[PATCH 4/4] mm/vmalloc: Hugepage vmalloc mappings
Anshuman Khandual
anshuman.khandual at arm.com
Mon Jun 10 18:53:28 AEST 2019
On 06/10/2019 10:08 AM, Nicholas Piggin wrote:
> For platforms that define HAVE_ARCH_HUGE_VMAP, have vmap allow vmalloc to
> allocate huge pages and map them.
IIUC that extends HAVE_ARCH_HUGE_VMAP from iormap to vmalloc.
>
> This brings dTLB misses for linux kernel tree `git diff` from 45,000 to
> 8,000 on a Kaby Lake KVM guest with 8MB dentry hash and mitigations=off
> (performance is in the noise, under 1% difference, page tables are likely
> to be well cached for this workload). Similar numbers are seen on POWER9.
Sure will try this on arm64.
>
> Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
> ---
> include/asm-generic/4level-fixup.h | 1 +
> include/asm-generic/5level-fixup.h | 1 +
> include/linux/vmalloc.h | 1 +
> mm/vmalloc.c | 132 +++++++++++++++++++++++------
> 4 files changed, 107 insertions(+), 28 deletions(-)
>
> diff --git a/include/asm-generic/4level-fixup.h b/include/asm-generic/4level-fixup.h
> index e3667c9a33a5..3cc65a4dd093 100644
> --- a/include/asm-generic/4level-fixup.h
> +++ b/include/asm-generic/4level-fixup.h
> @@ -20,6 +20,7 @@
> #define pud_none(pud) 0
> #define pud_bad(pud) 0
> #define pud_present(pud) 1
> +#define pud_large(pud) 0
> #define pud_ERROR(pud) do { } while (0)
> #define pud_clear(pud) pgd_clear(pud)
> #define pud_val(pud) pgd_val(pud)
> diff --git a/include/asm-generic/5level-fixup.h b/include/asm-generic/5level-fixup.h
> index bb6cb347018c..c4377db09a4f 100644
> --- a/include/asm-generic/5level-fixup.h
> +++ b/include/asm-generic/5level-fixup.h
> @@ -22,6 +22,7 @@
> #define p4d_none(p4d) 0
> #define p4d_bad(p4d) 0
> #define p4d_present(p4d) 1
> +#define p4d_large(p4d) 0
> #define p4d_ERROR(p4d) do { } while (0)
> #define p4d_clear(p4d) pgd_clear(p4d)
> #define p4d_val(p4d) pgd_val(p4d)
Both of these are required from vmalloc_to_page() which as per a later comment
should be part of a prerequisite patch before this series.
> diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h
> index 812bea5866d6..4c92dc608928 100644
> --- a/include/linux/vmalloc.h
> +++ b/include/linux/vmalloc.h
> @@ -42,6 +42,7 @@ struct vm_struct {
> unsigned long size;
> unsigned long flags;
> struct page **pages;
> + unsigned int page_shift;
So the entire vm_struct will be mapped with a single page_shift. It cannot have
mix and match mappings with PAGE_SIZE, PMD_SIZE, PUD_SIZE etc in case the
allocation fails for larger ones, falling back etc what over other reasons.
> unsigned int nr_pages;
> phys_addr_t phys_addr;
> const void *caller;
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index dd27cfb29b10..0cf8e861caeb 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -36,6 +36,7 @@
> #include <linux/rbtree_augmented.h>
>
> #include <linux/uaccess.h>
> +#include <asm/pgtable.h>
> #include <asm/tlbflush.h>
> #include <asm/shmparam.h>
>
> @@ -440,6 +441,41 @@ static int vmap_pages_range(unsigned long start, unsigned long end,
> return ret;
> }
>
> +#ifdef CONFIG_HAVE_ARCH_HUGE_VMAP
> +static int vmap_hpages_range(unsigned long start, unsigned long end,
A small nit (if you agree) s/hpages/huge_pages/
> + pgprot_t prot, struct page **pages,
Re-order (prot <---> pages) just to follow the standard like before.
> + unsigned int page_shift)
> +{
> + unsigned long addr = start;
> + unsigned int i, nr = (end - start) >> (PAGE_SHIFT + page_shift);
s/nr/nr_huge_pages ?
Also should not we check for the alignment of the range [start...end] with
respect to (1UL << [PAGE_SHIFT + page_shift]).
