lkml.org 
[lkml]   [2017]   [Nov]   [3]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] s390/mm: fix pud table accounting
On Fri 03-11-17 10:05:51, Heiko Carstens wrote:
> With "mm: account pud page tables" and "mm: consolidate page table
> accounting" pud page table accounting was introduced which now results
> in tons of warnings like this one on s390:
>
> BUG: non-zero pgtables_bytes on freeing mm: -16384
>
> Reason for this are our run-time folded page tables: by default new
> processes start with three page table levels where the allocated pgd
> is the same as the first pud. In this case there won't ever be a pud
> allocated and therefore mm_inc_nr_puds() will also never be called.
>
> However when freeing the address space free_pud_range() will call
> exactly once mm_dec_nr_puds() which leads to misaccounting.
>
> Therefore call mm_inc_nr_puds() within init_new_context() to fix
> this. This is the same like we have it already for processes that run
> with two page table levels (aka compat processes).
>
> While at it also adjust the comment, since there is no "mm->nr_pmds"
> anymore.

Subtle...

Thanks for the fix, I didn't have any idea about this when reviewing.

> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Gerald Schaefer <gerald.schaefer@de.ibm.com>
> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
> Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
> ---
> arch/s390/include/asm/mmu_context.h | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/arch/s390/include/asm/mmu_context.h b/arch/s390/include/asm/mmu_context.h
> index 3c9abedc323c..4f943d58cbac 100644
> --- a/arch/s390/include/asm/mmu_context.h
> +++ b/arch/s390/include/asm/mmu_context.h
> @@ -43,6 +43,8 @@ static inline int init_new_context(struct task_struct *tsk,
> mm->context.asce_limit = STACK_TOP_MAX;
> mm->context.asce = __pa(mm->pgd) | _ASCE_TABLE_LENGTH |
> _ASCE_USER_BITS | _ASCE_TYPE_REGION3;
> + /* pgd_alloc() did not account this pud */
> + mm_inc_nr_puds(mm);
> break;
> case -PAGE_SIZE:
> /* forked 5-level task, set new asce with new_mm->pgd */
> @@ -58,7 +60,7 @@ static inline int init_new_context(struct task_struct *tsk,
> /* forked 2-level compat task, set new asce with new mm->pgd */
> mm->context.asce = __pa(mm->pgd) | _ASCE_TABLE_LENGTH |
> _ASCE_USER_BITS | _ASCE_TYPE_SEGMENT;
> - /* pgd_alloc() did not increase mm->nr_pmds */
> + /* pgd_alloc() did not account this pmd */
> mm_inc_nr_pmds(mm);
> }
> crst_table_init((unsigned long *) mm->pgd, pgd_entry_type(mm));
> --
> 2.13.5
>

--
Michal Hocko
SUSE Labs

\
 
 \ /
  Last update: 2017-11-03 10:17    [W:0.058 / U:0.064 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site