Re: [PATCH RFC 2/5] mm: memcg/percpu: account percpu memory to memory cgroups

Re: [PATCH RFC 2/5] mm: memcg/percpu: account percpu memory to memory cgroups

[Tejun Heo]

On Tue, May 19, 2020 at 01:18:03PM -0700, Roman Gushchin wrote:
> Percpu memory is becoming more and more widely used by various
> subsystems, and the total amount of memory controlled by the percpu
> allocator can make a good part of the total memory.
> 
> As an example, bpf maps can consume a lot of percpu memory,
> and they are created by a user. Also, some cgroup internals
> (e.g. memory controller statistics) can be quite large.
> On a machine with many CPUs and big number of cgroups they
> can consume hundreds of megabytes.
> 
> So the lack of memcg accounting is creating a breach in the memory
> isolation. Similar to the slab memory, percpu memory should be
> accounted by default.
> 
> To implement the perpcu accounting it's possible to take the slab
> memory accounting as a model to follow. Let's introduce two types of
> percpu chunks: root and memcg. What makes memcg chunks different is
> an additional space allocated to store memcg membership information.
> If __GFP_ACCOUNT is passed on allocation, a memcg chunk should be be
> used. If it's possible to charge the corresponding size to the target
> memory cgroup, allocation is performed, and the memcg ownership data
> is recorded. System-wide allocations are performed using root chunks,
> so there is no additional memory overhead.
> 
> To implement a fast reparenting of percpu memory on memcg removal,
> we don't store mem_cgroup pointers directly: instead we use obj_cgroup
> API, introduced for slab accounting.

The overall approach makes sense to me but it'd help to have a high level
comment explaining what's going on and why.

Thanks.

-- 
tejun

Re: [PATCH RFC 2/5] mm: memcg/percpu: account percpu memory to memory cgroups

[Dennis Zhou]

On Tue, May 19, 2020 at 01:18:03PM -0700, Roman Gushchin wrote:
> Percpu memory is becoming more and more widely used by various
> subsystems, and the total amount of memory controlled by the percpu
> allocator can make a good part of the total memory.
> 
> As an example, bpf maps can consume a lot of percpu memory,
> and they are created by a user. Also, some cgroup internals
> (e.g. memory controller statistics) can be quite large.
> On a machine with many CPUs and big number of cgroups they
> can consume hundreds of megabytes.
> 
> So the lack of memcg accounting is creating a breach in the memory
> isolation. Similar to the slab memory, percpu memory should be
> accounted by default.
> 
> To implement the perpcu accounting it's possible to take the slab
> memory accounting as a model to follow. Let's introduce two types of
> percpu chunks: root and memcg. What makes memcg chunks different is
> an additional space allocated to store memcg membership information.
> If __GFP_ACCOUNT is passed on allocation, a memcg chunk should be be
> used. If it's possible to charge the corresponding size to the target
> memory cgroup, allocation is performed, and the memcg ownership data
> is recorded. System-wide allocations are performed using root chunks,
> so there is no additional memory overhead.
> 
> To implement a fast reparenting of percpu memory on memcg removal,
> we don't store mem_cgroup pointers directly: instead we use obj_cgroup
> API, introduced for slab accounting.
> 
> Signed-off-by: Roman Gushchin <guro@fb.com>
> ---
>  mm/percpu-internal.h |  49 +++++++++++-
>  mm/percpu-km.c       |   5 +-
>  mm/percpu-stats.c    |  36 +++++----
>  mm/percpu-vm.c       |   5 +-
>  mm/percpu.c          | 183 +++++++++++++++++++++++++++++++++++++------
>  5 files changed, 237 insertions(+), 41 deletions(-)
> 
> diff --git a/mm/percpu-internal.h b/mm/percpu-internal.h
> index 0468ba500bd4..3ac5613103f7 100644
> --- a/mm/percpu-internal.h
> +++ b/mm/percpu-internal.h
> @@ -5,6 +5,19 @@
>  #include <linux/types.h>
>  #include <linux/percpu.h>
>  
> +/*
> + * There are two chunk types: root and memcg.
> + * Chunks of each type have separate slots list.
> + */

This seems like a good place to add the comment tj asked for. In
addition, do you mind slipping something short into the big block
comment at the top mention this is a thing now too.

