Re: [PATCH v2 0/5] RDMA, IB: replace __get_free_pages() with kmalloc()

[Leon Romanovsky]

On Tue, Jul 14, 2026 at 03:24:56PM +0300, Leon Romanovsky wrote:
> On Mon, Jul 13, 2026 at 10:17:21AM +0300, Mike Rapoport (Microsoft) 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.
> > 
> > Also in git:
> > https://git.kernel.org/pub/scm/linux/kernel/git/rppt/linux.git gfp-to-kmalloc/rdma
> 
> Will you also change get_zeroed_page() in RDMA, or should I
> prepare a patch?

➜  kernel git:(wip/leon-for-next) git grep get_zeroed_page drivers/infiniband/
drivers/infiniband/hw/bnxt_re/ib_verbs.c:                       srq->uctx_srq_page = (void *)get_zeroed_page(GFP_KERNEL);
drivers/infiniband/hw/bnxt_re/ib_verbs.c:               cq->uctx_cq_page = (void *)get_zeroed_page(GFP_KERNEL);
drivers/infiniband/hw/bnxt_re/ib_verbs.c:       uctx->shpg = (void *)get_zeroed_page(GFP_KERNEL);
drivers/infiniband/hw/mlx4/mr.c:        mr->pages = (__be64 *)get_zeroed_page(GFP_KERNEL);
drivers/infiniband/hw/qedr/verbs.c:     q->db_rec_data = (void *)get_zeroed_page(GFP_USER);

Thanks

> 
> Thanks
> 
> > 
> > [1] https://lore.kernel.org/all/20251018093002.3660549-1-rppt@xxxxxxxxxx/
> > [2] https://lore.kernel.org/all/CA+55aFwp4iy4rtX2gE2WjBGFL=NxMVnoFeHqYa2j1dYOMMGqxg@xxxxxxxxxxxxxx/ 
> > 
> > ---
> > v2 changes:
> > * add comment to keep markers for sites that need "fast and as large as
> >   possible" allocation helper
> > 
> > v1: https://patch.msgid.link/20260630-b4-rdma-v1-0-ab42bcf0de92@xxxxxxxxxx
> > 
> > ---
> > Mike Rapoport (Microsoft) (5):
> >       RDMA/umem: ib_umem_get(): use kmalloc() to allocate page array
> >       RDMA/mlx5: replace __get_free_page() with kmalloc()
> >       IB/mthca: mthca_reg_user_mr(): use kmalloc() to allocate addresses array
> >       IB/mthca: allocate mthca_array memory with kzalloc()
> >       IB/rdmavt: use kzalloc() to allocate QPN-map pages
> > 
> >  drivers/infiniband/core/umem.c                | 5 +++--
> >  drivers/infiniband/hw/mlx5/odp.c              | 6 ++++--
> >  drivers/infiniband/hw/mthca/mthca_allocator.c | 6 +++---
> >  drivers/infiniband/hw/mthca/mthca_provider.c  | 5 +++--
> >  drivers/infiniband/sw/rdmavt/qp.c             | 8 ++++----
> >  5 files changed, 17 insertions(+), 13 deletions(-)
> > ---
> > base-commit: dc59e4fea9d83f03bad6bddf3fa2e52491777482
> > change-id: 20260610-b4-rdma-44625922fe16
> > 
> > --
> > Sincerely yours,
> > Mike.
> > 
>