Re: [PATCH 0/4] KVM: s390: replace page allocator calls with kzalloc()

[Claudio Imbrenda]

On Wed, 2 Sep 2026 16:17:03 +0300
Mike Rapoport <rppt@xxxxxxxxxx> wrote:

> On Wed, Sep 02, 2026 at 01:06:12PM +0200, Claudio Imbrenda wrote:
> > On Wed, 02 Sep 2026 09:15:12 +0300
> > "Mike Rapoport (Microsoft)" <rppt@xxxxxxxxxx> wrote:
> >   
> > > This is a (small) part of larger work of replacing page allocator calls
> > > with kmalloc.
> > > 
> > > My initial intention a few month ago was to remove ugly casts [1], but then
> > > willy pointed out that Linus objected to something like this [2] and it
> > > looks like more than a decade old technical debt.
> > > 
> > > Largely, anything that doesn't need struct page (or a memdesc in the
> > > future) should just use kmalloc() or kvmalloc() to allocate memory.
> > > kmalloc() guarantees alignment, physical contiguity and working
> > > virt_to_phys() and beside nicer API that returns void * on alloc and
> > > doesn't require to know the allocation size on free, kmalloc() provides
> > > better debugging capabilities than page allocator.
> > > 
> > > Another thing is that touching these allocation sites gives the reviewers
> > > opportunity to see if a PAGE_SIZE buffer is actually needed or maybe
> > > another size is appropriate.
> > > 
> > > For larger allocations that don't need physically contiguous memory
> > > kvmalloc() can be a better option that __get_free_pages() because under
> > > memory pressure it's is easier to allocate several order-0 pages than a
> > > physically contiguous chunk with the same number of pages.
> > > 
> > > And last, but not least, removing needless calls to page allocator should
> > > help with memdesc (aka project folio) conversion. There will be way less
> > > places to audit to see if the user was actually using struct page.  
> > 
> > I have some objections to this series, but not because of what you are
> > trying to do (which is actually nice).
> > 
> > I understand that you probably wanted to touch as little code as
> > possible,  
> 
> Yep :)
> 
> > but now since you're rewriting the allocations to use
> > kmalloc.... I'd like them to be converted to use the __free(kvmalloc)  
> 
> You mean __free(kfree)? Sure, I can look into it.

yep :)

> 
> > system. It will make the code smaller, easier to read and understand,
> > less prone to future errors, etc.
> > 
> > In some places the whole code flow can be simplified a lot.  
>