote:
> >>> Hi all
> >>
> >> Hi,
> >>
> >>>
> >>> Working on a small device with 128MB of memory and using imx_v6_v7
> >>> defconfig I found that CMA_SIZE_MBYTES, CMA_SIZE_PERCENTAGE
> >>> are not respected. The calculation done does not allow the requested
> >>> size. I think that this should be somehow documented and described but
> >>> I did not
> >>> find the documentation. Does it work this way?
> >>>
> >>> With CMA_SIZE of 8MB I need to have FORCE_MAX_ZONEORDER=12 if I have
> >>> the default FORCE_MAX_ZONEORDER=14 the min size is 32Mb
> >>
> >> The underlying constraint is that CMA regions require a certain minimum
> >> alignment+size. They cannot be arbitrarily in size.
> >>
> >> CMA_MIN_ALIGNMENT_BYTES expresses that, and corresponds in upstream
> >> kernels to the size of a single pageblock.
> >>
> >> In previous kernels, it used to be the size of the largest buddy
> >> allocation granularity (derived from MAX_ORDER, derived from
> >> FORCE_MAX_ZONEORDER).
> >>
> >> On upstream kernels, the FORCE_MAX_ZONEORDER constraint should no longer
> >> apply. On most archs, the minimum alignment+size should be 2 MiB
> >> (x86-64, aarch64 with 4k base pages) -- the size of a single pageblock.
> >>
> >> So far the theory. Are you still running into this limitation on
> >> upstream kernels?
> >>
> >
> > I can run 6-rc2 on my board. I test again but according to it, if I
> > put 4M as CMA in cma=4M in boot
> > parameters, the result is 32Mb of CMA. Apart of that seems that
> > process lime tiny membench can not even start
> > to mblock memory
> >
>
> The CMA alignemnt change went into v5.19. If "cma=4M" still gives you >
> 4M, can you post /proc/meminfo and the early console output?
>

cat /proc/cmdline
cma=4M mtdparts=gpmi-nand:4m(nandboot),1m(env),24m(kernel),1m(nanddtb),-(rootfs)
root=ubi0:root rw ubi.mtd=ro
otfs rootfstype=ubifs rootwait=1
# cat /proc/meminfo
MemTotal: 109560 kB
MemFree: 56084 kB
MemAvailable: 56820 kB
Buffers: 0 kB
Cached: 39680 kB
SwapCached: 0 kB
Active: 44 kB
Inactive: 644 kB
Active(anon): 44 kB
Inactive(anon): 644 kB
Active(file): 0 kB
Inactive(file): 0 kB
Unevictable: 39596 kB
Mlocked: 0 kB
HighTotal: 0 kB
HighFree: 0 kB
LowTotal: 109560 kB
LowFree: 56084 kB
SwapTotal: 0 kB
SwapFree: 0 kB
Dirty: 0 kB
Writeback: 0 kB
AnonPages: 628 kB
Mapped: 1480 kB
Shmem: 84 kB
KReclaimable: 4268 kB
Slab: 8456 kB
SReclaimable: 4268 kB
SUnreclaim: 4188 kB
KernelStack: 392 kB
PageTables: 88 kB
NFS_Unstable: 0 kB
Bounce: 0 kB
WritebackTmp: 0 kB
CommitLimit: 54780 kB
Committed_AS: 1876 kB
VmallocTotal: 901120 kB
VmallocUsed: 2776 kB
VmallocChunk: 0 kB
Percpu: 72 kB
CmaTotal: 32768 kB
CmaFree: 32484 kB
# uname -a
Linux buildroot 6.0.0-rc5 #20 SMP Mon Sep 19 11:51:26 CEST 2022 armv7l GNU/Linux
#

Then here https://pastebin.com/6MUB2VBM dmesg

CONFIG_ARM_MODULE_PLTS=y
CONFIG_FORCE_MAX_ZONEORDER=14
CONFIG_ALIGNMENT_TRAP=y
...
CONFIG_CMA
CONFIG_CMA_AREAS=7
...

CONFIG_CMA_SIZE_MBYTES=8
CONFIG_CMA_SIZE_SEL_MBYTES=y

Michael

>
> --
> Thanks,
>
> David / dhildenb
>
--
Michael Nazzareno Trimarchi
Co-Founder & Chief Executive Officer
M. +39 347 913 2170
michael@amarulasolutions.com
__________________________________

Amarula Solutions BV
Joop Geesinkweg 125, 1114 AB, Amsterdam, NL
T. +31 (0)85 111 9172
info@amarulasolutions.com
www.amarulasolutions.com

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