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Date: Thu, 30 Aug 2018 21:19:20 +0800 From: Feng Tang <feng.tang@...el.com> To: Thomas Gleixner <tglx@...utronix.de> Cc: Michal Hocko <mhocko@...nel.org>, Peter Zijlstra <peterz@...radead.org>, linux-kernel@...r.kernel.org, x86@...nel.org, Ingo Molnar <mingo@...e.hu>, "H . Peter Anvin" <hpa@...ux.intel.com>, Yinghai Lu <yinghai@...nel.org>, Dave Hansen <dave.hansen@...el.com>, Andi Kleen <ak@...ux.intel.com> Subject: Re: [PATCH] x86, mm: Reserver some memory for bootmem allocator for NO_BOOTMEM Hi Thomas, On Thu, Aug 30, 2018 at 03:05:31PM +0200, Thomas Gleixner wrote: > On Thu, 30 Aug 2018, Feng Tang wrote: > > On Thu, Aug 30, 2018 at 02:49:15PM +0200, Michal Hocko wrote: > > > On Thu 30-08-18 13:54:19, Thomas Gleixner wrote: > > > > On Thu, 30 Aug 2018, Michal Hocko wrote: > > > > > On Thu 30-08-18 12:44:02, Peter Zijlstra wrote: > > > > > > On Thu, Aug 30, 2018 at 05:03:19PM +0800, Feng Tang wrote: > > > > > > > The root cause is that when CONFIG_NO_BOOTMEM=y, before > > > > > > > e820__memblock_setup() is called there is no memory for bootmem > > > > > > > to allocate, > > > > > > > > > > > > Which you bloody well asked for by using NO_BOOTMEM=y. > > > > > > > > > > > > Going down this route; adding hacks for every little thing that does > > > > > > want bootmem, completely defeats the purpose. > > > > > > > > > > > > If anything, make the earlycon thing depend on NO_BOOTMEM=n. That also > > > > > > solves your problem. No earlycon, no panic. > > > > > > > > > > Well, there is endeavor to remove bootmem allocator altogether. So > > > > > making earlycon depend on NO_BOOTMEM=n doesn't sound like a good fit to > > > > > > > > If we want to remove bootmem, then reintroducing it with a static bootmem > > > > section doesn't make any sense at all. > > > > > > I have actually checked the code now and see what you mean. I thought it > > > would be a single allocation that is needed but that is not the case so > > > the static buffer is not going to fly. > > > > Exactly! I tried several ways for the static allocation, like in data, in bss > > section, but they all failed, as in the very start of setup_arch(): > > > > memblock_reserve(__pa_symbol(_text), > > (unsigned long)__bss_stop - (unsigned long)_text); > > > > Those [_text, __bss_stop] is not able to be used by alloc_bootmem(). And I > > only got this patch, and really appreciate any good suggestions. > > And why do you want to use bootmem in the first place? If boot mem is going > away, why are you not fixing the early console crap to NOT use bootmem at > all? The earlycon need use fixmap to map the mmio register, while fixmap will need a new page for page table if the pmd/pte is not already their, as shown in the commit log: panic+0xd2/0x220 __alloc_bootmem+0x31/0x34 spp_getpage+0x60/0x8a fill_pte+0x71/0x130 __set_pte_vaddr+0x1d/0x50 set_pte_vaddr+0x3c/0x60 __native_set_fixmap+0x23/0x30 native_set_fixmap+0x30/0x40 setup_earlycon+0x1e0/0x32f param_setup_earlycon+0x13/0x22 do_early_param+0x5b/0x90 parse_args+0x1f7/0x300 parse_early_options+0x24/0x28 parse_early_param+0x65/0x73 setup_arch+0x31e/0x9f1 start_kernel+0x58/0x44e inside the spp_getpage(): if (after_bootmem) ptr = (void *) get_zeroed_page(GFP_ATOMIC); else ptr = alloc_bootmem_pages(PAGE_SIZE); Thanks, Feng
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