Messages in this thread | | | From | Michael Nazzareno Trimarchi <> | Date | Mon, 19 Sep 2022 11:17:53 +0200 | Subject | Re: Correlation CMA size and FORCE_MAX_ZONEORDER |
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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
Michael
> -- > Thanks, > > David / dhildenb >
-- Michael Nazzareno Trimarchi Co-Founder & Chief Executive Officer M. +39 347 913 2170 michael@amarulasolutions.com __________________________________
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