Messages in this thread Patch in this message | | | Subject | Re: [PATCH 02/14] MIPS: memblock: Surely map BSS kernel memory section | From | Matt Redfearn <> | Date | Wed, 24 Jan 2018 09:49:31 +0000 |
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Hi Serge,
On 23/01/18 19:27, Serge Semin wrote: > Hello Matt, > > On Tue, Jan 23, 2018 at 11:03:27AM +0000, Matt Redfearn <matt.redfearn@mips.com> wrote: >> Hi Serge, >> >> On 22/01/18 21:47, Serge Semin wrote: >>> Hello Matt, >>> >>> On Mon, Jan 22, 2018 at 04:35:26PM +0000, Matt Redfearn <matt.redfearn@mips.com> wrote: >>>> Hi Serge, >>>> >>>> On 17/01/18 22:23, Serge Semin wrote: >>>>> The current MIPS code makes sure the kernel code/data/init >>>>> sections are in the maps, but BSS should also be there. >>>> >>>> Quite right - it should. But this was protected against by reserving all >>>> bootmem up to the _end symbol here: >>>> http://elixir.free-electrons.com/linux/v4.15-rc8/source/arch/mips/kernel/setup.c#L388 >>>> Which you remove in the next patch in this series. I'm not sure it is worth >>> >>> Right. Missed that part. The old code just doesn't set the kernel memory free >>> calling the free_bootmem() method for non-reserved parts below reserved_end. >>> >>>> disentangling the reserved_end stuff from the next patch to make this into a >>>> single logical change of reserving just .bss rather than everything below >>>> _end. >>> >>> Good point. I'll move this change into the "[PATCH 05/14] MIPS: memblock: >>> Add reserved memory regions to memblock". It logically belongs to that place. >>> Since basically by the arch_mem_addpart() calls we reserve all the kernel >> >> >> Actually I was wrong - it's not this sequence of arch_mem_addpart's that >> reserves the kernels memory. At least on DT based systems, it's pretty >> likely that these regions will overlap with the system memory already added. >> of_scan_flat_dt will look for the memory node and add it via >> early_init_dt_add_memory_arch. >> These calls to add the kernel text, init and bss detect that they overlap >> with the already present system memory, so don't get added, here: >> http://elixir.free-electrons.com/linux/v4.15-rc9/source/arch/mips/kernel/setup.c#L759 >> >> As such, when we print out the content of boot_mem_map, we only have a >> single entry: >> >> [ 0.000000] Determined physical RAM map: >> [ 0.000000] memory: 10000000 @ 00000000 (usable) >> >> >>> memory now I'd also merged them into a single call for the range [_text, _end]. >>> What do you think? >> >> >> I think that this patch makes sense in case the .bss is for some reason not >> covered by an existing entry, but I would leave it as a separate patch. >> >> Your [PATCH 05/14] MIPS: memblock: Add reserved memory regions to memblock >> is actually self-contained since it replaces reserving all memory up to _end >> with the single reservation of the kernel's whole size >> >> + size = __pa_symbol(&_end) - __pa_symbol(&_text); >> + memblock_reserve(__pa_symbol(&_text), size); >> >> >> Which I think is definitely an improvement since it is much clearer. >> > > Alright lets sum it up. First of all, yeah, you are right, arch_mem_addpart() > is created to make sure the kernel memory is added to the memblock/bootmem pool. > The previous arch code was leaving such the memory range non-freed since it was > higher the reserved_end, so to make sure the early memory allocations wouldn't > be made from the pages, where kernel actually resides. > > In my code I still wanted to make sure the kernel memory is in the memblock pool. > But I also noticed, that .bss memory range wouldn't be added to the pool if neither > dts nor platform-specific code added any memory to the boot_mem_map pool. So I > decided to fix it. The actual kernel memory reservation is performed after all > the memory regions are declared by the code you cited. It's essential to do > the [_text, _end] memory range reservation there, otherwise memblock may > allocate from the memory range occupied by the kernel code/data. > > Since you agree with leaving it in the separate patch, I'd only suggest to > call the arch_mem_addpart() method for just one range [_text, _end] instead of > doing it three times for a separate _text, _data and bss sections. What do you > think?
I think it's best left as 3 separate reservations, mainly due to the different attribute used for the init section. So all in all, I like this patch as it is.
Thanks, Matt
> > Regards, > -Sergey > >> Thanks, >> Matt >> >>> >>> Regards, >>> -Sergey >>> >>>> >>>> Reviewed-by: Matt Redfearn <matt.redfearn@mips.com> >>>> >>>> Thanks, >>>> Matt >>>> >>>>> >>>>> Signed-off-by: Serge Semin <fancer.lancer@gmail.com> >>>>> --- >>>>> arch/mips/kernel/setup.c | 3 +++ >>>>> 1 file changed, 3 insertions(+) >>>>> >>>>> diff --git a/arch/mips/kernel/setup.c b/arch/mips/kernel/setup.c >>>>> index 76e9e2075..0d21c9e04 100644 >>>>> --- a/arch/mips/kernel/setup.c >>>>> +++ b/arch/mips/kernel/setup.c >>>>> @@ -845,6 +845,9 @@ static void __init arch_mem_init(char **cmdline_p) >>>>> arch_mem_addpart(PFN_UP(__pa_symbol(&__init_begin)) << PAGE_SHIFT, >>>>> PFN_DOWN(__pa_symbol(&__init_end)) << PAGE_SHIFT, >>>>> BOOT_MEM_INIT_RAM); >>>>> + arch_mem_addpart(PFN_DOWN(__pa_symbol(&__bss_start)) << PAGE_SHIFT, >>>>> + PFN_UP(__pa_symbol(&__bss_stop)) << PAGE_SHIFT, >>>>> + BOOT_MEM_RAM); >>>>> pr_info("Determined physical RAM map:\n"); >>>>> print_memory_map(); >>>>>
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