> +enum pcpu_chunk_type {
> +	PCPU_CHUNK_ROOT,
> +#ifdef CONFIG_MEMCG_KMEM
> +	PCPU_CHUNK_MEMCG,
> +#endif
> +	PCPU_NR_CHUNK_TYPES,
> +	PCPU_FAIL_ALLOC = PCPU_NR_CHUNK_TYPES
> +};
> +
>  /*
>   * pcpu_block_md is the metadata block struct.
>   * Each chunk's bitmap is split into a number of full blocks.
> @@ -54,6 +67,9 @@ struct pcpu_chunk {
>  	int			end_offset;	/* additional area required to
>  						   have the region end page
>  						   aligned */
> +#ifdef CONFIG_MEMCG_KMEM
> +	struct obj_cgroup	**obj_cgroups;	/* vector of object cgroups */
> +#endif
>  
>  	int			nr_pages;	/* # of pages served by this chunk */
>  	int			nr_populated;	/* # of populated pages */
> @@ -63,7 +79,7 @@ struct pcpu_chunk {
>  
>  extern spinlock_t pcpu_lock;
>  
> -extern struct list_head *pcpu_slot;
> +extern struct list_head *pcpu_chunk_lists;
>  extern int pcpu_nr_slots;
>  extern int pcpu_nr_empty_pop_pages;
>  
> @@ -106,6 +122,37 @@ static inline int pcpu_chunk_map_bits(struct pcpu_chunk *chunk)
>  	return pcpu_nr_pages_to_map_bits(chunk->nr_pages);
>  }
>  
> +#ifdef CONFIG_MEMCG_KMEM
> +static enum pcpu_chunk_type pcpu_chunk_type(struct pcpu_chunk *chunk)
> +{
> +	if (chunk->obj_cgroups)
> +		return PCPU_CHUNK_MEMCG;
> +	return PCPU_CHUNK_ROOT;
> +}
> +
> +static bool pcpu_is_memcg_chunk(enum pcpu_chunk_type chunk_type)
> +{
> +	return chunk_type == PCPU_CHUNK_MEMCG;
> +}
> +
> +#else
> +static enum pcpu_chunk_type pcpu_chunk_type(struct pcpu_chunk *chunk)
> +{
> +	return PCPU_CHUNK_ROOT;
> +}
> +
> +static bool pcpu_is_memcg_chunk(enum pcpu_chunk_type chunk_type)
> +{
> +	return false;
> +}
> +#endif
> +
> +static struct list_head *pcpu_chunk_list(enum pcpu_chunk_type chunk_type)
> +{
> +	return &pcpu_chunk_lists[pcpu_nr_slots *
> +				 pcpu_is_memcg_chunk(chunk_type)];
> +}
> +
>  #ifdef CONFIG_PERCPU_STATS
>  
>  #include <linux/spinlock.h>
> diff --git a/mm/percpu-km.c b/mm/percpu-km.c
> index 20d2b69a13b0..35c9941077ee 100644
> --- a/mm/percpu-km.c
> +++ b/mm/percpu-km.c
> @@ -44,7 +44,8 @@ static void pcpu_depopulate_chunk(struct pcpu_chunk *chunk,
>  	/* nada */
>  }
>  
> -static struct pcpu_chunk *pcpu_create_chunk(gfp_t gfp)
> +static struct pcpu_chunk *pcpu_create_chunk(enum pcpu_chunk_type type,
> +					    gfp_t gfp)
>  {
>  	const int nr_pages = pcpu_group_sizes[0] >> PAGE_SHIFT;
