Re: [PATCH v10 11/12] mm/vmalloc: Hugepage vmalloc mappings

Nicholas Piggin
2021-01-25T11:38:02Z

Excerpts from Christophe Leroy's message of January 25, 2021 7:14 pm:
>
>
> Le 24/01/2021 à 09:22, Nicholas Piggin a écrit :
>> Support huge page vmalloc mappings. Config option HAVE_ARCH_HUGE_VMALLOC
>> enables support on architectures that define HAVE_ARCH_HUGE_VMAP and
>> supports PMD sized vmap mappings.
>>
>> vmalloc will attempt to allocate PMD-sized pages if allocating PMD size
>> or larger, and fall back to small pages if that was unsuccessful.
>>
>> Architectures must ensure that any arch specific vmalloc allocations
>> that require PAGE_SIZE mappings (e.g., module allocations vs strict
>> module rwx) use the VM_NOHUGE flag to inhibit larger mappings.
>>
>> When hugepage vmalloc mappings are enabled in the next patch, this
>> reduces TLB misses by nearly 30x on a `git diff` workload on a 2-node
>> POWER9 (59,800 -> 2,100) and reduces CPU cycles by 0.54%.
>>
>> This can result in more internal fragmentation and memory overhead for a
>> given allocation, an option nohugevmalloc is added to disable at boot.
>>
>> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
>> ---
>> arch/Kconfig | 10 +++
>> include/linux/vmalloc.h | 18 ++++
>> mm/page_alloc.c | 5 +-
>> mm/vmalloc.c | 192 ++++++++++++++++++++++++++++++----------
>> 4 files changed, 177 insertions(+), 48 deletions(-)
>>
>
>> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
>> index 0377e1d059e5..eef61e0f5170 100644
>> --- a/mm/vmalloc.c
>> +++ b/mm/vmalloc.c
>
>> @@ -2691,15 +2746,18 @@ EXPORT_SYMBOL_GPL(vmap_pfn);
>> #endif /* CONFIG_VMAP_PFN */
>>
>> static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
>> - pgprot_t prot, int node)
>> + pgprot_t prot, unsigned int page_shift,
>> + int node)
>> {
>> const gfp_t nested_gfp = (gfp_mask & GFP_RECLAIM_MASK) | __GFP_ZERO;
>> - unsigned int nr_pages = get_vm_area_size(area) >> PAGE_SHIFT;
>> - unsigned long array_size;
>> - unsigned int i;
>> + unsigned int page_order = page_shift - PAGE_SHIFT;
>> + unsigned long addr = (unsigned long)area->addr;
>> + unsigned long size = get_vm_area_size(area);
>> + unsigned int nr_small_pages = size >> PAGE_SHIFT;
>> struct page **pages;
>> + unsigned int i;
>>
>> - array_size = (unsigned long)nr_pages * sizeof(struct page *);
>> + array_size = (unsigned long)nr_small_pages * sizeof(struct page *);
>
> array_size() is a function in include/linux/overflow.h
>
> For some reason, it breaks the build with your series.

What config? I haven't seen it.

Thanks,
Nick