From: Arjun Roy <arjunroy@xxxxxxxxxx> Subject: mm/memory.c: add vm_insert_pages() 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. [akpm@xxxxxxxxxxxxxxxxxxxx: pte_alloc() no longer takes the `addr' argument] [arjunroy@xxxxxxxxxx: add missing page_count() check to vm_insert_pages()] Link: http://lkml.kernel.org/r/20200214005929.104481-1-arjunroy.kdev@xxxxxxxxx [arjunroy@xxxxxxxxxx: vm_insert_pages() checks if pte_index defined] Link: http://lkml.kernel.org/r/20200228054714.204424-2-arjunroy.kdev@xxxxxxxxx Link: http://lkml.kernel.org/r/20200128025958.43490-2-arjunroy.kdev@xxxxxxxxx Signed-off-by: Arjun Roy <arjunroy@xxxxxxxxxx> Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx> Signed-off-by: Soheil Hassas Yeganeh <soheil@xxxxxxxxxx> Cc: David Miller <davem@xxxxxxxxxxxxx> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx> Cc: Jason Gunthorpe <jgg@xxxxxxxx> Cc: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- include/linux/mm.h | 2 mm/memory.c | 129 ++++++++++++++++++++++++++++++++++++++++++- 2 files changed, 129 insertions(+), 2 deletions(-) --- a/include/linux/mm.h~mm-add-vm_insert_pages +++ a/include/linux/mm.h @@ -2689,6 +2689,8 @@ struct vm_area_struct *find_extend_vma(s 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_map_pages(struct vm_area_struct *vma, struct page **pages, unsigned long num); int vm_map_pages_zero(struct vm_area_struct *vma, struct page **pages, --- a/mm/memory.c~mm-add-vm_insert_pages +++ a/mm/memory.c @@ -1419,8 +1419,7 @@ void zap_vma_ptes(struct vm_area_struct } 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; @@ -1439,6 +1438,16 @@ pte_t *__get_locked_pte(struct mm_struct 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); } @@ -1491,6 +1500,122 @@ out: return retval; } +#ifdef pte_index +static int insert_page_in_batch_locked(struct mm_struct *mm, pmd_t *pmd, + unsigned long addr, struct page *page, pgprot_t prot) +{ + int err; + + if (!page_count(page)) + return -EINVAL; + err = validate_page_before_insert(page); + return err ? err : insert_page_into_pte_locked( + mm, pte_offset_map(pmd, addr), addr, page, prot); +} + +/* insert_pages() amortizes the cost of spinlock operations + * when inserting pages in a loop. Arch *must* define pte_index. + */ +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)) + 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; +} +#endif /* ifdef pte_index */ + +/** + * 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) +{ +#ifdef pte_index + 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); +#else + unsigned long idx = 0, pgcount = *num; + int err; + + for (; idx < pgcount; ++idx) { + err = vm_insert_page(vma, addr + (PAGE_SIZE * idx), pages[idx]); + if (err) + break; + } + *num = pgcount - idx; + return err; +#endif /* ifdef pte_index */ +} +EXPORT_SYMBOL(vm_insert_pages); + /** * vm_insert_page - insert single page into user vma * @vma: user vma to map to _