>  	struct pcpu_chunk *chunk;
> @@ -52,7 +53,7 @@ static struct pcpu_chunk *pcpu_create_chunk(gfp_t gfp)
>  	unsigned long flags;
>  	int i;
>  
> -	chunk = pcpu_alloc_chunk(gfp);
> +	chunk = pcpu_alloc_chunk(type, gfp);
>  	if (!chunk)
>  		return NULL;
>  
> diff --git a/mm/percpu-stats.c b/mm/percpu-stats.c
> index 32558063c3f9..c8400a2adbc2 100644
> --- a/mm/percpu-stats.c
> +++ b/mm/percpu-stats.c
> @@ -34,11 +34,15 @@ static int find_max_nr_alloc(void)
>  {
>  	struct pcpu_chunk *chunk;
>  	int slot, max_nr_alloc;
> +	enum pcpu_chunk_type type;
>  
>  	max_nr_alloc = 0;
> -	for (slot = 0; slot < pcpu_nr_slots; slot++)
> -		list_for_each_entry(chunk, &pcpu_slot[slot], list)
> -			max_nr_alloc = max(max_nr_alloc, chunk->nr_alloc);
> +	for (type = 0; type < PCPU_NR_CHUNK_TYPES; type++)
> +		for (slot = 0; slot < pcpu_nr_slots; slot++)
> +			list_for_each_entry(chunk, &pcpu_chunk_list(type)[slot],
> +					    list)
> +				max_nr_alloc = max(max_nr_alloc,
> +						   chunk->nr_alloc);
>  
>  	return max_nr_alloc;
>  }
> @@ -129,6 +133,9 @@ static void chunk_map_stats(struct seq_file *m, struct pcpu_chunk *chunk,
>  	P("cur_min_alloc", cur_min_alloc);
>  	P("cur_med_alloc", cur_med_alloc);
>  	P("cur_max_alloc", cur_max_alloc);
> +#ifdef CONFIG_MEMCG_KMEM
> +	P("memcg_aware", pcpu_is_memcg_chunk(pcpu_chunk_type(chunk)));
> +#endif
>  	seq_putc(m, '\n');
>  }
>  
> @@ -137,6 +144,7 @@ static int percpu_stats_show(struct seq_file *m, void *v)
>  	struct pcpu_chunk *chunk;
>  	int slot, max_nr_alloc;
>  	int *buffer;
> +	enum pcpu_chunk_type type;
>  
>  alloc_buffer:
>  	spin_lock_irq(&pcpu_lock);
> @@ -202,18 +210,18 @@ static int percpu_stats_show(struct seq_file *m, void *v)
>  		chunk_map_stats(m, pcpu_reserved_chunk, buffer);
>  	}
>  
> -	for (slot = 0; slot < pcpu_nr_slots; slot++) {
> -		list_for_each_entry(chunk, &pcpu_slot[slot], list) {
> -			if (chunk == pcpu_first_chunk) {
> -				seq_puts(m, "Chunk: <- First Chunk\n");
> -				chunk_map_stats(m, chunk, buffer);
> -
> -
> -			} else {
> -				seq_puts(m, "Chunk:\n");
> -				chunk_map_stats(m, chunk, buffer);
> +	for (type = 0; type < PCPU_NR_CHUNK_TYPES; type++) {
> +		for (slot = 0; slot < pcpu_nr_slots; slot++) {
> +			list_for_each_entry(chunk, &pcpu_chunk_list(type)[slot],
> +					    list) {
> +				if (chunk == pcpu_first_chunk) {
