From mboxrd@z Thu Jan 1 00:00:00 1970 From: zhichang.yuan@linaro.org (zhichang.yuan) Date: Sat, 29 Nov 2014 10:20:55 +0800 Subject: [PATCH] arm64:mm: free the useless initial page table In-Reply-To: <20141127122627.GH11511@e104818-lin.cambridge.arm.com> References: <1416558460-7257-1-git-send-email-zhichang.yuan@linaro.org> <20141124143208.GE15872@e104818-lin.cambridge.arm.com> <5474951F.8050809@linaro.org> <20141127122627.GH11511@e104818-lin.cambridge.arm.com> Message-ID: <54792D87.8080809@linaro.org> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 2014?11?27? 20:26, Catalin Marinas wrote: > On Tue, Nov 25, 2014 at 02:41:35PM +0000, zhichang.yuan wrote: >> On 2014?11?24? 22:32, Catalin Marinas wrote: >>> On Fri, Nov 21, 2014 at 08:27:40AM +0000, zhichang.yuan at linaro.org wrote: >>>> From: "zhichang.yuan" >>>> >>>> For 64K page system, after mapping a PMD section, the corresponding initial >>>> page table is not needed any more. That page can be freed. >>>> >>>> Signed-off-by: Zhichang Yuan >>>> --- >>>> arch/arm64/mm/mmu.c | 5 ++++- >>>> 1 file changed, 4 insertions(+), 1 deletion(-) >>>> >>>> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c >>>> index f4f8b50..12a336b 100644 >>>> --- a/arch/arm64/mm/mmu.c >>>> +++ b/arch/arm64/mm/mmu.c >>>> @@ -191,8 +191,11 @@ static void __init alloc_init_pmd(pud_t *pud, unsigned long addr, >>>> * Check for previous table entries created during >>>> * boot (__create_page_tables) and flush them. >>>> */ >>>> - if (!pmd_none(old_pmd)) >>>> + if (!pmd_none(old_pmd)) { >>>> flush_tlb_all(); >>>> + if (pmd_table(old_pmd)) >>>> + memblock_free(pte_pfn(pmd_pte(old_pmd)) << PAGE_SHIFT, PAGE_SIZE); >>>> + } >>> For consistency with alloc_init_pud(), could you do: >>> >>> phys_addr_t table = __pa(pte_offset(&old_pmd, 0)); >>> memblock_free(table, PAGE_SIZE); >> Just as Laura comments, the pte_offset will convert the PA to VA, and >> then convert VA to PA. It seems to be verbose. That is why i use >> pte_pfn. Anyway, the consistency is better, i will revise it. >> >>> Since you are at this, for alloc_init_pud() could you please move the >>> flush_tlb_all() before memblock_free()? Theoretical problem really but >>> it's nice for consistency. >> As for this issue, i have a small question. Since the new PMD entry >> had been set by set_pmd, why not do the tlb flush as soon as we can? > So we need to flush the tlb shortly _after_ the new PMD or PUD has been > set to guarantee that a TLB load will see the new page table value. In > theory, we also need to flush it _before_ the old one is freed in case > the freed page is used by some other CPU (not a problem for boot code) > or some debug code poisons the freed page with a value that happens to > match a valid translation. > I misunderstood your comment before. I thought you ask me to make alloc_init_pmd consistent to alloc_init_pud. sorry for that! I will adjust the line sequence in alloc_init_pud too. Thanks!