Re: [PATCH] mm/cma: print total and used pages in cma_alloc()

[Giorgi Tchankvetadze]

What about using tracepoints?
Add a trace_cma_alloc() event that only runs when tracing is enabled. No 
lock unless someone is actively monitoring

On 8/16/2025 10:27 AM, David Hildenbrand wrote:
> On 16.08.25 06:28, Xiang Gao wrote:
> > From: gaoxiang17 <gaoxiang17@xxxxxxxxxx>
> >
> > This makes cma info more intuitive during debugging.
> >
> > before:
> > [   24.407814] cma: cma_alloc(cma (____ptrval____), name: reserved, 
> > count 1, align 0)
> > [   24.413397] cma: cma_alloc(cma (____ptrval____), name: reserved, 
> > count 1, align 0)
> > [   24.415886] cma: cma_alloc(cma (____ptrval____), name: reserved, 
> > count 1, align 0)
> >
> > after:
> > [   24.069738] cma: cma_alloc(cma (____ptrval____), name: reserved, 
> > total pages: 16384, used pages: 64, request pages: 1, align 0)
> > [   24.075317] cma: cma_alloc(cma (____ptrval____), name: reserved, 
> > total pages: 16384, used pages: 65, request pages: 1, align 0)
> > [   24.078455] cma: cma_alloc(cma (____ptrval____), name: reserved, 
> > total pages: 16384, used pages: 66, request pages: 1, align 0)
> >
> > Signed-off-by: gaoxiang17 <gaoxiang17@xxxxxxxxxx>
> > ---
> >   mm/cma.c | 15 +++++++++++++--
> >   1 file changed, 13 insertions(+), 2 deletions(-)
> >
> > diff --git a/mm/cma.c b/mm/cma.c
> > index 2ffa4befb99a..46cc98e7f587 100644
> > --- a/mm/cma.c
> > +++ b/mm/cma.c
> > @@ -776,6 +776,17 @@ static void cma_debug_show_areas(struct cma *cma)
> >       spin_unlock_irq(&cma->lock);
> >   }
> > +static unsigned long cma_get_used_pages(struct cma *cma)
> > +{
> > +    unsigned long used;
> > +
> > +    spin_lock_irq(&cma->lock);
> > +    used = bitmap_weight(cma->bitmap, (int)cma_bitmap_maxno(cma));
> > +    spin_unlock_irq(&cma->lock);
> > +
> > +    return used << cma->order_per_bit;
> > +}
> > +
> >   static int cma_range_alloc(struct cma *cma, struct cma_memrange *cmr,
> >                   unsigned long count, unsigned int align,
> >                   struct page **pagep, gfp_t gfp)
> > @@ -858,8 +869,8 @@ static struct page *__cma_alloc(struct cma *cma, 
> > unsigned long count,
> >       if (!cma || !cma->count)
> >           return page;
> > -    pr_debug("%s(cma %p, name: %s, count %lu, align %d)\n", __func__,
> > -        (void *)cma, cma->name, count, align);
> > +    pr_debug("%s(cma %p, name: %s, total pages: %lu, used pages: %lu, 
> > request pages: %lu, align %d)\n",
> > +        __func__, (void *)cma, cma->name, cma->count, 
> > cma_get_used_pages(cma), count, align);
>
>          ^ one space missing for proper indentation.
>
> But doing another spinlock cycle just for debugging purposes? That does 
> not feel right, sorry.