> +					seq_puts(m, "Chunk: <- First Chunk\n");
> +					chunk_map_stats(m, chunk, buffer);
> +				} else {
> +					seq_puts(m, "Chunk:\n");
> +					chunk_map_stats(m, chunk, buffer);
> +				}
>  			}
> -
>  		}
>  	}
>  
> diff --git a/mm/percpu-vm.c b/mm/percpu-vm.c
> index a2b395acef89..e46f7a6917f9 100644
> --- a/mm/percpu-vm.c
> +++ b/mm/percpu-vm.c
> @@ -328,12 +328,13 @@ static void pcpu_depopulate_chunk(struct pcpu_chunk *chunk,
>  	pcpu_free_pages(chunk, pages, page_start, page_end);
>  }
>  
> -static struct pcpu_chunk *pcpu_create_chunk(gfp_t gfp)
> +static struct pcpu_chunk *pcpu_create_chunk(enum pcpu_chunk_type type,
> +					    gfp_t gfp)
>  {
>  	struct pcpu_chunk *chunk;
>  	struct vm_struct **vms;
>  
> -	chunk = pcpu_alloc_chunk(gfp);
> +	chunk = pcpu_alloc_chunk(type, gfp);
>  	if (!chunk)
>  		return NULL;
>  
> diff --git a/mm/percpu.c b/mm/percpu.c
> index aa36b78d45a6..4615a0a809b8 100644
> --- a/mm/percpu.c
> +++ b/mm/percpu.c
> @@ -81,6 +81,7 @@
>  #include <linux/kmemleak.h>
>  #include <linux/sched.h>
>  #include <linux/sched/mm.h>
> +#include <linux/memcontrol.h>
>  
>  #include <asm/cacheflush.h>
>  #include <asm/sections.h>
> @@ -160,7 +161,7 @@ struct pcpu_chunk *pcpu_reserved_chunk __ro_after_init;
>  DEFINE_SPINLOCK(pcpu_lock);	/* all internal data structures */
>  static DEFINE_MUTEX(pcpu_alloc_mutex);	/* chunk create/destroy, [de]pop, map ext */
>  
> -struct list_head *pcpu_slot __ro_after_init; /* chunk list slots */
> +struct list_head *pcpu_chunk_lists __ro_after_init; /* chunk list slots */
>  
>  /* chunks which need their map areas extended, protected by pcpu_lock */
>  static LIST_HEAD(pcpu_map_extend_chunks);
> @@ -500,6 +501,9 @@ static void __pcpu_chunk_move(struct pcpu_chunk *chunk, int slot,
>  			      bool move_front)
>  {
>  	if (chunk != pcpu_reserved_chunk) {
> +		struct list_head *pcpu_slot;
> +
> +		pcpu_slot = pcpu_chunk_list(pcpu_chunk_type(chunk));
>  		if (move_front)
>  			list_move(&chunk->list, &pcpu_slot[slot]);
>  		else
> @@ -1341,6 +1345,10 @@ static struct pcpu_chunk * __init pcpu_alloc_first_chunk(unsigned long tmp_addr,
>  		panic("%s: Failed to allocate %zu bytes\n", __func__,
>  		      alloc_size);
>  
> +#ifdef CONFIG_MEMCG_KMEM
> +	/* first chunk isn't memcg-aware */
> +	chunk->obj_cgroups = NULL;
> +#endif
>  	pcpu_init_md_blocks(chunk);
>  
