linux-kernel - Re: [RFC PATCH 2/6] mm/mmap: Abstract vma clean up from exit

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Message-ID: <2460fe1c-3e9a-465a-b164-12f92aabde00@lucifer.local>
Date: Thu, 4 Sep 2025 16:21:28 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: "Liam R. Howlett" <Liam.Howlett@...cle.com>,
        David Hildenbrand <david@...hat.com>, maple-tree@...ts.infradead.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Vlastimil Babka <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>,
        Suren Baghdasaryan <surenb@...gle.com>, Michal Hocko <mhocko@...e.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jann Horn <jannh@...gle.com>, Pedro Falcato <pfalcato@...e.de>,
        Charan Teja Kalla <quic_charante@...cinc.com>,
        shikemeng@...weicloud.com, kasong@...cent.com, nphamcs@...il.com,
        bhe@...hat.com, baohua@...nel.org, chrisl@...nel.org,
        Matthew Wilcox <willy@...radead.org>
Subject: Re: [RFC PATCH 2/6] mm/mmap: Abstract vma clean up from exit_mmap()

On Wed, Sep 03, 2025 at 03:56:03PM -0400, Liam R. Howlett wrote:
> * Lorenzo Stoakes <lorenzo.stoakes@...cle.com> [250819 14:38]:
> > On Fri, Aug 15, 2025 at 03:10:27PM -0400, Liam R. Howlett wrote:
> > > Create the new function tear_down_vmas() to remove a range of vmas.
> > > exit_mmap() will be removing all the vmas.
> > >
> > > This is necessary for future patches.
> > >
> > > No functional changes intended.
> > >
> > > Signed-off-by: Liam R. Howlett <Liam.Howlett@...cle.com>
> >
> > This function is pure and complete insanity, but this change looks
> > good. Couple nits below.
> >
> > Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
> >
> > > ---
> > >  mm/mmap.c | 37 ++++++++++++++++++++++++-------------
> > >  1 file changed, 24 insertions(+), 13 deletions(-)
> > >
> > > diff --git a/mm/mmap.c b/mm/mmap.c
> > > index c4c315b480af7..0995a48b46d59 100644
> > > --- a/mm/mmap.c
> > > +++ b/mm/mmap.c
> > > @@ -1250,6 +1250,29 @@ int vm_brk_flags(unsigned long addr, unsigned long request, vm_flags_t vm_flags)
> > >  }
> > >  EXPORT_SYMBOL(vm_brk_flags);
> > >
> > > +static inline
> > > +unsigned long tear_down_vmas(struct mm_struct *mm, struct vma_iterator *vmi,
> > > +		struct vm_area_struct *vma, unsigned long max)
> > > +{
> > > +	unsigned long nr_accounted = 0;
> > > +	int count = 0;
> > > +
> > > +	mmap_assert_write_locked(mm);
> > > +	vma_iter_set(vmi, vma->vm_end);
> > > +	do {
> > > +		if (vma->vm_flags & VM_ACCOUNT)
> > > +			nr_accounted += vma_pages(vma);
> > > +		vma_mark_detached(vma);
> > > +		remove_vma(vma);
> > > +		count++;
> > > +		cond_resched();
> > > +		vma = vma_next(vmi);
> > > +	} while (vma && vma->vm_end <= max);
> > > +
> > > +	BUG_ON(count != mm->map_count);
> >
> > Can we make this a WARN_ON() or WARN_ON_ONCE() while we're at it?
>
> Sure!

Thanks :)

>
> >
> > > +	return nr_accounted;
> > > +}
> > > +
> > >  /* Release all mmaps. */
> > >  void exit_mmap(struct mm_struct *mm)
> > >  {
> > > @@ -1257,7 +1280,6 @@ void exit_mmap(struct mm_struct *mm)
> > >  	struct vm_area_struct *vma;
> > >  	unsigned long nr_accounted = 0;
> >
> > No need to initialise this to 0 any more.
>
> There is a goto label below that skips calling the tear down, so this is
> still needed.

Ah yeah, sorry missed the goto destroy there. No worries then :)

>
> Thanks,
> Liam