> +
> + for (i = 0; i < nr; i++) {
> + int err;
> +
> + err = vmap_range_noflush(addr,
> + addr + (PAGE_SIZE << page_shift),
> + __pa(page_address(pages[i])), prot,
> + PAGE_SHIFT + page_shift);
> + if (err)
> + return err;
> +
> + addr += PAGE_SIZE << page_shift;
> + }
> + flush_cache_vmap(start, end);
> +
> + return nr;
> +}
> +#else
> +static int vmap_hpages_range(unsigned long start, unsigned long end,
> + pgprot_t prot, struct page **pages,
> + unsigned int page_shift)
> +{
> + BUG_ON(page_shift != PAGE_SIZE);
> + return vmap_pages_range(start, end, prot, pages);
> +}
> +#endif
> +
> +
> int is_vmalloc_or_module_addr(const void *x)
> {
> /*
> @@ -462,7 +498,7 @@ struct page *vmalloc_to_page(const void *vmalloc_addr)
> {
> unsigned long addr = (unsigned long) vmalloc_addr;
> struct page *page = NULL;
> - pgd_t *pgd = pgd_offset_k(addr);
> + pgd_t *pgd;
> p4d_t *p4d;
> pud_t *pud;
> pmd_t *pmd;
> @@ -474,27 +510,38 @@ struct page *vmalloc_to_page(const void *vmalloc_addr)
> */
> VIRTUAL_BUG_ON(!is_vmalloc_or_module_addr(vmalloc_addr));
>
> + pgd = pgd_offset_k(addr);
> if (pgd_none(*pgd))
> return NULL;
> +
Small nit. Stray line here.
'pgd' related changes here seem to be just cleanups and should not part of this patch.
> p4d = p4d_offset(pgd, addr);
> if (p4d_none(*p4d))
> return NULL;
> - pud = pud_offset(p4d, addr);
> +#ifdef CONFIG_HAVE_ARCH_HUGE_VMAP
> + if (p4d_large(*p4d))
> + return p4d_page(*p4d) + ((addr & ~P4D_MASK) >> PAGE_SHIFT);
> +#endif
> + if (WARN_ON_ONCE(p4d_bad(*p4d)))
> + return NULL;
>
> - /*
> - * Don't dereference bad PUD or PMD (below) entries. This will also
> - * identify huge mappings, which we may encounter on architectures
> - * that define CONFIG_HAVE_ARCH_HUGE_VMAP=y. Such regions will be
> - * identified as vmalloc addresses by is_vmalloc_addr(), but are
> - * not [unambiguously] associated with a struct page, so there is
> - * no correct value to return for them.
> - */
What changed the situation so that we could return struct page for a huge
mapping now ? AFAICT even after this patch, PUD/P4D level huge pages can only
be created with ioremap_page_range() not with vmalloc() which creates PMD
sized mappings only. Hence if it's okay to dereference struct page of a huge
mapping (not withstanding the comment here) it should be part of an earlier
patch fixing it first for existing ioremap_page_range() huge mappings.
> - WARN_ON_ONCE(pud_bad(*pud));
> - if (pud_none(*pud) || pud_bad(*pud))
> + pud = pud_offset(p4d, addr);
> + if (pud_none(*pud))
> + return NULL;
> +#ifdef CONFIG_HAVE_ARCH_HUGE_VMAP
> + if (pud_large(*pud))
> + return pud_page(*pud) + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
> +#endif
> + if (WARN_ON_ONCE(pud_bad(*pud)))
> return NULL;
> +
> pmd = pmd_offset(pud, addr);
> - WARN_ON_ONCE(pmd_bad(*pmd));
> - if (pmd_none(*pmd) || pmd_bad(*pmd))
> + if (pmd_none(*pmd))
> + return NULL;
> +#ifdef CONFIG_HAVE_ARCH_HUGE_VMAP
> + if (pmd_large(*pmd))
> + return pmd_page(*pmd) + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
> +#endif
> + if (WARN_ON_ONCE(pmd_bad(*pmd)))
> return NULL;
At each page table level, we are checking in this order
pXX_none() --> pXX_large() --> pXX_bad()
Are not these alternative orders bit better
pXX_bad() --> pXX_none() --> pXX_large()
Or
pXX_none() --> pXX_bad() --> pXX_large()
Checking for pXX_bad() at the end does not make much sense.
>
> ptep = pte_offset_map(pmd, addr);
> @@ -502,6 +549,7 @@ struct page *vmalloc_to_page(const void *vmalloc_addr)
> if (pte_present(pte))
> page = pte_page(pte);
> pte_unmap(ptep);
> +
Small nit. Stray line here.
> return page;
> }
> EXPORT_SYMBOL(vmalloc_to_page);
> @@ -2185,8 +2233,9 @@ static struct vm_struct *__get_vm_area_node(unsigned long size,
> return NULL;
>
> if (flags & VM_IOREMAP)
> - align = 1ul << clamp_t(int, get_count_order_long(size),
> - PAGE_SHIFT, IOREMAP_MAX_ORDER);
> + align = max(align,
> + 1ul << clamp_t(int, get_count_order_long(size),
> + PAGE_SHIFT, IOREMAP_MAX_ORDER));
>
> area = kzalloc_node(sizeof(*area), gfp_mask & GFP_RECLAIM_MASK, node);
> if (unlikely(!area))
> @@ -2398,7 +2447,7 @@ static void __vunmap(const void *addr, int deallocate_pages)
> struct page *page = area->pages[i];
>
> BUG_ON(!page);
> - __free_pages(page, 0);
> + __free_pages(page, area->page_shift);
area->page_shift' turns out to be effective page order. I think the name here is bit
misleading. s/page_shift/page_order or nr_pages should be better IMHO. page_shift is
not actual shift (1UL << area->shift to get size) nor does it sound like page 'order'.