>  	/* manage populated page bitmap */
> @@ -1380,7 +1388,7 @@ static struct pcpu_chunk * __init pcpu_alloc_first_chunk(unsigned long tmp_addr,
>  	return chunk;
>  }
>  
> -static struct pcpu_chunk *pcpu_alloc_chunk(gfp_t gfp)
> +static struct pcpu_chunk *pcpu_alloc_chunk(enum pcpu_chunk_type type, gfp_t gfp)
>  {
>  	struct pcpu_chunk *chunk;
>  	int region_bits;
> @@ -1408,6 +1416,16 @@ static struct pcpu_chunk *pcpu_alloc_chunk(gfp_t gfp)
>  	if (!chunk->md_blocks)
>  		goto md_blocks_fail;
>  
> +#ifdef CONFIG_MEMCG_KMEM
> +	if (pcpu_is_memcg_chunk(type)) {
> +		chunk->obj_cgroups =
> +			pcpu_mem_zalloc(pcpu_chunk_map_bits(chunk) *
> +					sizeof(struct obj_cgroup *), gfp);
> +		if (!chunk->obj_cgroups)
> +			goto objcg_fail;
> +	}
> +#endif
> +
>  	pcpu_init_md_blocks(chunk);
>  
>  	/* init metadata */
> @@ -1415,6 +1433,8 @@ static struct pcpu_chunk *pcpu_alloc_chunk(gfp_t gfp)
>  
>  	return chunk;
>  
> +objcg_fail:
> +	pcpu_mem_free(chunk->md_blocks);
>  md_blocks_fail:
>  	pcpu_mem_free(chunk->bound_map);
>  bound_map_fail:
> @@ -1429,6 +1449,9 @@ static void pcpu_free_chunk(struct pcpu_chunk *chunk)
>  {
>  	if (!chunk)
>  		return;
> +#ifdef CONFIG_MEMCG_KMEM
> +	pcpu_mem_free(chunk->obj_cgroups);
> +#endif
>  	pcpu_mem_free(chunk->md_blocks);
>  	pcpu_mem_free(chunk->bound_map);
>  	pcpu_mem_free(chunk->alloc_map);
> @@ -1505,7 +1528,8 @@ static int pcpu_populate_chunk(struct pcpu_chunk *chunk,
>  			       int page_start, int page_end, gfp_t gfp);
>  static void pcpu_depopulate_chunk(struct pcpu_chunk *chunk,
>  				  int page_start, int page_end);
> -static struct pcpu_chunk *pcpu_create_chunk(gfp_t gfp);
> +static struct pcpu_chunk *pcpu_create_chunk(enum pcpu_chunk_type type,
> +					    gfp_t gfp);
>  static void pcpu_destroy_chunk(struct pcpu_chunk *chunk);
>  static struct page *pcpu_addr_to_page(void *addr);
>  static int __init pcpu_verify_alloc_info(const struct pcpu_alloc_info *ai);
> @@ -1547,6 +1571,77 @@ static struct pcpu_chunk *pcpu_chunk_addr_search(void *addr)
>  	return pcpu_get_page_chunk(pcpu_addr_to_page(addr));
>  }
>  
> +#ifdef CONFIG_MEMCG_KMEM
> +static enum pcpu_chunk_type pcpu_memcg_pre_alloc_hook(size_t size, gfp_t gfp,
> +						     struct obj_cgroup **objcgp)
> +{
> +	struct obj_cgroup *objcg;
> +
> +	if (!memcg_kmem_enabled() || !(gfp & __GFP_ACCOUNT) ||
