Re: [PATCH] memblock: stop using implicit alignement to SMP_CACHE_BYTES

Re: [PATCH] memblock: stop using implicit alignement to SMP_CACHE_BYTES

[Benjamin Herrenschmidt]

On Fri, 2018-10-05 at 00:07 +0300, Mike Rapoport wrote:
> When a memblock allocation APIs are called with align = 0, the alignment is
> implicitly set to SMP_CACHE_BYTES.
> 
> Replace all such uses of memblock APIs with the 'align' parameter explicitly
> set to SMP_CACHE_BYTES and stop implicit alignment assignment in the
> memblock internal allocation functions.
> 
> For the case when memblock APIs are used via helper functions, e.g. like
> iommu_arena_new_node() in Alpha, the helper functions were detected with
> Coccinelle's help and then manually examined and updated where appropriate.
> 
> The direct memblock APIs users were updated using the semantic patch below:

What is the purpose of this ? It sounds rather counter-intuitive...

Ben.

Re: [PATCH] memblock: stop using implicit alignement to SMP_CACHE_BYTES

[Mike Rapoport]

On October 5, 2018 6:25:38 AM GMT+03:00, Benjamin Herrenschmidt <benh@kernel.crashing.org> wrote:
>On Fri, 2018-10-05 at 00:07 +0300, Mike Rapoport wrote:
>> When a memblock allocation APIs are called with align = 0, the
>alignment is
>> implicitly set to SMP_CACHE_BYTES.
>> 
>> Replace all such uses of memblock APIs with the 'align' parameter
>explicitly
>> set to SMP_CACHE_BYTES and stop implicit alignment assignment in the
>> memblock internal allocation functions.
>> 
>> For the case when memblock APIs are used via helper functions, e.g.
>like
>> iommu_arena_new_node() in Alpha, the helper functions were detected
>with
>> Coccinelle's help and then manually examined and updated where
>appropriate.
>> 
>> The direct memblock APIs users were updated using the semantic patch
>below:
>
>What is the purpose of this ? It sounds rather counter-intuitive...

Why?
I think it actually more intuitive to explicitly set alignment to SMP_CACHE_BYTES rather than use align = 0 because deeply inside allocator it will be implicitly reset to SMP_CACHE_BYTES...

>Ben.

-- 
Sincerely yours,
Mike.

Re: [PATCH] memblock: stop using implicit alignement to SMP_CACHE_BYTES

[Andrew Morton]

On Fri,  5 Oct 2018 00:07:04 +0300 Mike Rapoport <rppt@linux.vnet.ibm.com> wrote:

> When a memblock allocation APIs are called with align = 0, the alignment is
> implicitly set to SMP_CACHE_BYTES.
> 
> Replace all such uses of memblock APIs with the 'align' parameter explicitly
> set to SMP_CACHE_BYTES and stop implicit alignment assignment in the
> memblock internal allocation functions.
> 
> For the case when memblock APIs are used via helper functions, e.g. like
> iommu_arena_new_node() in Alpha, the helper functions were detected with
> Coccinelle's help and then manually examined and updated where appropriate.
> 
> ...
>
> --- a/mm/memblock.c
> +++ b/mm/memblock.c
> @@ -1298,9 +1298,6 @@ static phys_addr_t __init memblock_alloc_range_nid(phys_addr_t size,
>  {
>  	phys_addr_t found;
>  
> -	if (!align)
> -		align = SMP_CACHE_BYTES;
> -

Can we add a WARN_ON_ONCE(!align) here?  To catch unconverted code
which sneaks in later on.

Re: [PATCH] memblock: stop using implicit alignement to SMP_CACHE_BYTES

[Mike Rapoport]

On Fri, Oct 05, 2018 at 03:19:34PM -0700, Andrew Morton wrote:
> On Fri,  5 Oct 2018 00:07:04 +0300 Mike Rapoport <rppt@linux.vnet.ibm.com> wrote:
> 
> > When a memblock allocation APIs are called with align = 0, the alignment is
> > implicitly set to SMP_CACHE_BYTES.
> > 
> > Replace all such uses of memblock APIs with the 'align' parameter explicitly
> > set to SMP_CACHE_BYTES and stop implicit alignment assignment in the
> > memblock internal allocation functions.
> > 
> > For the case when memblock APIs are used via helper functions, e.g. like
> > iommu_arena_new_node() in Alpha, the helper functions were detected with
> > Coccinelle's help and then manually examined and updated where appropriate.
> > 
> > ...
> >
> > --- a/mm/memblock.c
> > +++ b/mm/memblock.c
> > @@ -1298,9 +1298,6 @@ static phys_addr_t __init memblock_alloc_range_nid(phys_addr_t size,
> >  {
> >  	phys_addr_t found;
> >  
> > -	if (!align)
> > -		align = SMP_CACHE_BYTES;
> > -
> 
> Can we add a WARN_ON_ONCE(!align) here?  To catch unconverted code
> which sneaks in later on.

Here it goes:

>From baec825c58e8bc11371433d3a4b20b2216877a50 Mon Sep 17 00:00:00 2001
From: Mike Rapoport <rppt@linux.vnet.ibm.com>
Date: Mon, 8 Oct 2018 11:22:10 +0300
Subject: [PATCH] memblock: warn if zero alignment was requested

After update of all memblock users to explicitly specify SMP_CACHE_BYTES
alignment rather than use 0, it is still possible that uncovered users
may sneak in. Add a WARN_ON_ONCE for such cases.

Signed-off-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
---
 mm/memblock.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/mm/memblock.c b/mm/memblock.c
index 0bbae56..5fefc70 100644
--- a/mm/memblock.c
+++ b/mm/memblock.c
@@ -1298,6 +1298,9 @@ static phys_addr_t __init memblock_alloc_range_nid(phys_addr_t size,
 {
 	phys_addr_t found;
 
+	if (WARN_ON_ONCE(!align))
+		align = SMP_CACHE_BYTES;
+
 	found = memblock_find_in_range_node(size, align, start, end, nid,
 					    flags);
 	if (found && !memblock_reserve(found, size)) {
@@ -1420,6 +1423,9 @@ static void * __init memblock_alloc_internal(
 	if (WARN_ON_ONCE(slab_is_available()))
 		return kzalloc_node(size, GFP_NOWAIT, nid);
 
+	if (WARN_ON_ONCE(!align))
+		align = SMP_CACHE_BYTES;
+
 	if (max_addr > memblock.current_limit)
 		max_addr = memblock.current_limit;
 again:
-- 
2.7.4


-- 
Sincerely yours,
Mike.