Date:   Mon, 29 Nov 2021 17:45:44 -0500
From:   Dennis Zhou <dennis@kernel.org>
To:     Kefeng Wang <wangkefeng.wang@huawei.com>
Cc:     akpm@linux-foundation.org, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, tj@kernel.org, gregkh@linuxfoundation.org,
        cl@linux.com, catalin.marinas@arm.com, will@kernel.org,
        tsbogend@alpha.franken.de, mpe@ellerman.id.au,
        benh@kernel.crashing.org, paulus@samba.org,
        paul.walmsley@sifive.com, palmer@dabbelt.com,
        aou@eecs.berkeley.edu, davem@davemloft.net, tglx@linutronix.de,
        mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com,
        hpa@zytor.com, linux-arm-kernel@lists.infradead.org,
        linux-ia64@vger.kernel.org, linux-mips@vger.kernel.org,
        linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org,
        sparclinux@vger.kernel.org, x86@kernel.org
Subject: Re: [PATCH RFC 3/4] mm: percpu: Add generic pcpu_fc_alloc/free
 funciton
Message-ID: <YaVYGCB+I7QLZo0+@fedora>
References: <20211121093557.139034-1-wangkefeng.wang@huawei.com>
 <20211121093557.139034-4-wangkefeng.wang@huawei.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
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In-Reply-To: <20211121093557.139034-4-wangkefeng.wang@huawei.com>
Precedence: bulk

On Sun, Nov 21, 2021 at 05:35:56PM +0800, Kefeng Wang wrote:
> With previous patch, we could add a generic pcpu first chunk
> allocation and free function to cleanup the duplicated definations
> on each architecture.
> 
> Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
> ---
>  arch/mips/mm/init.c            | 16 +--------
>  arch/powerpc/kernel/setup_64.c | 51 ++------------------------
>  arch/sparc/kernel/smp_64.c     | 50 +-------------------------
>  arch/x86/kernel/setup_percpu.c | 59 +-----------------------------
>  drivers/base/arch_numa.c       | 19 +---------
>  include/linux/percpu.h         |  9 +----
>  mm/percpu.c                    | 66 ++++++++++++++++++----------------
>  7 files changed, 42 insertions(+), 228 deletions(-)
> 
> diff --git a/arch/mips/mm/init.c b/arch/mips/mm/init.c
> index ebbf6923532c..5a8002839550 100644
> --- a/arch/mips/mm/init.c
> +++ b/arch/mips/mm/init.c
> @@ -524,19 +524,6 @@ static int __init pcpu_cpu_to_node(int cpu)
>  	return cpu_to_node(cpu);
>  }
>  
> -static void * __init pcpu_fc_alloc(unsigned int cpu, size_t size, size_t align,
> -				   pcpu_fc_cpu_to_node_fn_t cpu_to_nd_fn)
> -{
> -	return memblock_alloc_try_nid(size, align, __pa(MAX_DMA_ADDRESS),
> -				      MEMBLOCK_ALLOC_ACCESSIBLE,
> -				      cpu_to_nd_fun(cpu));
> -}
> -
> -static void __init pcpu_fc_free(void *ptr, size_t size)
> -{
> -	memblock_free(ptr, size);
> -}
> -
>  void __init setup_per_cpu_areas(void)
>  {
>  	unsigned long delta;
> @@ -550,8 +537,7 @@ void __init setup_per_cpu_areas(void)
>  	rc = pcpu_embed_first_chunk(PERCPU_MODULE_RESERVE,
>  				    PERCPU_DYNAMIC_RESERVE, PAGE_SIZE,
>  				    pcpu_cpu_distance,
> -				    pcpu_cpu_to_node,
> -				    pcpu_fc_alloc, pcpu_fc_free);
> +				    pcpu_cpu_to_node);
>  	if (rc < 0)
>  		panic("Failed to initialize percpu areas.");
>  
> diff --git a/arch/powerpc/kernel/setup_64.c b/arch/powerpc/kernel/setup_64.c
> index 9a5609c821df..364b1567f822 100644
> --- a/arch/powerpc/kernel/setup_64.c
> +++ b/arch/powerpc/kernel/setup_64.c
> @@ -777,50 +777,6 @@ static __init int pcpu_cpu_to_node(int cpu)
>  	return IS_ENABLED(CONFIG_NUMA) ? early_cpu_to_node(cpu) : NUMA_NO_NODE;
>  }
>  
> -/**
> - * pcpu_alloc_bootmem - NUMA friendly alloc_bootmem wrapper for percpu
> - * @cpu: cpu to allocate for
> - * @size: size allocation in bytes
> - * @align: alignment
> - *
> - * Allocate @size bytes aligned at @align for cpu @cpu.  This wrapper
> - * does the right thing for NUMA regardless of the current
> - * configuration.
