Re: [PATCH v4 55/66] mm/mempolicy: Use maple tree iterators instead of vma linked list

[Liam Howlett <liam.howlett@oracle.com>]

* Vlastimil Babka <vbabka@suse.cz> [220120 06:58]:
> On 12/1/21 15:30, Liam Howlett wrote:
> > From: "Liam R. Howlett" <Liam.Howlett@Oracle.com>
> > 
> > Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> > Signed-off-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
> > ---
> >  mm/mempolicy.c | 53 ++++++++++++++++++++++++++------------------------
> >  1 file changed, 28 insertions(+), 25 deletions(-)
> > 
> > diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> > index 10e9c87260ed..0e2d918f4f30 100644
> > --- a/mm/mempolicy.c
> > +++ b/mm/mempolicy.c
> > @@ -377,9 +377,10 @@ void mpol_rebind_task(struct task_struct *tsk, const nodemask_t *new)
> >  void mpol_rebind_mm(struct mm_struct *mm, nodemask_t *new)
> >  {
> >  	struct vm_area_struct *vma;
> > +	MA_STATE(mas, &mm->mm_mt, 0, 0);
> 
> VMA_ITERATOR?

Yes, I will make this change.  Thanks.

> 
> >  
> >  	mmap_write_lock(mm);
> > -	for (vma = mm->mmap; vma; vma = vma->vm_next)
> > +	mas_for_each(&mas, vma, ULONG_MAX)
> >  		mpol_rebind_policy(vma->vm_policy, new);
> >  	mmap_write_unlock(mm);
> >  }
> > @@ -652,7 +653,7 @@ static unsigned long change_prot_numa(struct vm_area_struct *vma,
> >  static int queue_pages_test_walk(unsigned long start, unsigned long end,
> >  				struct mm_walk *walk)
> >  {
> > -	struct vm_area_struct *vma = walk->vma;
> > +	struct vm_area_struct *next, *vma = walk->vma;
> >  	struct queue_pages *qp = walk->private;
> >  	unsigned long endvma = vma->vm_end;
> >  	unsigned long flags = qp->flags;
> > @@ -667,9 +668,10 @@ static int queue_pages_test_walk(unsigned long start, unsigned long end,
> >  			/* hole at head side of range */
> >  			return -EFAULT;
> >  	}
> > +	next = find_vma(vma->vm_mm, vma->vm_end);
> >  	if (!(flags & MPOL_MF_DISCONTIG_OK) &&
> >  		((vma->vm_end < qp->end) &&
> > -		(!vma->vm_next || vma->vm_end < vma->vm_next->vm_start)))
> > +		(!next || vma->vm_end < next->vm_start)))
> >  		/* hole at middle or tail of range */
> >  		return -EFAULT;
> >  
> > @@ -783,28 +785,24 @@ static int vma_replace_policy(struct vm_area_struct *vma,
> >  static int mbind_range(struct mm_struct *mm, unsigned long start,
> >  		       unsigned long end, struct mempolicy *new_pol)
> >  {
> > -	struct vm_area_struct *next;
> > +	MA_STATE(mas, &mm->mm_mt, start - 1, start - 1);
> >  	struct vm_area_struct *prev;
> >  	struct vm_area_struct *vma;
> >  	int err = 0;
> >  	pgoff_t pgoff;
> > -	unsigned long vmstart;
> > -	unsigned long vmend;
> > -
> > -	vma = find_vma(mm, start);
> > -	VM_BUG_ON(!vma);
> >  
> > -	prev = vma->vm_prev;
> > -	if (start > vma->vm_start)
> > -		prev = vma;
> > +	prev = mas_find_rev(&mas, 0);
> > +	if (prev && (start < prev->vm_end))
> > +		vma = prev;
> > +	else
> > +		vma = mas_next(&mas, end - 1);
> >  
> > -	for (; vma && vma->vm_start < end; prev = vma, vma = next) {
> > -		next = vma->vm_next;
> > -		vmstart = max(start, vma->vm_start);
> > -		vmend   = min(end, vma->vm_end);
> > +	do {
> > +		unsigned long vmstart = max(start, vma->vm_start);
> > +		unsigned long vmend = min(end, vma->vm_end);
> 
> What if vma is null? Shouldn't this rather be a "for (; vma; vma =
> mas_next(...)"