> }
>
> kvfree(area->pages);
> @@ -2541,14 +2590,17 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
> pgprot_t prot, int node)
> {
> struct page **pages;
> + unsigned long addr = (unsigned long)area->addr;
> + unsigned long size = get_vm_area_size(area);
> + unsigned int page_shift = area->page_shift;
> + unsigned int shift = page_shift + PAGE_SHIFT;
> unsigned int nr_pages, array_size, i;
> const gfp_t nested_gfp = (gfp_mask & GFP_RECLAIM_MASK) | __GFP_ZERO;
> const gfp_t alloc_mask = gfp_mask | __GFP_NOWARN;
> const gfp_t highmem_mask = (gfp_mask & (GFP_DMA | GFP_DMA32)) ?
> - 0 :
> - __GFP_HIGHMEM;
> + 0 : __GFP_HIGHMEM;
>
> - nr_pages = get_vm_area_size(area) >> PAGE_SHIFT;
> + nr_pages = size >> shift;
> array_size = (nr_pages * sizeof(struct page *));
>
> area->nr_pages = nr_pages;
> @@ -2569,10 +2621,8 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
> for (i = 0; i < area->nr_pages; i++) {
> struct page *page;
>
> - if (node == NUMA_NO_NODE)
> - page = alloc_page(alloc_mask|highmem_mask);
> - else
> - page = alloc_pages_node(node, alloc_mask|highmem_mask, 0);
> + page = alloc_pages_node(node,
> + alloc_mask|highmem_mask, page_shift);
alloc_mask remains the exact same like before even for these high order pages.
>
> if (unlikely(!page)) {
> /* Successfully allocated i pages, free them in __vunmap() */
> @@ -2584,8 +2634,9 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
> cond_resched();
> }
>
> - if (map_vm_area(area, prot, pages))
> + if (vmap_hpages_range(addr, addr + size, prot, pages, page_shift) < 0)
> goto fail;
> +
> return area->addr;
>
> fail:
> @@ -2619,22 +2670,39 @@ void *__vmalloc_node_range(unsigned long size, unsigned long align,
> pgprot_t prot, unsigned long vm_flags, int node,
> const void *caller)
> {
> - struct vm_struct *area;
> + struct vm_struct *area = NULL;
> void *addr;
> unsigned long real_size = size;
> + unsigned long real_align = align;
> + unsigned int shift = PAGE_SHIFT;
>
> size = PAGE_ALIGN(size);
> if (!size || (size >> PAGE_SHIFT) > totalram_pages())
> goto fail;
>
> + if (IS_ENABLED(CONFIG_HAVE_ARCH_HUGE_VMAP)) {
> + unsigned long size_per_node;
> +
> + size_per_node = size;
> + if (node == NUMA_NO_NODE)
> + size_per_node /= num_online_nodes();
> + if (size_per_node >= PMD_SIZE)
> + shift = PMD_SHIFT;
There are two problems here.
1. Should not size_per_node be aligned with PMD_SIZE to avoid wasting memory later
because of alignment upwards (making it worse for NUMA_NO_NODE)
2. What about PUD_SIZE which is not considered here at all
3. We should have similar knobs like ioremap controlling different size huge mappings
static int __read_mostly ioremap_p4d_capable;
static int __read_mostly ioremap_pud_capable;
static int __read_mostly ioremap_pmd_capable;
static int __read_mostly ioremap_huge_disabled;
while also giving arch a chance to weigh in through similar overrides like these.
arch_ioremap_[pud|pmd]_supported() ---> probably unifying it for vmalloc()
> + }
> +again:
> + align = max(real_align, 1UL << shift);
> + size = ALIGN(real_size, align);
> +
> area = __get_vm_area_node(size, align, VM_ALLOC | VM_UNINITIALIZED |
> vm_flags, start, end, node, gfp_mask, caller);
> if (!area)
> goto fail;
>
> + area->page_shift = shift - PAGE_SHIFT;
> +
> addr = __vmalloc_area_node(area, gfp_mask, prot, node);
> if (!addr)
> - return NULL;
> + goto fail;
>
> /*
> * In this function, newly allocated vm_struct has VM_UNINITIALIZED
> @@ -2648,8 +2716,16 @@ void *__vmalloc_node_range(unsigned long size, unsigned long align,
> return addr;
>
> fail:
> - warn_alloc(gfp_mask, NULL,
> + if (shift == PMD_SHIFT) {
> + shift = PAGE_SHIFT;
> + goto again;
> + }
PUD_SHIFT should be accommodated here as well while falling back to lower
mapping sizes in case previous allocation attempt fails.
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