> +	    memcg_kmem_bypass())
> +		return PCPU_CHUNK_ROOT;
> +
> +	objcg = get_obj_cgroup_from_current();
> +	if (!objcg)
> +		return PCPU_CHUNK_ROOT;
> +
> +	if (obj_cgroup_charge(objcg, gfp, size * num_possible_cpus())) {
> +		obj_cgroup_put(objcg);
> +		return PCPU_FAIL_ALLOC;
> +	}
> +
> +	*objcgp = objcg;
> +	return PCPU_CHUNK_MEMCG;
> +}
> +
> +static void pcpu_memcg_post_alloc_hook(struct obj_cgroup *objcg,
> +				       struct pcpu_chunk *chunk, int off,
> +				       size_t size)
> +{
> +	if (!objcg)
> +		return;
> +
> +	if (chunk) {
> +		chunk->obj_cgroups[off >> PCPU_MIN_ALLOC_SHIFT] = objcg;
> +	} else {
> +		obj_cgroup_uncharge(objcg, size * num_possible_cpus());
> +		obj_cgroup_put(objcg);
> +	}
> +}
> +
> +static void pcpu_memcg_free_hook(struct pcpu_chunk *chunk, int off, size_t size)
> +{
> +	struct obj_cgroup *objcg;
> +
> +	if (!pcpu_is_memcg_chunk(pcpu_chunk_type(chunk)))
> +		return;
> +
> +	objcg = chunk->obj_cgroups[off >> PCPU_MIN_ALLOC_SHIFT];
> +	chunk->obj_cgroups[off >> PCPU_MIN_ALLOC_SHIFT] = NULL;
> +
> +	obj_cgroup_uncharge(objcg, size * num_possible_cpus());
> +
> +	obj_cgroup_put(objcg);
> +}
> +
> +#else /* CONFIG_MEMCG_KMEM */
> +static enum pcpu_chunk_type pcpu_memcg_pre_alloc_hook(size_t size, gfp_t gfp,
> +						     struct mem_cgroup **memcgp)
> +{
> +	return PCPU_CHUNK_ROOT;
> +}
> +
> +static void pcpu_memcg_post_alloc_hook(struct mem_cgroup *memcg,
> +				       struct pcpu_chunk *chunk, int off,
> +				       size_t size)
> +{
> +}
> +
> +static void pcpu_memcg_free_hook(struct pcpu_chunk *chunk, int off, size_t size)
> +{
> +}
> +#endif /* CONFIG_MEMCG_KMEM */
> +
>  /**
>   * pcpu_alloc - the percpu allocator
>   * @size: size of area to allocate in bytes
> @@ -1565,9 +1660,14 @@ static struct pcpu_chunk *pcpu_chunk_addr_search(void *addr)
>  static void __percpu *pcpu_alloc(size_t size, size_t align, bool reserved,
>  				 gfp_t gfp)
>  {
> -	gfp_t pcpu_gfp;
> -	bool is_atomic;
> -	bool do_warn;
> +	/* whitelisted flags that can be passed to the backing allocators */
> +	gfp_t pcpu_gfp = gfp & (GFP_KERNEL | __GFP_NORETRY | __GFP_NOWARN |
> +				__GFP_ACCOUNT);
> +	bool is_atomic = (gfp & GFP_KERNEL) != GFP_KERNEL;
> +	bool do_warn = !(gfp & __GFP_NOWARN);
> +	enum pcpu_chunk_type type;
> +	struct list_head *pcpu_slot;
> +	struct obj_cgroup *objcg = NULL;