> - *
> - * RETURNS:
> - * Pointer to the allocated area on success, NULL on failure.
> - */
> -static void * __init pcpu_alloc_bootmem(unsigned int cpu, size_t size, size_t align,
> -					pcpu_fc_cpu_to_node_fn_t cpu_to_nd_fn)
> -{
> -	const unsigned long goal = __pa(MAX_DMA_ADDRESS);
> -#ifdef CONFIG_NUMA
> -	int node = cpu_to_nd_fun(cpu);
> -	void *ptr;
> -
> -	if (!node_online(node) || !NODE_DATA(node)) {
> -		ptr = memblock_alloc_from(size, align, goal);
> -		pr_info("cpu %d has no node %d or node-local memory\n",
> -			cpu, node);
> -		pr_debug("per cpu data for cpu%d %lu bytes at %016lx\n",
> -			 cpu, size, __pa(ptr));
> -	} else {
> -		ptr = memblock_alloc_try_nid(size, align, goal,
> -					     MEMBLOCK_ALLOC_ACCESSIBLE, node);
> -		pr_debug("per cpu data for cpu%d %lu bytes on node%d at "
> -			 "%016lx\n", cpu, size, node, __pa(ptr));
> -	}
> -	return ptr;
> -#else
> -	return memblock_alloc_from(size, align, goal);
> -#endif
> -}
> -
> -static void __init pcpu_free_bootmem(void *ptr, size_t size)
> -{
> -	memblock_free(ptr, size);
> -}
> -
>  static int pcpu_cpu_distance(unsigned int from, unsigned int to)
>  {
>  	if (early_cpu_to_node(from) == early_cpu_to_node(to))
> @@ -897,8 +853,7 @@ void __init setup_per_cpu_areas(void)
>  
>  	if (pcpu_chosen_fc != PCPU_FC_PAGE) {
>  		rc = pcpu_embed_first_chunk(0, dyn_size, atom_size, pcpu_cpu_distance,
> -					    pcpu_cpu_to_node,
> -					    pcpu_alloc_bootmem, pcpu_free_bootmem);
> +					    pcpu_cpu_to_node);
>  		if (rc)
>  			pr_warn("PERCPU: %s allocator failed (%d), "
>  				"falling back to page size\n",
> @@ -906,9 +861,7 @@ void __init setup_per_cpu_areas(void)
>  	}
>  
>  	if (rc < 0)
> -		rc = pcpu_page_first_chunk(0, pcpu_alloc_bootmem, pcpu_free_bootmem,
> -					   pcpu_cpu_to_node,
> -					   pcpu_populate_pte);
> +		rc = pcpu_page_first_chunk(0, pcpu_cpu_to_node, pcpu_populate_pte);
>  	if (rc < 0)
>  		panic("cannot initialize percpu area (err=%d)", rc);
>  
> diff --git a/arch/sparc/kernel/smp_64.c b/arch/sparc/kernel/smp_64.c
> index 026aa3ccbc30..198dadddb75d 100644
> --- a/arch/sparc/kernel/smp_64.c
> +++ b/arch/sparc/kernel/smp_64.c
> @@ -1526,50 +1526,6 @@ void smp_send_stop(void)
>  		smp_call_function(stop_this_cpu, NULL, 0);
>  }
>  
> -/**
> - * pcpu_alloc_bootmem - NUMA friendly alloc_bootmem wrapper for percpu
> - * @cpu: cpu to allocate for
> - * @size: size allocation in bytes
> - * @align: alignment
> - *
> - * Allocate @size bytes aligned at @align for cpu @cpu.  This wrapper
> - * does the right thing for NUMA regardless of the current
> - * configuration.
