Re: [PATCH v3 4/4] mm: perform VMA allocation, freeing, duplication in mm

[Andrew Morton]

On Wed, 30 Apr 2025 10:20:10 +0100 Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx> wrote:

> On Tue, Apr 29, 2025 at 09:22:59AM +0200, Vlastimil Babka wrote:
> > On 4/28/25 17:28, Lorenzo Stoakes wrote:
> > > Right now these are performed in kernel/fork.c which is odd and a violation
> > > of separation of concerns, as well as preventing us from integrating this
> > > and related logic into userland VMA testing going forward, and perhaps more
> > > importantly - enabling us to, in a subsequent commit, make VMA
> > > allocation/freeing a purely internal mm operation.
> >
> > I wonder if the last part is from an earlier version and now obsolete
> > because there's not subsequent commit in this series and the placement of
> > alloc/freeing in vma_init.c seems making those purely internal mm operations
> > already? Or do you mean some further plans?
> >
> 
> Sorry, missed this!
> 
> Andrew - could we delete the last part of this sentence so it reads:
> 
> Right now these are performed in kernel/fork.c which is odd and a violation
> of separation of concerns, as well as preventing us from integrating this
> and related logic into userland VMA testing going forward.

Sure.  The result:

: Right now these are performed in kernel/fork.c which is odd and a
: violation of separation of concerns, as well as preventing us from
: integrating this and related logic into userland VMA testing going
: forward.
: 
: There is a fly in the ointment - nommu - mmap.c is not compiled if
: CONFIG_MMU not set, and neither is vma.c.
: 
: To square the circle, let's add a new file - vma_init.c.  This will be
: compiled for both CONFIG_MMU and nommu builds, and will also form part of
: the VMA userland testing.
: 
: This allows us to de-duplicate code, while maintaining separation of
: concerns and the ability for us to userland test this logic.
: 
: Update the VMA userland tests accordingly, additionally adding a
: detach_free_vma() helper function to correctly detach VMAs before freeing
: them in test code, as this change was triggering the assert for this.