Messages in this thread | | | From | Michael Nazzareno Trimarchi <> | Date | Mon, 19 Sep 2022 13:17:45 +0200 | Subject | Re: Correlation CMA size and FORCE_MAX_ZONEORDER |
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Hi
On Mon, Sep 19, 2022 at 1:03 PM David Hildenbrand <david@redhat.com> wrote: > > On 19.09.22 11:57, Michael Nazzareno Trimarchi wrote: > > 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 > > > > Thanks! > > I assume that in your setup, the pageblock size depends on MAX_ORDER > and, therefore, FORCE_MAX_ZONEORDER. > > This should be the case especially if CONFIG_HUGETLB_PAGE is not defined > (include/linux/pageblock-flags.h). > > In contrast to what I remember, the pageblock size does not seem to > depend on the THP size (weird) as well. > > > So, yes, that limitation is still in effect for some kernel configs. > > One could make the pageblock size configurable (similar to > CONFIG_HUGETLB_PAGE_SIZE_VARIABLE) or simply default to a smaller > pageblock size as default with CONFIG_CMA and !CONFIG_HUGETLB_PAGE. > > I imagine something reasonable might be to set the pageblock size to > 2MiB without CONFIG_HUGETLB_PAGE but with CONFIG_CMA. >
I don't think making more configuration options makes things clear. When we enable some configuration we can force down the configuration. You need to explain clearly how you envision it. FORCE_MAX_ZONEORDER for me is the largest allocation that you can get from a zone (ex CMA one). Any request allocation that is align to the CMA align and can fit inside a region should be allowed
What am I missing?
Michael
> -- > Thanks, > > David / dhildenb > -- Michael Nazzareno Trimarchi Co-Founder & Chief Executive Officer M. +39 347 913 2170 michael@amarulasolutions.com __________________________________
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