> - *
> - * RETURNS:
> - * Pointer to the allocated area on success, NULL on failure.
> - */
> -static void * __init pcpu_alloc_bootmem(unsigned int cpu, size_t size, size_t align,
> -					pcpu_fc_cpu_to_node_fn_t cpu_to_nd_fn)
> -{
> -	const unsigned long goal = __pa(MAX_DMA_ADDRESS);
> -#ifdef CONFIG_NUMA
> -	int node = cpu_to_nd_fn(cpu);
> -	void *ptr;
> -
> -	if (!node_online(node) || !NODE_DATA(node)) {
> -		ptr = memblock_alloc_from(size, align, goal);
> -		pr_info("cpu %d has no node %d or node-local memory\n",
> -			cpu, node);
> -		pr_debug("per cpu data for cpu%d %lu bytes at %016lx\n",
> -			 cpu, size, __pa(ptr));
> -	} else {
> -		ptr = memblock_alloc_try_nid(size, align, goal,
> -					     MEMBLOCK_ALLOC_ACCESSIBLE, node);
> -		pr_debug("per cpu data for cpu%d %lu bytes on node%d at "
> -			 "%016lx\n", cpu, size, node, __pa(ptr));
> -	}
> -	return ptr;
> -#else
> -	return memblock_alloc_from(size, align, goal);
> -#endif
> -}
> -
> -static void __init pcpu_free_bootmem(void *ptr, size_t size)
> -{
> -	memblock_free(ptr, size);
> -}
> -
>  static int __init pcpu_cpu_distance(unsigned int from, unsigned int to)
>  {
>  	if (cpu_to_node(from) == cpu_to_node(to))
> @@ -1641,9 +1597,7 @@ void __init setup_per_cpu_areas(void)
>  		rc = pcpu_embed_first_chunk(PERCPU_MODULE_RESERVE,
>  					    PERCPU_DYNAMIC_RESERVE, 4 << 20,
>  					    pcpu_cpu_distance,
> -					    cpu_to_node,
> -					    pcpu_alloc_bootmem,
> -					    pcpu_free_bootmem);
> +					    cpu_to_node);
>  		if (rc)
>  			pr_warn("PERCPU: %s allocator failed (%d), "
>  				"falling back to page size\n",
> @@ -1651,8 +1605,6 @@ void __init setup_per_cpu_areas(void)
>  	}
>  	if (rc < 0)
>  		rc = pcpu_page_first_chunk(PERCPU_MODULE_RESERVE,
> -					   pcpu_alloc_bootmem,
> -					   pcpu_free_bootmem,
>  					   cpu_to_node,
>  					   pcpu_populate_pte);
>  	if (rc < 0)
> diff --git a/arch/x86/kernel/setup_percpu.c b/arch/x86/kernel/setup_percpu.c
> index bba4fa174a16..cd672bd46241 100644
> --- a/arch/x86/kernel/setup_percpu.c
> +++ b/arch/x86/kernel/setup_percpu.c
> @@ -84,61 +84,6 @@ static bool __init pcpu_need_numa(void)
>  }
>  #endif
>  
> -/**
> - * pcpu_alloc_bootmem - NUMA friendly alloc_bootmem wrapper for percpu
> - * @cpu: cpu to allocate for
> - * @size: size allocation in bytes
> - * @align: alignment
> - *
> - * Allocate @size bytes aligned at @align for cpu @cpu.  This wrapper
> - * does the right thing for NUMA regardless of the current
> - * configuration.
> - *
> - * RETURNS:
> - * Pointer to the allocated area on success, NULL on failure.
