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

Christophe Leroy
2021-01-26T05:25:18Z

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.

> gfp_mask |= __GFP_NOWARN;
> if (!(gfp_mask & (GFP_DMA | GFP_DMA32)))
> gfp_mask |= __GFP_HIGHMEM;