linux-kernel - Re: [PATCH v4 56/66] mm/mlock: Use maple tree iterators instead of vma linked list

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Date:   Wed, 26 Jan 2022 16:41:11 +0000
From:   Liam Howlett <liam.howlett@...cle.com>
To:     Vlastimil Babka <vbabka@...e.cz>
CC:     "maple-tree@...ts.infradead.org" <maple-tree@...ts.infradead.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Song Liu <songliubraving@...com>,
        Davidlohr Bueso <dave@...olabs.net>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Matthew Wilcox <willy@...radead.org>,
        Laurent Dufour <ldufour@...ux.ibm.com>,
        David Rientjes <rientjes@...gle.com>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Rik van Riel <riel@...riel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Michel Lespinasse <walken.cr@...il.com>,
        Jerome Glisse <jglisse@...hat.com>,
        Minchan Kim <minchan@...gle.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Rom Lemarchand <romlem@...gle.com>
Subject: Re: [PATCH v4 56/66] mm/mlock: Use maple tree iterators instead of
 vma linked list

* Vlastimil Babka <vbabka@...e.cz> [220120 07:16]:
> On 12/1/21 15:30, Liam Howlett wrote:
> > From: "Liam R. Howlett" <Liam.Howlett@...cle.com>
> > 
> > Signed-off-by: Liam R. Howlett <Liam.Howlett@...cle.com>
> > ---
> >  mm/mlock.c | 19 +++++++++----------
> >  1 file changed, 9 insertions(+), 10 deletions(-)
> > 
> > diff --git a/mm/mlock.c b/mm/mlock.c
> > index e263d62ae2d0..feb691eb4c64 100644
> > --- a/mm/mlock.c
> > +++ b/mm/mlock.c
> > @@ -563,6 +563,7 @@ static int apply_vma_lock_flags(unsigned long start, size_t len,
> >  	unsigned long nstart, end, tmp;
> >  	struct vm_area_struct *vma, *prev;
> >  	int error;
> > +	MA_STATE(mas, &current->mm->mm_mt, start, start);
> >  
> >  	VM_BUG_ON(offset_in_page(start));
> >  	VM_BUG_ON(len != PAGE_ALIGN(len));
> > @@ -571,11 +572,11 @@ static int apply_vma_lock_flags(unsigned long start, size_t len,
> >  		return -EINVAL;
> >  	if (end == start)
> >  		return 0;
> > -	vma = find_vma(current->mm, start);
> > -	if (!vma || vma->vm_start > start)
> > +	vma = mas_walk(&mas);
> > +	if (!vma)
> >  		return -ENOMEM;
> >  
> > -	prev = vma->vm_prev;
> > +	prev = mas_prev(&mas, 0);
> 
> Could be only done as an 'else' of the 'if' below?

Agreed.  I will make that change.

> 
> >  	if (start > vma->vm_start)
> >  		prev = vma;
> >  
> > @@ -597,7 +598,7 @@ static int apply_vma_lock_flags(unsigned long start, size_t len,
> >  		if (nstart >= end)
> >  			break;
> >  
> > -		vma = prev->vm_next;
> > +		vma = find_vma(prev->vm_mm, prev->vm_end);
> >  		if (!vma || vma->vm_start != nstart) {
> >  			error = -ENOMEM;
> >  			break;
> > @@ -618,15 +619,12 @@ static unsigned long count_mm_mlocked_page_nr(struct mm_struct *mm,
> >  {
> >  	struct vm_area_struct *vma;
> >  	unsigned long count = 0;
> > +	MA_STATE(mas, &mm->mm_mt, start, start);
> >  
> >  	if (mm == NULL)
> >  		mm = current->mm;
> >  
> > -	vma = find_vma(mm, start);
> > -	if (vma == NULL)
> > -		return 0;
> > -
> > -	for (; vma ; vma = vma->vm_next) {
> > +	mas_for_each(&mas, vma, start + len) {
> 
> Could be for_each_vma_range()?

yes, I will do this.

> 
> >  		if (start >= vma->vm_end)
> >  			continue;
> 
> Unnecessary? (even before this patch, I think?)

I think so too, I will remove it.

> 
> >  		if (start + len <=  vma->vm_start)
> 
> Unnecessary after your patch?

This appears to be for overflow.  My patch will not deal with overflow
as it is dealt with today.  I will update my patch to deal with overflow
in the same way by removing this from the loop & setting up an end
variable.  This will have the added benefit of reducing the loop for a
one time check.  I don't love the fact that overflow is handled like
this.  Perhaps this should be revisited at a later date.

> 
> > @@ -741,6 +739,7 @@ static int apply_mlockall_flags(int flags)
> >  {
> >  	struct vm_area_struct *vma, *prev = NULL;
> >  	vm_flags_t to_add = 0;
> > +	unsigned long addr = 0;
> >  
> >  	current->mm->def_flags &= VM_LOCKED_CLEAR_MASK;
> >  	if (flags & MCL_FUTURE) {
> > @@ -759,7 +758,7 @@ static int apply_mlockall_flags(int flags)
> >  			to_add |= VM_LOCKONFAULT;
> >  	}
> >  
> > -	for (vma = current->mm->mmap; vma ; vma = prev->vm_next) {
> > +	mt_for_each(&current->mm->mm_mt, vma, addr, ULONG_MAX) {

and I'll add a for_each_vma() here.

> >  		vm_flags_t newflags;
> >  
> >  		newflags = vma->vm_flags & VM_LOCKED_CLEAR_MASK;
>