> - */
> -static void * __init pcpu_alloc_bootmem(unsigned int cpu, unsigned long size, unsigned long align,
> -					pcpu_fc_cpu_to_node_fn_t cpu_to_nd_fn)
> -{
> -	const unsigned long goal = __pa(MAX_DMA_ADDRESS);
> -#ifdef CONFIG_NUMA
> -	int node = cpu_to_nd_fn(cpu);
> -	void *ptr;
> -
> -	if (!node_online(node) || !NODE_DATA(node)) {
> -		ptr = memblock_alloc_from(size, align, goal);
> -		pr_info("cpu %d has no node %d or node-local memory\n",
> -			cpu, node);
> -		pr_debug("per cpu data for cpu%d %lu bytes at %016lx\n",
> -			 cpu, size, __pa(ptr));
> -	} else {
> -		ptr = memblock_alloc_try_nid(size, align, goal,
> -					     MEMBLOCK_ALLOC_ACCESSIBLE,
> -					     node);
> -
> -		pr_debug("per cpu data for cpu%d %lu bytes on node%d at %016lx\n",
> -			 cpu, size, node, __pa(ptr));
> -	}
> -	return ptr;
> -#else
> -	return memblock_alloc_from(size, align, goal);
> -#endif
> -}
> -
> -/*
> - * Helpers for first chunk memory allocation
> - */
> -static void * __init pcpu_fc_alloc(unsigned int cpu, size_t size, size_t align,
> -				   pcpu_fc_cpu_to_node_fn_t cpu_to_nd_fn)
> -{
> -	return pcpu_alloc_bootmem(cpu, size, align, cpu_to_nd_fn);
> -}
> -
> -static void __init pcpu_fc_free(void *ptr, size_t size)
> -{
> -	memblock_free(ptr, size);
> -}
> -
>  static int __init pcpu_cpu_distance(unsigned int from, unsigned int to)
>  {
>  #ifdef CONFIG_NUMA
> @@ -211,15 +156,13 @@ void __init setup_per_cpu_areas(void)
>  		rc = pcpu_embed_first_chunk(PERCPU_FIRST_CHUNK_RESERVE,
>  					    dyn_size, atom_size,
>  					    pcpu_cpu_distance,
> -					    pcpu_cpu_to_node,
> -					    pcpu_fc_alloc, pcpu_fc_free);
> +					    pcpu_cpu_to_node);
>  		if (rc < 0)
>  			pr_warn("%s allocator failed (%d), falling back to page size\n",
>  				pcpu_fc_names[pcpu_chosen_fc], rc);
>  	}
>  	if (rc < 0)
>  		rc = pcpu_page_first_chunk(PERCPU_FIRST_CHUNK_RESERVE,
> -					   pcpu_fc_alloc, pcpu_fc_free,
>  					   pcpu_cpu_to_node,
>  					   pcpup_populate_pte);
>  	if (rc < 0)
> diff --git a/drivers/base/arch_numa.c b/drivers/base/arch_numa.c
> index 273543d9ff85..23a10cc36165 100644
> --- a/drivers/base/arch_numa.c
> +++ b/drivers/base/arch_numa.c
> @@ -155,20 +155,6 @@ static int __init pcpu_cpu_distance(unsigned int from, unsigned int to)
>  	return node_distance(early_cpu_to_node(from), early_cpu_to_node(to));
>  }
>  
> -static void * __init pcpu_fc_alloc(unsigned int cpu, size_t size, size_t align,
> -				   pcpu_fc_cpu_to_node_fn_t cpu_to_nd_fn)
> -{
> -	int nid = cpu_to_nd_fn(cpu);
> -
> -	return  memblock_alloc_try_nid(size, align,
> -			__pa(MAX_DMA_ADDRESS), MEMBLOCK_ALLOC_ACCESSIBLE, nid);
> -}
> -
> -static void __init pcpu_fc_free(void *ptr, size_t size)
> -{
> -	memblock_free(ptr, size);
> -}
> -
>  #ifdef CONFIG_NEED_PER_CPU_PAGE_FIRST_CHUNK
>  static void __init pcpu_populate_pte(unsigned long addr)
>  {
> @@ -229,8 +215,7 @@ void __init setup_per_cpu_areas(void)
>  		rc = pcpu_embed_first_chunk(PERCPU_MODULE_RESERVE,
