Re: [PATCH v2 2/3] arm64: Support page mapping percpu first chunk allocator

[Kefeng Wang]

On 2021/8/1 23:53, Catalin Marinas wrote:
> On Tue, Jul 20, 2021 at 10:51:04AM +0800, Kefeng Wang wrote:
> > Percpu embedded first chunk allocator is the firstly option, but it
> > could fails on ARM64, eg,
> >    "percpu: max_distance=0x5fcfdc640000 too large for vmalloc space 0x781fefff0000"
> >    "percpu: max_distance=0x600000540000 too large for vmalloc space 0x7dffb7ff0000"
> >    "percpu: max_distance=0x5fff9adb0000 too large for vmalloc space 0x5dffb7ff0000"
> >
> > then we could meet "WARNING: CPU: 15 PID: 461 at vmalloc.c:3087 pcpu_get_vm_areas+0x488/0x838",
> > even the system could not boot successfully.
> >
> > Let's implement page mapping percpu first chunk allocator as a fallback
> > to the embedding allocator to increase the robustness of the system.
> It looks like x86, powerpc and sparc implement their own
> setup_per_cpu_areas(). I had a quick look on finding some commonalities
> but I think it's a lot more hassle to make a generic version out of them
> (powerpc looks the simplest though). I think we could add a generic
> variant with the arm64 support and later migrate other architectures to
> it if possible.
Ok, let's do it later, I could try to make some cleanup after the 
patchset is merged ;)
> The patch looks ok to me otherwise but I'd need an ack from Greg as it
> touches drivers/.

the arch_numa is only used ARM64 and riscv, the 
NEED_PER_CPU_PAGE_FIRST_CHUNK

is not enabled on RISCV, so it's no bad effect.

> BTW, do we need something similar for the non-NUMA
> setup_per_cpu_areas()? I can see this patch only enables
> NEED_PER_CPU_PAGE_FIRST_CHUNK if NUMA.
>
> Leaving the rest of the patch below for Greg.
>
> > Signed-off-by: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
> > ---
> >   arch/arm64/Kconfig       |  4 ++
> >   drivers/base/arch_numa.c | 82 +++++++++++++++++++++++++++++++++++-----
> >   2 files changed, 76 insertions(+), 10 deletions(-)
> >
> > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> > index b5b13a932561..eacb5873ded1 100644
> > --- a/arch/arm64/Kconfig
> > +++ b/arch/arm64/Kconfig
> > @@ -1045,6 +1045,10 @@ config NEED_PER_CPU_EMBED_FIRST_CHUNK
> >   	def_bool y
> >   	depends on NUMA
> >   
> > +config NEED_PER_CPU_PAGE_FIRST_CHUNK
> > +	def_bool y
> > +	depends on NUMA
> > +
> >   source "kernel/Kconfig.hz"
> >   
> >   config ARCH_SPARSEMEM_ENABLE
> > diff --git a/drivers/base/arch_numa.c b/drivers/base/arch_numa.c
> > index 4cc4e117727d..563b2013b75a 100644
> > --- a/drivers/base/arch_numa.c
> > +++ b/drivers/base/arch_numa.c
> > @@ -14,6 +14,7 @@
> >   #include <linux/of.h>
> >   
> >   #include <asm/sections.h>
> > +#include <asm/pgalloc.h>
> >   
> >   struct pglist_data *node_data[MAX_NUMNODES] __read_mostly;
> >   EXPORT_SYMBOL(node_data);
> > @@ -168,22 +169,83 @@ static void __init pcpu_fc_free(void *ptr, size_t size)
> >   	memblock_free_early(__pa(ptr), size);
> >   }
> >   
> > +#ifdef CONFIG_NEED_PER_CPU_PAGE_FIRST_CHUNK
> > +static void __init pcpu_populate_pte(unsigned long addr)
> > +{
> > +	pgd_t *pgd = pgd_offset_k(addr);
> > +	p4d_t *p4d;
> > +	pud_t *pud;
> > +	pmd_t *pmd;
> > +
> > +	p4d = p4d_offset(pgd, addr);
> > +	if (p4d_none(*p4d)) {
> > +		pud_t *new;
> > +
> > +		new = memblock_alloc(PAGE_SIZE, PAGE_SIZE);
> > +		if (!new)
> > +			goto err_alloc;
> > +		p4d_populate(&init_mm, p4d, new);
> > +	}
> > +
> > +	pud = pud_offset(p4d, addr);
> > +	if (pud_none(*pud)) {
> > +		pmd_t *new;
> > +
> > +		new = memblock_alloc(PAGE_SIZE, PAGE_SIZE);
> > +		if (!new)
> > +			goto err_alloc;
> > +		pud_populate(&init_mm, pud, new);
> > +	}
> > +
> > +	pmd = pmd_offset(pud, addr);
> > +	if (!pmd_present(*pmd)) {
> > +		pte_t *new;
> > +
> > +		new = memblock_alloc(PAGE_SIZE, PAGE_SIZE);
> > +		if (!new)
> > +			goto err_alloc;
> > +		pmd_populate_kernel(&init_mm, pmd, new);
> > +	}
> > +
> > +	return;
> > +
> > +err_alloc:
> > +	panic("%s: Failed to allocate %lu bytes align=%lx from=%lx\n",
> > +	      __func__, PAGE_SIZE, PAGE_SIZE, PAGE_SIZE);
> > +}
> > +#endif
> > +
> >   void __init setup_per_cpu_areas(void)
> >   {
> >   	unsigned long delta;
> >   	unsigned int cpu;
> > -	int rc;
> > +	int rc = -EINVAL;
> > +
> > +	if (pcpu_chosen_fc != PCPU_FC_PAGE) {
> > +		/*
> > +		 * 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,
> > +					    pcpu_cpu_distance,
> > +					    pcpu_fc_alloc, pcpu_fc_free);
> > +#ifdef CONFIG_NEED_PER_CPU_PAGE_FIRST_CHUNK
> > +		if (rc < 0)
> > +			pr_warn("PERCPU: %s allocator failed (%d), falling back to page size\n",
> > +				   pcpu_fc_names[pcpu_chosen_fc], rc);
> > +#endif
> > +	}
> >   
> > -	/*
> > -	 * 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,
> > -				    pcpu_cpu_distance,
> > -				    pcpu_fc_alloc, pcpu_fc_free);
> > +#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,
> > +					   pcpu_populate_pte);
> > +#endif
> >   	if (rc < 0)
> > -		panic("Failed to initialize percpu areas.");
> > +		panic("Failed to initialize percpu areas (err=%d).", rc);
> >   
> >   	delta = (unsigned long)pcpu_base_addr - (unsigned long)__per_cpu_start;
> >   	for_each_possible_cpu(cpu)
> > --
> > 2.26.2
> .