Add the ability to insert multiple pages at once to a user VM with
lower PTE spinlock operations.
The intention of this patch-set is to reduce atomic ops for
tcp zerocopy receives, which normally hits the same spinlock multiple
times consecutively.
Signed-off-by: Arjun Roy <arjunroy.kdev@xxxxxxxxx>
Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Signed-off-by: Soheil Hassas Yeganeh <soheil@xxxxxxxxxx>
---
include/linux/mm.h | 2 +
mm/memory.c | 111 ++++++++++++++++++++++++++++++++++++++++++++-
2 files changed, 111 insertions(+), 2 deletions(-)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 29c928ba6b42..a3ac40fbe8fd 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2563,6 +2563,8 @@ struct vm_area_struct *find_extend_vma(struct mm_struct *, unsigned long addr);
int remap_pfn_range(struct vm_area_struct *, unsigned long addr,
unsigned long pfn, unsigned long size, pgprot_t);
int vm_insert_page(struct vm_area_struct *, unsigned long addr, struct page *);
+int vm_insert_pages(struct vm_area_struct *vma, unsigned long addr,
+ struct page **pages, unsigned long *num);
int vm_insert_pfn(struct vm_area_struct *vma, unsigned long addr,
unsigned long pfn);
int vm_insert_pfn_prot(struct vm_area_struct *vma, unsigned long addr,
diff --git a/mm/memory.c b/mm/memory.c
index 7e23a9275386..1655c5feaf32 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1670,8 +1670,7 @@ int zap_vma_ptes(struct vm_area_struct *vma, unsigned long address,
}
EXPORT_SYMBOL_GPL(zap_vma_ptes);
-pte_t *__get_locked_pte(struct mm_struct *mm, unsigned long addr,
- spinlock_t **ptl)
+static pmd_t *walk_to_pmd(struct mm_struct *mm, unsigned long addr)
{
pgd_t *pgd;
p4d_t *p4d;
@@ -1690,6 +1689,16 @@ pte_t *__get_locked_pte(struct mm_struct *mm, unsigned long addr,
return NULL;
VM_BUG_ON(pmd_trans_huge(*pmd));
+ return pmd;
+}
+
+pte_t *__get_locked_pte(struct mm_struct *mm, unsigned long addr,
+ spinlock_t **ptl)
+{
+ pmd_t *pmd = walk_to_pmd(mm, addr);
+
+ if (!pmd)
+ return NULL;
return pte_alloc_map_lock(mm, pmd, addr, ptl);
}
@@ -1714,6 +1723,15 @@ static int insert_page_into_pte_locked(struct mm_struct *mm, pte_t *pte,
return 0;
}
+static int insert_page_in_batch_locked(struct mm_struct *mm, pmd_t *pmd,
+ unsigned long addr, struct page *page, pgprot_t prot)
+{
+ const int err = validate_page_before_insert(page);
+
+ return err ? err : insert_page_into_pte_locked(
+ mm, pte_offset_map(pmd, addr), addr, page, prot);
+}
+
/*
* This is the old fallback for page remapping.
*
@@ -1742,6 +1760,95 @@ static int insert_page(struct vm_area_struct *vma, unsigned long addr,
return retval;
}
+/* insert_pages() amortizes the cost of spinlock operations
+ * when inserting pages in a loop.
+ */
+static int insert_pages(struct vm_area_struct *vma, unsigned long addr,
+ struct page **pages, unsigned long *num, pgprot_t prot)
+{
+ pmd_t *pmd = NULL;
+ spinlock_t *pte_lock = NULL;
+ struct mm_struct *const mm = vma->vm_mm;
+ unsigned long curr_page_idx = 0;
+ unsigned long remaining_pages_total = *num;
+ unsigned long pages_to_write_in_pmd;
+ int ret;
+more:
+ ret = -EFAULT;
+ pmd = walk_to_pmd(mm, addr);
+ if (!pmd)
+ goto out;
+
+ pages_to_write_in_pmd = min_t(unsigned long,
+ remaining_pages_total, PTRS_PER_PTE - pte_index(addr));
+
+ /* Allocate the PTE if necessary; takes PMD lock once only. */
+ ret = -ENOMEM;
+ if (pte_alloc(mm, pmd, addr))
+ goto out;
+ pte_lock = pte_lockptr(mm, pmd);
+
+ while (pages_to_write_in_pmd) {
+ int pte_idx = 0;
+ const int batch_size = min_t(int, pages_to_write_in_pmd, 8);
+
+ spin_lock(pte_lock);
+ for (; pte_idx < batch_size; ++pte_idx) {
+ int err = insert_page_in_batch_locked(mm, pmd,
+ addr, pages[curr_page_idx], prot);
+ if (unlikely(err)) {
+ spin_unlock(pte_lock);
+ ret = err;
+ remaining_pages_total -= pte_idx;
+ goto out;
+ }
+ addr += PAGE_SIZE;
+ ++curr_page_idx;
+ }
+ spin_unlock(pte_lock);
+ pages_to_write_in_pmd -= batch_size;
+ remaining_pages_total -= batch_size;
+ }
+ if (remaining_pages_total)
+ goto more;
+ ret = 0;
+out:
+ *num = remaining_pages_total;
+ return ret;
+}
+
+/**
+ * vm_insert_pages - insert multiple pages into user vma, batching the pmd lock.
+ * @vma: user vma to map to
+ * @addr: target start user address of these pages
+ * @pages: source kernel pages
+ * @num: in: number of pages to map. out: number of pages that were *not*
+ * mapped. (0 means all pages were successfully mapped).
+ *
+ * Preferred over vm_insert_page() when inserting multiple pages.
+ *
+ * In case of error, we may have mapped a subset of the provided
+ * pages. It is the caller's responsibility to account for this case.
+ *
+ * The same restrictions apply as in vm_insert_page().
+ */
+int vm_insert_pages(struct vm_area_struct *vma, unsigned long addr,
+ struct page **pages, unsigned long *num)
+{
+ const unsigned long end_addr = addr + (*num * PAGE_SIZE) - 1;
+
+ if (addr < vma->vm_start || end_addr >= vma->vm_end)
+ return -EFAULT;
+ if (!(vma->vm_flags & VM_MIXEDMAP)) {
+ BUG_ON(down_read_trylock(&vma->vm_mm->mmap_sem));
+ BUG_ON(vma->vm_flags & VM_PFNMAP);
+ vma->vm_flags |= VM_MIXEDMAP;
+ }
+ /* Defer page refcount checking till we're about to map that page. */
+ return insert_pages(vma, addr, pages, num, vma->vm_page_prot);
+}
+EXPORT_SYMBOL(vm_insert_pages);
+
/**
* vm_insert_page - insert single page into user vma
* @vma: user vma to map to
--
2.25.0.rc1.283.g88dfdc4193-goog