>  					    PERCPU_DYNAMIC_RESERVE, PAGE_SIZE,
>  					    pcpu_cpu_distance,
> -					    early_cpu_to_node,
> -					    pcpu_fc_alloc, pcpu_fc_free);
> +					    early_cpu_to_node);
>  #ifdef CONFIG_NEED_PER_CPU_PAGE_FIRST_CHUNK
>  		if (rc < 0)
>  			pr_warn("PERCPU: %s allocator failed (%d), falling back to page size\n",
> @@ -241,8 +226,6 @@ void __init setup_per_cpu_areas(void)
>  #ifdef CONFIG_NEED_PER_CPU_PAGE_FIRST_CHUNK
>  	if (rc < 0)
>  		rc = pcpu_page_first_chunk(PERCPU_MODULE_RESERVE,
> -					   pcpu_fc_alloc,
> -					   pcpu_fc_free,
>  					   early_cpu_to_node,
>  					   pcpu_populate_pte);
>  #endif
> diff --git a/include/linux/percpu.h b/include/linux/percpu.h
> index 41bb54715b0c..d73c97ef4ff4 100644
> --- a/include/linux/percpu.h
> +++ b/include/linux/percpu.h
> @@ -95,9 +95,6 @@ extern const char * const pcpu_fc_names[PCPU_FC_NR];
>  extern enum pcpu_fc pcpu_chosen_fc;
>  
>  typedef int (pcpu_fc_cpu_to_node_fn_t)(int cpu);
> -typedef void * (*pcpu_fc_alloc_fn_t)(unsigned int cpu, size_t size, size_t align,
> -				     pcpu_fc_cpu_to_node_fn_t cpu_to_nd_fn);
> -typedef void (*pcpu_fc_free_fn_t)(void *ptr, size_t size);
>  typedef void (*pcpu_fc_populate_pte_fn_t)(unsigned long addr);
>  typedef int (pcpu_fc_cpu_distance_fn_t)(unsigned int from, unsigned int to);
>  
> @@ -112,15 +109,11 @@ extern void __init pcpu_setup_first_chunk(const struct pcpu_alloc_info *ai,
>  extern int __init pcpu_embed_first_chunk(size_t reserved_size, size_t dyn_size,
>  				size_t atom_size,
>  				pcpu_fc_cpu_distance_fn_t cpu_distance_fn,
> -				pcpu_fc_cpu_to_node_fn_t cpu_to_nd_fn,
> -				pcpu_fc_alloc_fn_t alloc_fn,
> -				pcpu_fc_free_fn_t free_fn);
> +				pcpu_fc_cpu_to_node_fn_t cpu_to_nd_fn);
>  #endif
>  
>  #ifdef CONFIG_NEED_PER_CPU_PAGE_FIRST_CHUNK
>  extern int __init pcpu_page_first_chunk(size_t reserved_size,
> -				pcpu_fc_alloc_fn_t alloc_fn,
> -				pcpu_fc_free_fn_t free_fn,
>  				pcpu_fc_cpu_to_node_fn_t cpu_to_nd_fn,
>  				pcpu_fc_populate_pte_fn_t populate_pte_fn);
>  #endif
> diff --git a/mm/percpu.c b/mm/percpu.c
> index 3f6cf1ff0be2..efaa1cbaf73d 100644
> --- a/mm/percpu.c
> +++ b/mm/percpu.c
> @@ -2992,6 +2992,30 @@ static struct pcpu_alloc_info * __init __flatten pcpu_build_alloc_info(
>  
>  	return ai;
>  }
> +
> +static void * __init pcpu_fc_alloc(unsigned int cpu, size_t size, size_t align,
> +				   pcpu_fc_cpu_to_node_fn_t cpu_to_nd_fn)
> +{
> +	const unsigned long goal = __pa(MAX_DMA_ADDRESS);
> +	int node = NUMA_NO_NODE;
> +	void *ptr;
> +
> +	if (cpu_to_nd_fn)
> +		node = cpu_to_nd_fn(cpu);
> +
> +	if (node == NUMA_NO_NODE || !node_online(node) || !NODE_DATA(node)) {
> +		ptr = memblock_alloc_from(size, align, goal);
> +	} else {
> +		ptr = memblock_alloc_try_nid(size, align, goal,
> +					     MEMBLOCK_ALLOC_ACCESSIBLE, node);
> +	}
> +	return ptr;
> +}

My preference here would be to keep this identical to the x86
implementation where we #ifdef CONFIG_NUMA.

