Re: [PATCH 03/11] x86/mm/hotplug: Don't remove PGD entries in remove_pagetable()

Kamezawa Hiroyuki
2015-10-06T03:46:08Z

On 2015/09/22 15:23, Ingo Molnar wrote:
> So when memory hotplug removes a piece of physical memory from pagetable
> mappings, it also frees the underlying PGD entry.
>
> This complicates PGD management, so don't do this. We can keep the
> PGD mapped and the PUD table all clear - it's only a single 4K page
> per 512 GB of memory hotplugged.
>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Andy Lutomirski <luto@amacapital.net>
> Cc: Borislav Petkov <bp@alien8.de>
> Cc: Brian Gerst <brgerst@gmail.com>
> Cc: Denys Vlasenko <dvlasenk@redhat.com>
> Cc: H. Peter Anvin <hpa@zytor.com>
> Cc: Linus Torvalds <torvalds@linux-foundation.org>
> Cc: Oleg Nesterov <oleg@redhat.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Rik van Riel <riel@redhat.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Waiman Long <Waiman.Long@hp.com>
> Cc: linux-mm@kvack.org
> Signed-off-by: Ingo Molnar <mingo@kernel.org>

Ishimatsu-san, Tang-san, please check.

Doesn't this patch affects the issues of
5255e0a79fcc0ff47b387af92bd9ef5729b1b859
9661d5bcd058fe15b4138a00d96bd36516134543

?

-Kame

> ---
> arch/x86/mm/init_64.c | 27 ---------------------------
> 1 file changed, 27 deletions(-)
>
> diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
> index 7129e7647a76..60b0cc3f2819 100644
> --- a/arch/x86/mm/init_64.c
> +++ b/arch/x86/mm/init_64.c
> @@ -780,27 +780,6 @@ static void __meminit free_pmd_table(pmd_t *pmd_start, pud_t *pud)
> spin_unlock(&init_mm.page_table_lock);
> }
>
> -/* Return true if pgd is changed, otherwise return false. */
> -static bool __meminit free_pud_table(pud_t *pud_start, pgd_t *pgd)
> -{
> - pud_t *pud;
> - int i;
> -
> - for (i = 0; i < PTRS_PER_PUD; i++) {
> - pud = pud_start + i;
> - if (pud_val(*pud))
> - return false;
> - }
> -
> - /* free a pud table */
> - free_pagetable(pgd_page(*pgd), 0);
> - spin_lock(&init_mm.page_table_lock);
> - pgd_clear(pgd);
> - spin_unlock(&init_mm.page_table_lock);
> -
> - return true;
> -}
> -
> static void __meminit
> remove_pte_table(pte_t *pte_start, unsigned long addr, unsigned long end,
> bool direct)
> @@ -992,7 +971,6 @@ remove_pagetable(unsigned long start, unsigned long end, bool direct)
> unsigned long addr;
> pgd_t *pgd;
> pud_t *pud;
> - bool pgd_changed = false;
>
> for (addr = start; addr < end; addr = next) {
> next = pgd_addr_end(addr, end);
> @@ -1003,13 +981,8 @@ remove_pagetable(unsigned long start, unsigned long end, bool direct)
>
> pud = (pud_t *)pgd_page_vaddr(*pgd);
> remove_pud_table(pud, addr, next, direct);
> - if (free_pud_table(pud, pgd))
> - pgd_changed = true;
> }
>
> - if (pgd_changed)
> - sync_global_pgds(start, end - 1, 1);
> -
> flush_tlb_all();
> }
>
>