We have already found the vma above.  I am re-using the maple state to
save walking the tree.  I will re-add the VM_BUG_ON(!vma), but I think
it's more efficient the way it is.

> 
> >  
> >  		if (mpol_equal(vma_policy(vma), new_pol))
> > -			continue;
> > +			goto next;
> >  
> >  		pgoff = vma->vm_pgoff +
> >  			((vmstart - vma->vm_start) >> PAGE_SHIFT);
> > @@ -812,8 +810,8 @@ static int mbind_range(struct mm_struct *mm, unsigned long start,
> >  				 vma->anon_vma, vma->vm_file, pgoff,
> >  				 new_pol, vma->vm_userfaultfd_ctx);
> >  		if (prev) {
> > +			mas_pause(&mas);
> >  			vma = prev;
> > -			next = vma->vm_next;
> >  			if (mpol_equal(vma_policy(vma), new_pol))
> >  				continue;
> >  			/* vma_merge() joined vma && vma->next, case 8 */
> > @@ -823,19 +821,23 @@ static int mbind_range(struct mm_struct *mm, unsigned long start,
> >  			err = split_vma(vma->vm_mm, vma, vmstart, 1);
> >  			if (err)
> >  				goto out;
> > +			mas_pause(&mas);
> >  		}
> >  		if (vma->vm_end != vmend) {
> >  			err = split_vma(vma->vm_mm, vma, vmend, 0);
> >  			if (err)
> >  				goto out;
> > +			/* mas_pause() unnecessary as the loop is ending */
> >  		}
> > - replace:
> > +replace:
> >  		err = vma_replace_policy(vma, new_pol);
> >  		if (err)
> >  			goto out;
> > -	}
> > +next:
> > +		prev = vma;
> > +	} while ((vma = mas_next(&mas, end - 1)) != NULL);
> >  
> > - out:
> > +out:
> >  	return err;
> >  }
> >  
> > @@ -1053,6 +1055,7 @@ static int migrate_to_node(struct mm_struct *mm, int source, int dest,
> >  			   int flags)
> >  {
> >  	nodemask_t nmask;
> > +	struct vm_area_struct *vma;
> >  	LIST_HEAD(pagelist);
> >  	int err = 0;
> >  	struct migration_target_control mtc = {
> > @@ -1068,8 +1071,9 @@ static int migrate_to_node(struct mm_struct *mm, int source, int dest,
> >  	 * need migration.  Between passing in the full user address
> >  	 * space range and MPOL_MF_DISCONTIG_OK, this call can not fail.
> >  	 */
> > +	vma = find_vma(mm, 0);
> >  	VM_BUG_ON(!(flags & (MPOL_MF_MOVE | MPOL_MF_MOVE_ALL)));
> > -	queue_pages_range(mm, mm->mmap->vm_start, mm->task_size, &nmask,
> > +	queue_pages_range(mm, vma->vm_start, mm->task_size, &nmask,
> >  			flags | MPOL_MF_DISCONTIG_OK, &pagelist);
> >  
> >  	if (!list_empty(&pagelist)) {
> > @@ -1198,13 +1202,12 @@ static struct page *new_page(struct page *page, unsigned long start)
> >  {
> >  	struct vm_area_struct *vma;
> >  	unsigned long address;
> > +	MA_STATE(mas, &current->mm->mm_mt, start, start);
> >  
> > -	vma = find_vma(current->mm, start);
> > -	while (vma) {
> > +	mas_for_each(&mas, vma, ULONG_MAX) {
> >  		address = page_address_in_vma(page, vma);
> >  		if (address != -EFAULT)
> >  			break;
> > -		vma = vma->vm_next;
> >  	}
> >  
> >  	if (PageHuge(page)) {
>