> +
> +static void __init pcpu_fc_free(void *ptr, size_t size)
> +{
> +	memblock_free(ptr, size);
> +}
>  #endif /* BUILD_EMBED_FIRST_CHUNK || BUILD_PAGE_FIRST_CHUNK */
>  
>  #if defined(BUILD_EMBED_FIRST_CHUNK)
> @@ -3002,14 +3026,12 @@ static struct pcpu_alloc_info * __init __flatten pcpu_build_alloc_info(
>   * @atom_size: allocation atom size
>   * @cpu_distance_fn: callback to determine distance between cpus, optional
>   * @cpu_to_nd_fn: callback to convert cpu to it's node, optional
> - * @alloc_fn: function to allocate percpu page
> - * @free_fn: function to free percpu page
>   *
>   * This is a helper to ease setting up embedded first percpu chunk and
>   * can be called where pcpu_setup_first_chunk() is expected.
>   *
>   * If this function is used to setup the first chunk, it is allocated
> - * by calling @alloc_fn and used as-is without being mapped into
> + * by calling pcpu_fc_alloc and used as-is without being mapped into
>   * vmalloc area.  Allocations are always whole multiples of @atom_size
>   * aligned to @atom_size.
>   *
> @@ -3023,7 +3045,7 @@ static struct pcpu_alloc_info * __init __flatten pcpu_build_alloc_info(
>   * @dyn_size specifies the minimum dynamic area size.
>   *
>   * If the needed size is smaller than the minimum or specified unit
> - * size, the leftover is returned using @free_fn.
> + * size, the leftover is returned using pcpu_fc_free.
>   *
>   * RETURNS:
>   * 0 on success, -errno on failure.
> @@ -3031,9 +3053,7 @@ static struct pcpu_alloc_info * __init __flatten pcpu_build_alloc_info(
>  int __init pcpu_embed_first_chunk(size_t reserved_size, size_t dyn_size,
>  				  size_t atom_size,
>  				  pcpu_fc_cpu_distance_fn_t cpu_distance_fn,
> -				  pcpu_fc_cpu_to_node_fn_t cpu_to_nd_fn,
> -				  pcpu_fc_alloc_fn_t alloc_fn,
> -				  pcpu_fc_free_fn_t free_fn)
> +				  pcpu_fc_cpu_to_node_fn_t cpu_to_nd_fn)
>  {
>  	void *base = (void *)ULONG_MAX;
>  	void **areas = NULL;
> @@ -3068,7 +3088,7 @@ int __init pcpu_embed_first_chunk(size_t reserved_size, size_t dyn_size,
>  		BUG_ON(cpu == NR_CPUS);
>  
>  		/* allocate space for the whole group */
> -		ptr = alloc_fn(cpu, gi->nr_units * ai->unit_size, atom_size, cpu_to_nd_fn);
> +		ptr = pcpu_fc_alloc(cpu, gi->nr_units * ai->unit_size, atom_size, cpu_to_nd_fn);
>  		if (!ptr) {
>  			rc = -ENOMEM;
>  			goto out_free_areas;
> @@ -3107,12 +3127,12 @@ int __init pcpu_embed_first_chunk(size_t reserved_size, size_t dyn_size,
>  		for (i = 0; i < gi->nr_units; i++, ptr += ai->unit_size) {
>  			if (gi->cpu_map[i] == NR_CPUS) {
>  				/* unused unit, free whole */
> -				free_fn(ptr, ai->unit_size);
> +				pcpu_fc_free(ptr, ai->unit_size);
>  				continue;
>  			}
>  			/* copy and return the unused part */
>  			memcpy(ptr, __per_cpu_load, ai->static_size);
> -			free_fn(ptr + size_sum, ai->unit_size - size_sum);
> +			pcpu_fc_free(ptr + size_sum, ai->unit_size - size_sum);
>  		}
>  	}
>  
> @@ -3131,7 +3151,7 @@ int __init pcpu_embed_first_chunk(size_t reserved_size, size_t dyn_size,
>  out_free_areas:
>  	for (group = 0; group < ai->nr_groups; group++)
>  		if (areas[group])
> -			free_fn(areas[group],
> +			pcpu_fc_free(areas[group],
>  				ai->groups[group].nr_units * ai->unit_size);
>  out_free:
>  	pcpu_free_alloc_info(ai);
> @@ -3145,8 +3165,6 @@ int __init pcpu_embed_first_chunk(size_t reserved_size, size_t dyn_size,
>  /**
>   * pcpu_page_first_chunk - map the first chunk using PAGE_SIZE pages
>   * @reserved_size: the size of reserved percpu area in bytes
> - * @alloc_fn: function to allocate percpu page, always called with PAGE_SIZE
> - * @free_fn: function to free percpu page, always called with PAGE_SIZE
>   * @cpu_to_nd_fn: callback to convert cpu to it's node, optional
>   * @populate_pte_fn: function to populate pte
>   *
> @@ -3160,8 +3178,6 @@ int __init pcpu_embed_first_chunk(size_t reserved_size, size_t dyn_size,
>   * 0 on success, -errno on failure.
