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 9PC42eXM Ra87R1kSL25HjGi4nv0PZZzM7PyjcylpYK99fmO2pzPuMlHI= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Sep 04, 2025 at 01:22:51PM -0400, Liam R. Howlett wrote: > > > diff --git a/mm/mremap.c b/mm/mremap.c > > > index e618a706aff5..793fad58302c 100644 > > > --- a/mm/mremap.c > > > +++ b/mm/mremap.c > > > @@ -1040,7 +1040,7 @@ static unsigned long prep_move_vma(struct vma_remap_struct *vrm) > > > * We'd prefer to avoid failure later on in do_munmap: > > > * which may split one vma into three before unmapping. > > > */ > > > - if (current->mm->map_count >= sysctl_max_map_count - 3) > > > + if (exceeds_max_map_count(current->mm, 4)) > > > return -ENOMEM; > > > > In my version this would be: > > > > if (map_count_capacity(current->mm) < 4) > > return -ENOMEM; > > > > Someone could write map_count_capacity(current->mm) <= 4 and reintroduce > what this is trying to solve. And with the way it is written in this > patch, someone could pass in the wrong number. Right, but I think 'capacity' is pretty clear here, if the caller does something silly then that's on them... > > I'm not sure this is worth doing. There are places we allow the count > to go higher. ...But yeah, it's kinda borderline as to how useful this is. I _do_ however like the 'put map count in one place statically' rather than having a global, so a minimal version of this could be to just have a helper function that gets the sysctl_max_map_count, e.g.: if (current->mm->mmap_count >= max_map_count() - 3) etc. etc. > > Certainly fix the brk < to be <= and any other calculations, but the > rest seem okay as-is to me. The only real way to be sure we don't cause > a bug in the future is to have better testing. Speaking of testing - Kalesh - do make sure to test the VMA tests to make sure this doesn't break those - they live in tools/testing/vma and you just have to do make && ./vma Cheers! > > Thanks, > Liam