First, this collides w/ another patch that went in, 28307d938fb2.

Second, pcpu_gfp is to limit the flags that actually make it to the
backing allocator. I don't believe we want to pass __GFP_ACCOUNT to the
backing allocator right? This would charge a whole page in addition to
the hooks (should we need to allocate).  The pcpu_memcg_*_hook()s can
use the passed gfp directly.

>  	static int warn_limit = 10;
>  	struct pcpu_chunk *chunk, *next;
>  	const char *err;
> @@ -1602,16 +1702,23 @@ static void __percpu *pcpu_alloc(size_t size, size_t align, bool reserved,
>  		return NULL;
>  	}
>  
> +	type = pcpu_memcg_pre_alloc_hook(size, gfp, &objcg);

^ as you're doing here using gfp not pcpu_gfp.

> +	if (unlikely(type == PCPU_FAIL_ALLOC))
> +		return NULL;
> +	pcpu_slot = pcpu_chunk_list(type);
> +
>  	if (!is_atomic) {
>  		/*
>  		 * pcpu_balance_workfn() allocates memory under this mutex,
>  		 * and it may wait for memory reclaim. Allow current task
>  		 * to become OOM victim, in case of memory pressure.
>  		 */
> -		if (gfp & __GFP_NOFAIL)
> +		if (gfp & __GFP_NOFAIL) {
>  			mutex_lock(&pcpu_alloc_mutex);
> -		else if (mutex_lock_killable(&pcpu_alloc_mutex))
> +		} else if (mutex_lock_killable(&pcpu_alloc_mutex)) {
> +			pcpu_memcg_post_alloc_hook(objcg, NULL, 0, size);
>  			return NULL;
> +		}
>  	}
>  
>  	spin_lock_irqsave(&pcpu_lock, flags);
> @@ -1637,7 +1744,8 @@ static void __percpu *pcpu_alloc(size_t size, size_t align, bool reserved,
>  restart:
>  	/* search through normal chunks */
>  	for (slot = pcpu_size_to_slot(size); slot < pcpu_nr_slots; slot++) {
> -		list_for_each_entry_safe(chunk, next, &pcpu_slot[slot], list) {
> +		list_for_each_entry_safe(chunk, next, &pcpu_slot[slot],
> +					 list) {
>  			off = pcpu_find_block_fit(chunk, bits, bit_align,
>  						  is_atomic);
>  			if (off < 0) {
> @@ -1666,7 +1774,7 @@ static void __percpu *pcpu_alloc(size_t size, size_t align, bool reserved,
>  	}
>  
>  	if (list_empty(&pcpu_slot[pcpu_nr_slots - 1])) {
> -		chunk = pcpu_create_chunk(pcpu_gfp);
> +		chunk = pcpu_create_chunk(type, pcpu_gfp);
>  		if (!chunk) {
>  			err = "failed to allocate new chunk";
>  			goto fail;
> @@ -1723,6 +1831,8 @@ static void __percpu *pcpu_alloc(size_t size, size_t align, bool reserved,
>  	trace_percpu_alloc_percpu(reserved, is_atomic, size, align,
>  			chunk->base_addr, off, ptr);
>  
> +	pcpu_memcg_post_alloc_hook(objcg, chunk, off, size);
> +
>  	return ptr;
>  
>  fail_unlock:
> @@ -1744,6 +1854,9 @@ static void __percpu *pcpu_alloc(size_t size, size_t align, bool reserved,
>  	} else {
>  		mutex_unlock(&pcpu_alloc_mutex);
>  	}
> +
> +	pcpu_memcg_post_alloc_hook(objcg, NULL, 0, size);
> +
>  	return NULL;
>  }
>  
> @@ -1803,8 +1916,8 @@ void __percpu *__alloc_reserved_percpu(size_t size, size_t align)
>  }
>  
>  /**
> - * pcpu_balance_workfn - manage the amount of free chunks and populated pages
> - * @work: unused
> + * __pcpu_balance_workfn - manage the amount of free chunks and populated pages
> + * @type: chunk type
>   *
>   * Reclaim all fully free chunks except for the first one.  This is also
>   * responsible for maintaining the pool of empty populated pages.  However,
> @@ -1813,11 +1926,12 @@ void __percpu *__alloc_reserved_percpu(size_t size, size_t align)
>   * allocation causes the failure as it is possible that requests can be
>   * serviced from already backed regions.
>   */
