Hello Matt, On Tue, Jan 23, 2018 at 11:03:27AM +0000, Matt Redfearn <matt.redfearn@xxxxxxxx> 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@xxxxxxxx> 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? Regards, -Sergey > Thanks, > Matt > > > > >Regards, > >-Sergey > > > >> > >>Reviewed-by: Matt Redfearn <matt.redfearn@xxxxxxxx> > >> > >>Thanks, > >>Matt > >> > >>> > >>>Signed-off-by: Serge Semin <fancer.lancer@xxxxxxxxx> > >>>--- > >>> 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(); > >>>
