Messages in this thread | | | From | Michael Nazzareno Trimarchi <> | Date | Mon, 19 Sep 2022 13:59:39 +0200 | Subject | Re: Correlation CMA size and FORCE_MAX_ZONEORDER |
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Hi David
On Mon, Sep 19, 2022 at 1:28 PM David Hildenbrand <david@redhat.com> wrote: > > On 19.09.22 13:17, Michael Nazzareno Trimarchi wrote: > > 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. > > Yes, in an ideal case it should be automatic. > > > 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 > > FORCE_MAX_ZONEORDER is just a way to increase/decrease the maximum > allocation size of the buddy in general. > > > CMA align and can fit inside a region should be allowed > > > > What am I missing? > > I think that the issue is that the CMA alignments nowadays depend on the > pageblock size. And the pageblock size depends on *some* configurations > on the maximum allocation size of the buddy. > > Documenting the interaction between FORCE_MAX_ZONEORDER and CMA size > alignment is not trivial. > > For example, with CONFIG_HUGETLB_PAGE there might not be such an > interaction. With CONFIG_HUGETLB_PAGE, there clearly is one. > > > Let me phrase it this way: is it good enough in you setup to get 32mb vs > 8mb or do you want/need to reduce it without adjusting > FORCE_MAX_ZONEORDER ?
Wait we have: - CMA kconfig alignment that in most config we have not considered natural dma alignment but is put to 1Mb in a lot of embedded - We have CMA_SIZE, CMA_SIZE_PERCENTAGE etc. Those seems that are not effect if ZONEORDER is not reasonable and without HUGETLB_PAGE - etc
Changing MAX_ZONEORDER is ok and yes if you have an IOT device that you know about your CMA allocation, it makes no sense to have it 32MB for a 128Mb device. What I point out is that I need to figure it out because in Kconfig there is no mention of it. Should it be added there?
Michael
> > -- > Thanks, > > David / dhildenb >
-- Michael Nazzareno Trimarchi Co-Founder & Chief Executive Officer M. +39 347 913 2170 michael@amarulasolutions.com __________________________________
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