Re: [RFC 3/3] mm: integrate GCMA with CMA using dt-bindings

[Suren Baghdasaryan <surenb@google.com>]

On Fri, Mar 21, 2025 at 7:06 AM Conor Dooley <conor@kernel.org> wrote:
>
> On Thu, Mar 20, 2025 at 10:39:31AM -0700, Suren Baghdasaryan wrote:
> > This patch introduces a new "guarantee" property for shared-dma-pool.
> > With this property, admin can create specific memory pool as
> > GCMA-based CMA if they care about allocation success rate and latency.
> > The downside of GCMA is that it can host only clean file-backed pages
> > since it's using cleancache as its secondary user.
> >
> > Signed-off-by: Minchan Kim <minchan@google.com>
> > Signed-off-by: Suren Baghdasaryan <surenb@google.com>
> > ---
> >  arch/powerpc/kernel/fadump.c |  2 +-
> >  include/linux/cma.h          |  2 +-
> >  kernel/dma/contiguous.c      | 11 ++++++++++-
> >  mm/cma.c                     | 33 ++++++++++++++++++++++++++-------
> >  mm/cma.h                     |  1 +
> >  mm/cma_sysfs.c               | 10 ++++++++++
> >  6 files changed, 49 insertions(+), 10 deletions(-)
> >
> > diff --git a/arch/powerpc/kernel/fadump.c b/arch/powerpc/kernel/fadump.c
> > index 4b371c738213..4eb7be0cdcdb 100644
> > --- a/arch/powerpc/kernel/fadump.c
> > +++ b/arch/powerpc/kernel/fadump.c
> > @@ -111,7 +111,7 @@ void __init fadump_cma_init(void)
> >               return;
> >       }
> >
> > -     rc = cma_init_reserved_mem(base, size, 0, "fadump_cma", &fadump_cma);
> > +     rc = cma_init_reserved_mem(base, size, 0, "fadump_cma", &fadump_cma, false);
> >       if (rc) {
> >               pr_err("Failed to init cma area for firmware-assisted dump,%d\n", rc);
> >               /*
> > diff --git a/include/linux/cma.h b/include/linux/cma.h
> > index 62d9c1cf6326..3207db979e94 100644
> > --- a/include/linux/cma.h
> > +++ b/include/linux/cma.h
> > @@ -46,7 +46,7 @@ extern int __init cma_declare_contiguous_multi(phys_addr_t size,
> >  extern int cma_init_reserved_mem(phys_addr_t base, phys_addr_t size,
> >                                       unsigned int order_per_bit,
> >                                       const char *name,
> > -                                     struct cma **res_cma);
> > +                                     struct cma **res_cma, bool gcma);
> >  extern struct page *cma_alloc(struct cma *cma, unsigned long count, unsigned int align,
> >                             bool no_warn);
> >  extern bool cma_pages_valid(struct cma *cma, const struct page *pages, unsigned long count);
> > diff --git a/kernel/dma/contiguous.c b/kernel/dma/contiguous.c
> > index 055da410ac71..a68b3123438c 100644
> > --- a/kernel/dma/contiguous.c
> > +++ b/kernel/dma/contiguous.c
> > @@ -459,6 +459,7 @@ static int __init rmem_cma_setup(struct reserved_mem *rmem)
> >       unsigned long node = rmem->fdt_node;
> >       bool default_cma = of_get_flat_dt_prop(node, "linux,cma-default", NULL);
> >       struct cma *cma;
> > +     bool gcma;
> >       int err;
> >
> >       if (size_cmdline != -1 && default_cma) {
> > @@ -476,7 +477,15 @@ static int __init rmem_cma_setup(struct reserved_mem *rmem)
> >               return -EINVAL;
> >       }
> >
> > -     err = cma_init_reserved_mem(rmem->base, rmem->size, 0, rmem->name, &cma);
> > +     gcma = !!of_get_flat_dt_prop(node, "guarantee", NULL);
>
> When this (or if I guess) this goes !RFC, you will need to document this
> new property that you're adding.

Definitely. I'll document the cleancache and GCMA as well.
Thanks!