>   */
>  int __init pcpu_page_first_chunk(size_t reserved_size,
> -				 pcpu_fc_alloc_fn_t alloc_fn,
> -				 pcpu_fc_free_fn_t free_fn,
>  				 pcpu_fc_cpu_to_node_fn_t cpu_to_nd_fn,
>  				 pcpu_fc_populate_pte_fn_t populate_pte_fn)
>  {
> @@ -3205,7 +3221,7 @@ int __init pcpu_page_first_chunk(size_t reserved_size,
>  		for (i = 0; i < unit_pages; i++) {
>  			void *ptr;
>  
> -			ptr = alloc_fn(cpu, PAGE_SIZE, PAGE_SIZE, cpu_to_nd_fn);
> +			ptr = pcpu_fc_alloc(cpu, PAGE_SIZE, PAGE_SIZE, cpu_to_nd_fn);
>  			if (!ptr) {
>  				pr_warn("failed to allocate %s page for cpu%u\n",
>  						psize_str, cpu);
> @@ -3257,7 +3273,7 @@ int __init pcpu_page_first_chunk(size_t reserved_size,
>  
>  enomem:
>  	while (--j >= 0)
> -		free_fn(page_address(pages[j]), PAGE_SIZE);
> +		pcpu_fc_free(page_address(pages[j]), PAGE_SIZE);
>  	rc = -ENOMEM;
>  out_free_ar:
>  	memblock_free(pages, pages_size);
> @@ -3282,17 +3298,6 @@ int __init pcpu_page_first_chunk(size_t reserved_size,
>  unsigned long __per_cpu_offset[NR_CPUS] __read_mostly;
>  EXPORT_SYMBOL(__per_cpu_offset);
>  
> -static void * __init pcpu_dfl_fc_alloc(unsigned int cpu, size_t size, size_t align,
> -				       pcpu_fc_cpu_to_node_fn_t cpu_to_nd_fn)
> -{
> -	return  memblock_alloc_from(size, align, __pa(MAX_DMA_ADDRESS));
> -}
> -
> -static void __init pcpu_dfl_fc_free(void *ptr, size_t size)
> -{
> -	memblock_free(ptr, size);
> -}
> -
>  void __init setup_per_cpu_areas(void)
>  {
>  	unsigned long delta;
> @@ -3303,9 +3308,8 @@ void __init setup_per_cpu_areas(void)
>  	 * Always reserve area for module percpu variables.  That's
>  	 * what the legacy allocator did.
>  	 */
> -	rc = pcpu_embed_first_chunk(PERCPU_MODULE_RESERVE,
> -				    PERCPU_DYNAMIC_RESERVE, PAGE_SIZE, NULL, NULL,
> -				    pcpu_dfl_fc_alloc, pcpu_dfl_fc_free);
> +	rc = pcpu_embed_first_chunk(PERCPU_MODULE_RESERVE, PERCPU_DYNAMIC_RESERVE,
> +				    PAGE_SIZE, NULL, NULL);
>  	if (rc < 0)
>  		panic("Failed to initialize percpu areas.");
>  
> -- 
> 2.26.2
> 

Overall this makes sense.

Thanks,
Dennis