> -static void pcpu_balance_workfn(struct work_struct *work)
> +static void __pcpu_balance_workfn(enum pcpu_chunk_type type)
>  {
>  	/* gfp flags passed to underlying allocators */
>  	const gfp_t gfp = GFP_KERNEL | __GFP_NORETRY | __GFP_NOWARN;
>  	LIST_HEAD(to_free);
> +	struct list_head *pcpu_slot = pcpu_chunk_list(type);
>  	struct list_head *free_head = &pcpu_slot[pcpu_nr_slots - 1];
>  	struct pcpu_chunk *chunk, *next;
>  	int slot, nr_to_pop, ret;
> @@ -1915,7 +2029,7 @@ static void pcpu_balance_workfn(struct work_struct *work)
>  
>  	if (nr_to_pop) {
>  		/* ran out of chunks to populate, create a new one and retry */
> -		chunk = pcpu_create_chunk(gfp);
> +		chunk = pcpu_create_chunk(type, gfp);
>  		if (chunk) {
>  			spin_lock_irq(&pcpu_lock);
>  			pcpu_chunk_relocate(chunk, -1);
> @@ -1927,6 +2041,20 @@ static void pcpu_balance_workfn(struct work_struct *work)
>  	mutex_unlock(&pcpu_alloc_mutex);
>  }
>  
> +/**
> + * pcpu_balance_workfn - manage the amount of free chunks and populated pages
> + * @work: unused
> + *
> + * Call __pcpu_balance_workfn() for each chunk type.
> + */
> +static void pcpu_balance_workfn(struct work_struct *work)
> +{
> +	enum pcpu_chunk_type type;
> +
> +	for (type = 0; type < PCPU_NR_CHUNK_TYPES; type++)
> +		__pcpu_balance_workfn(type);
> +}
> +
>  /**
>   * free_percpu - free percpu area
>   * @ptr: pointer to area to free
> @@ -1941,8 +2069,9 @@ void free_percpu(void __percpu *ptr)
>  	void *addr;
>  	struct pcpu_chunk *chunk;
>  	unsigned long flags;
> -	int off;
> +	int size, off;
>  	bool need_balance = false;
> +	struct list_head *pcpu_slot;
>  
>  	if (!ptr)
>  		return;
> @@ -1956,7 +2085,11 @@ void free_percpu(void __percpu *ptr)
>  	chunk = pcpu_chunk_addr_search(addr);
>  	off = addr - chunk->base_addr;
>  
> -	pcpu_free_area(chunk, off);
> +	size = pcpu_free_area(chunk, off);
> +
> +	pcpu_slot = pcpu_chunk_list(pcpu_chunk_type(chunk));
> +
> +	pcpu_memcg_free_hook(chunk, off, size);
>  
>  	/* if there are more than one fully free chunks, wake up grim reaper */
>  	if (chunk->free_bytes == pcpu_unit_size) {
> @@ -2267,6 +2400,7 @@ void __init pcpu_setup_first_chunk(const struct pcpu_alloc_info *ai,
>  	int map_size;
>  	unsigned long tmp_addr;
>  	size_t alloc_size;
> +	enum pcpu_chunk_type type;
>  
>  #define PCPU_SETUP_BUG_ON(cond)	do {					\
>  	if (unlikely(cond)) {						\
> @@ -2384,13 +2518,18 @@ void __init pcpu_setup_first_chunk(const struct pcpu_alloc_info *ai,
>  	 * empty chunks.
>  	 */
>  	pcpu_nr_slots = __pcpu_size_to_slot(pcpu_unit_size) + 2;
> -	pcpu_slot = memblock_alloc(pcpu_nr_slots * sizeof(pcpu_slot[0]),
> -				   SMP_CACHE_BYTES);
> -	if (!pcpu_slot)
> +	pcpu_chunk_lists = memblock_alloc(pcpu_nr_slots *
> +					  sizeof(pcpu_chunk_lists[0]) *
> +					  PCPU_NR_CHUNK_TYPES,
> +					  SMP_CACHE_BYTES);
> +	if (!pcpu_chunk_lists)
>  		panic("%s: Failed to allocate %zu bytes\n", __func__,
> -		      pcpu_nr_slots * sizeof(pcpu_slot[0]));
> -	for (i = 0; i < pcpu_nr_slots; i++)
> -		INIT_LIST_HEAD(&pcpu_slot[i]);
> +		      pcpu_nr_slots * sizeof(pcpu_chunk_lists[0]) *
> +		      PCPU_NR_CHUNK_TYPES);
> +
> +	for (type = 0; type < PCPU_NR_CHUNK_TYPES; type++)
> +		for (i = 0; i < pcpu_nr_slots; i++)
> +			INIT_LIST_HEAD(&pcpu_chunk_list(type)[i]);
>  
>  	/*
>  	 * The end of the static region needs to be aligned with the
> -- 
> 2.25.4
> 

Thanks this looks pretty good to me.

Thanks,
Dennis