Re: [PATCH 0/5] SLUB debugfs improvements based on stackdepot

[Mike Rapoport <rppt@linux.ibm.com>]

On Tue, Mar 01, 2022 at 10:41:10AM +0100, Vlastimil Babka wrote:
> On 3/1/22 10:21, Mike Rapoport wrote:
> > On Tue, Mar 01, 2022 at 12:38:11AM +0100, Vlastimil Babka wrote:
> >> On 2/28/22 21:01, Mike Rapoport wrote:
> >> > On Mon, Feb 28, 2022 at 08:10:18PM +0100, Vlastimil Babka wrote:
> >> > 
> >> > If stack_depot_init() is called from kmem_cache_init(), there will be a
> >> > confusion what allocator should be used because we use slab_is_available()
> >> > to stop using memblock and start using kmalloc() instead in both
> >> > stack_depot_init() and in memblock.
> >> 
> >> I did check that stack_depot_init() is called from kmem_cache_init()
> >> *before* we make slab_is_available() true, hence assumed that memblock would
> >> be still available at that point and expected no confusion. But seems if
> >> memblock is already beyond memblock_free_all() then it being still available
> >> is just an illusion?
> > 
> > Yeah, it appears it is an illusion :)
> > 
> > I think we have to deal with allocations that happen between
> > memblock_free_all() and slab_is_available() at the memblock level and then
> > figure out the where to put stack_depot_init() and how to allocate memory
> > there.
> > 
> > I believe something like this (untested) patch below addresses the first
> > issue. As for stack_depot_init() I'm still trying to figure out the
> > possible call paths, but it seems we can use stack_depot_early_init() for
> > SLUB debugging case. I'll try to come up with something Really Soon (tm).
> 
> Yeah as you already noticed, we are pursuing an approach to decide on
> calling stack_depot_early_init(), which should be a good way to solve this
> given how special slab is in this case. For memblock I just wanted to point
> out that it could be more robust, your patch below seems to be on the right
> patch. Maybe it just doesn't have to fallback to buddy, which could be
> considered a layering violation, but just return NULL that can be
> immediately recognized as an error?

The layering violation is anyway there for slab_is_available() case, so
adding a __alloc_pages() there will be only consistent.
 
> > diff --git a/include/linux/memblock.h b/include/linux/memblock.h
> > index 50ad19662a32..4ea89d44d22a 100644
> > --- a/include/linux/memblock.h
> > +++ b/include/linux/memblock.h
> > @@ -90,6 +90,7 @@ struct memblock_type {
> >   */
> >  struct memblock {
> >  	bool bottom_up;  /* is bottom up direction? */
> > +	bool mem_freed;
> >  	phys_addr_t current_limit;
> >  	struct memblock_type memory;
> >  	struct memblock_type reserved;
> > diff --git a/mm/memblock.c b/mm/memblock.c
> > index b12a364f2766..60196dc4980e 100644
> > --- a/mm/memblock.c
> > +++ b/mm/memblock.c
> > @@ -120,6 +120,7 @@ struct memblock memblock __initdata_memblock = {
> >  	.reserved.name		= "reserved",
> >  
> >  	.bottom_up		= false,
> > +	.mem_freed		= false,
> >  	.current_limit		= MEMBLOCK_ALLOC_ANYWHERE,
> >  };
> >  
> > @@ -1487,6 +1488,13 @@ static void * __init memblock_alloc_internal(
> >  	if (WARN_ON_ONCE(slab_is_available()))
> >  		return kzalloc_node(size, GFP_NOWAIT, nid);
> >  
> > +	if (memblock.mem_freed) {
> > +		unsigned int order = get_order(size);
> > +
> > +		pr_warn("memblock: allocating from buddy\n");
> > +		return __alloc_pages_node(nid, order, GFP_KERNEL);
> > +	}
> > +
> >  	if (max_addr > memblock.current_limit)
> >  		max_addr = memblock.current_limit;
> >  
> > @@ -2116,6 +2124,7 @@ void __init memblock_free_all(void)
> >  
> >  	pages = free_low_memory_core_early();
> >  	totalram_pages_add(pages);
> > +	memblock.mem_freed = true;
> >  }
> >  
> >  #if defined(CONFIG_DEBUG_FS) && defined(CONFIG_ARCH_KEEP_MEMBLOCK)
> >  

-- 
Sincerely yours,
Mike.