Subject: Re: [PATCH v2 1/6] powerpc: prefer memblock APIs returning virtual address

From: Mike Rapoport <[email-masked]>
Date: Tue, 4 Dec 2018 19:13:28 +0200

On Tue, Dec 04, 2018 at 08:59:41PM +1100, Michael Ellerman wrote:
> Hi Mike,
> 
> Thanks for trying to clean these up.
> 
> I think a few could be improved though ...
> 
> Mike Rapoport <[email-masked]> writes:
> > diff --git a/arch/powerpc/kernel/paca.c b/arch/powerpc/kernel/paca.c
> > index 913bfca..fa884ad 100644
> > --- a/arch/powerpc/kernel/paca.c
> > +++ b/arch/powerpc/kernel/paca.c
> > @@ -42,17 +42,15 @@ static void *__init alloc_paca_data(unsigned long size, unsigned long align,
> >  		nid = early_cpu_to_node(cpu);
> >  	}
> >  
> > -	pa = memblock_alloc_base_nid(size, align, limit, nid, MEMBLOCK_NONE);
> > -	if (!pa) {
> > -		pa = memblock_alloc_base(size, align, limit);
> > -		if (!pa)
> > -			panic("cannot allocate paca data");
> > -	}
> > +	ptr = memblock_alloc_try_nid_raw(size, align, MEMBLOCK_LOW_LIMIT,
> > +					 limit, nid);
> > +	if (!ptr)
> > +		panic("cannot allocate paca data");
>   
> The old code doesn't zero, but two of the three callers of
> alloc_paca_data() *do* zero the whole allocation, so I'd be happy if we
> did it in here instead.

I looked at the callers and couldn't tell if zeroing memory in
init_lppaca() would be ok.
I'll remove the _raw here.
 
> That would mean we could use memblock_alloc_try_nid() avoiding the need
> to panic() manually.

Actual, my plan was to remove panic() from all memblock_alloc* and make all
callers to check the returned value.
I believe it's cleaner and also allows more meaningful panic messages. Not
mentioning the reduction of memblock code.
 
> > diff --git a/arch/powerpc/kernel/setup_64.c b/arch/powerpc/kernel/setup_64.c
> > index 236c115..d11ee7f 100644
> > --- a/arch/powerpc/kernel/setup_64.c
> > +++ b/arch/powerpc/kernel/setup_64.c
> > @@ -634,19 +634,17 @@ __init u64 ppc64_bolted_size(void)
> >  
> >  static void *__init alloc_stack(unsigned long limit, int cpu)
> >  {
> > -	unsigned long pa;
> > +	void *ptr;
> >  
> >  	BUILD_BUG_ON(STACK_INT_FRAME_SIZE % 16);
> >  
> > -	pa = memblock_alloc_base_nid(THREAD_SIZE, THREAD_SIZE, limit,
> > -					early_cpu_to_node(cpu), MEMBLOCK_NONE);
> > -	if (!pa) {
> > -		pa = memblock_alloc_base(THREAD_SIZE, THREAD_SIZE, limit);
> > -		if (!pa)
> > -			panic("cannot allocate stacks");
> > -	}
> > +	ptr = memblock_alloc_try_nid_raw(THREAD_SIZE, THREAD_SIZE,
> > +					 MEMBLOCK_LOW_LIMIT, limit,
> > +					 early_cpu_to_node(cpu));
> > +	if (!ptr)
> > +		panic("cannot allocate stacks");
>  
> Similarly here, several of the callers zero the stack, and I'd rather
> all of them did.
> 
> So again we could use memblock_alloc_try_nid() here and remove the
> memset()s from emergency_stack_init().

Ok
 
> > diff --git a/arch/powerpc/mm/pgtable-radix.c b/arch/powerpc/mm/pgtable-radix.c
> > index 9311560..415a1eb0 100644
> > --- a/arch/powerpc/mm/pgtable-radix.c
> > +++ b/arch/powerpc/mm/pgtable-radix.c
> > @@ -51,24 +51,18 @@ static int native_register_process_table(unsigned long base, unsigned long pg_sz
> >  static __ref void *early_alloc_pgtable(unsigned long size, int nid,
> >  			unsigned long region_start, unsigned long region_end)
> >  {
> > -	unsigned long pa = 0;
> > +	phys_addr_t min_addr = MEMBLOCK_LOW_LIMIT;
> > +	phys_addr_t max_addr = MEMBLOCK_ALLOC_ANYWHERE;
> >  	void *pt;
> >  
> > -	if (region_start || region_end) /* has region hint */
> > -		pa = memblock_alloc_range(size, size, region_start, region_end,
> > -						MEMBLOCK_NONE);
> > -	else if (nid != -1) /* has node hint */
> > -		pa = memblock_alloc_base_nid(size, size,
> > -						MEMBLOCK_ALLOC_ANYWHERE,
> > -						nid, MEMBLOCK_NONE);
> > +	if (region_start)
> > +		min_addr = region_start;
> > +	if (region_end)
> > +		max_addr = region_end;
> >  
> > -	if (!pa)
> > -		pa = memblock_alloc_base(size, size, MEMBLOCK_ALLOC_ANYWHERE);
> > -
> > -	BUG_ON(!pa);
> > -
> > -	pt = __va(pa);
> > -	memset(pt, 0, size);
> > +	pt = memblock_alloc_try_nid_nopanic(size, size, min_addr, max_addr,
> > +					    nid);
> > +	BUG_ON(!pt);
> 
> I don't think there's any reason to BUG_ON() here rather than letting
> memblock() call panic() for us. So this could also be memblock_alloc_try_nid().

I'd prefer to panic here.
 
> > diff --git a/arch/powerpc/platforms/pasemi/iommu.c b/arch/powerpc/platforms/pasemi/iommu.c
> > index f297152..f62930f 100644
> > --- a/arch/powerpc/platforms/pasemi/iommu.c
> > +++ b/arch/powerpc/platforms/pasemi/iommu.c
> > @@ -208,7 +208,9 @@ static int __init iob_init(struct device_node *dn)
> >  	pr_debug(" -> %s\n", __func__);
> >  
> >  	/* For 2G space, 8x64 pages (2^21 bytes) is max total l2 size */
> > -	iob_l2_base = (u32 *)__va(memblock_alloc_base(1UL<<21, 1UL<<21, 0x80000000));
> > +	iob_l2_base = memblock_alloc_try_nid_raw(1UL << 21, 1UL << 21,
> > +					MEMBLOCK_LOW_LIMIT, 0x80000000,
> > +					NUMA_NO_NODE);
> 
> This isn't equivalent is it?
> 
> memblock_alloc_base() panics on failure but memblock_alloc_try_nid_raw()
> doesn't?

Right, this should be either a memblock function that panic()'s or a call
to panic() if the returned value is NULL.
My preference is for the second variant :)
 
> Same comment for the other locations that do that conversion.
> 
> cheers
> 

-- 
Sincerely yours,
Mike.