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Date: Thu, 30 Aug 2018 21:55:36 +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 On Thu, Aug 30, 2018 at 03:25:42PM +0200, Thomas Gleixner wrote: > On Thu, 30 Aug 2018, Feng Tang wrote: > > On Thu, Aug 30, 2018 at 03:05:31PM +0200, Thomas Gleixner wrote: > > > > 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); > > And where is the problem? We know that we need the fixmap during early boot > anyway, so allocating the PTE page statically and setting it up early > enough is not really rocket science. No allocator required. Yes, if the bootmem itslef is going way, setting up the page table for fixmap is a cleaner solution. Thanks, Feng
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