Re: [PATCH v4 06/66] mm: Start tracking VMAs with maple tree

[Vlastimil Babka]

On 12/1/21 15:29, Liam Howlett wrote:
> From: "Liam R. Howlett" <Liam.Howlett@xxxxxxxxxx>
> 
> Start tracking the VMAs with the new maple tree structure in parallel
> with the rb_tree.  Add debug and trace events for maple tree operations
> and duplicate the rb_tree that is created on forks into the maple tree.
> 
> The maple tree is added to the mm_struct including the mm_init struct,
> added support in required mm/mmap functions, added tracking in
> kernel/fork for process forking, and used to find the unmapped_area and
> checked against what the rbtree finds.
> 
> Signed-off-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
> ---
>  arch/x86/kernel/tboot.c     |   1 +
>  drivers/firmware/efi/efi.c  |   1 +
>  include/linux/mm.h          |   2 +
>  include/linux/mm_types.h    |   3 +
>  include/trace/events/mmap.h |  71 ++++++++++++
>  init/main.c                 |   2 +
>  kernel/fork.c               |   5 +
>  mm/init-mm.c                |   2 +
>  mm/internal.h               |  73 ++++++++++++
>  mm/mmap.c                   | 220 +++++++++++++++++++++++++++++++++++-
>  10 files changed, 378 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kernel/tboot.c b/arch/x86/kernel/tboot.c
> index f9af561c3cd4..859e8d2ea070 100644
> --- a/arch/x86/kernel/tboot.c
> +++ b/arch/x86/kernel/tboot.c
> @@ -98,6 +98,7 @@ void __init tboot_probe(void)
>  static pgd_t *tboot_pg_dir;
>  static struct mm_struct tboot_mm = {
>  	.mm_rb          = RB_ROOT,
> +	.mm_mt          = MTREE_INIT_EXT(mm_mt, MM_MT_FLAGS, tboot_mm.mmap_lock),
>  	.pgd            = swapper_pg_dir,
>  	.mm_users       = ATOMIC_INIT(2),
>  	.mm_count       = ATOMIC_INIT(1),
> diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
> index ae79c3300129..0b40291416ca 100644
> --- a/drivers/firmware/efi/efi.c
> +++ b/drivers/firmware/efi/efi.c
> @@ -55,6 +55,7 @@ static unsigned long __initdata rt_prop = EFI_INVALID_TABLE_ADDR;
>  
>  struct mm_struct efi_mm = {
>  	.mm_rb			= RB_ROOT,
> +	.mm_mt			= MTREE_INIT_EXT(mm_mt, MM_MT_FLAGS, efi_mm.mmap_lock),
>  	.mm_users		= ATOMIC_INIT(2),
>  	.mm_count		= ATOMIC_INIT(1),
>  	.write_protect_seq      = SEQCNT_ZERO(efi_mm.write_protect_seq),
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index a7e4a9e7d807..9eae78a155be 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -2610,6 +2610,8 @@ extern bool arch_has_descending_max_zone_pfns(void);
>  /* nommu.c */
>  extern atomic_long_t mmap_pages_allocated;
>  extern int nommu_shrink_inode_mappings(struct inode *, size_t, size_t);
> +/* maple_tree */

Hm should it say mmap.c as that's where vma_store() is defined.

...

> diff --git a/mm/mmap.c b/mm/mmap.c
> index bfb0ea164a90..c2f1431886d4 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c

...

> @@ -1901,12 +2018,21 @@ static unsigned long unmapped_area(struct vm_unmapped_area_info *info)
>  	struct mm_struct *mm = current->mm;
>  	struct vm_area_struct *vma;
>  	unsigned long length, low_limit, high_limit, gap_start, gap_end;
> +	unsigned long gap;
> +	MA_STATE(mas, &mm->mm_mt, 0, 0);
>  
>  	/* Adjust search length to account for worst case alignment overhead */
>  	length = info->length + info->align_mask;
>  	if (length < info->length)
>  		return -ENOMEM;
>  
> +	rcu_read_lock();
> +	mas_empty_area_rev(&mas, info->low_limit, info->high_limit - 1,
> +			   length);

unmapped_area_topdown also uses mas_empty_area_rev(), shouldn't this one be
non-rev()?

> +	rcu_read_unlock();
> +	gap = mas.index;
> +	gap += (info->align_offset - gap) & info->align_mask;
> +
>  	/* Adjust search limits by the desired length */
>  	if (info->high_limit < length)
>  		return -ENOMEM;
> @@ -1988,20 +2114,39 @@ static unsigned long unmapped_area(struct vm_unmapped_area_info *info)
>  
>  	VM_BUG_ON(gap_start + info->length > info->high_limit);
>  	VM_BUG_ON(gap_start + info->length > gap_end);
> +
> +	VM_BUG_ON(gap != gap_start);
>  	return gap_start;
>  }
>  
> +static inline unsigned long top_area_aligned(struct vm_unmapped_area_info *info,
> +					     unsigned long end)
> +{
> +	return (end - info->length - info->align_offset) & (~info->align_mask);
> +}

Looks like this is never used anywhere and just deleted later in the series.

> +
>  static unsigned long unmapped_area_topdown(struct vm_unmapped_area_info *info)
>  {
>  	struct mm_struct *mm = current->mm;
> -	struct vm_area_struct *vma;
> +	struct vm_area_struct *vma = NULL;
>  	unsigned long length, low_limit, high_limit, gap_start, gap_end;
> +	unsigned long gap;
> +
> +	MA_STATE(mas, &mm->mm_mt, 0, 0);
> +	validate_mm_mt(mm);
>  
>  	/* Adjust search length to account for worst case alignment overhead */
>  	length = info->length + info->align_mask;
>  	if (length < info->length)
>  		return -ENOMEM;
>  
> +	rcu_read_lock();
> +	mas_empty_area_rev(&mas, info->low_limit, info->high_limit - 1,
> +		   length);
> +	rcu_read_unlock();
> +	gap = (mas.index + info->align_mask) & ~info->align_mask;
> +	gap -= info->align_offset & info->align_mask;
> +
>  	/*
>  	 * Adjust search limits by the desired length.
>  	 * See implementation comment at top of unmapped_area().