Commit 8cd3984d authored by Arjun Roy's avatar Arjun Roy Committed by Linus Torvalds
Browse files

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@linux-foundation.org: pte_alloc() no longer takes the `addr' argument]
[arjunroy@google.com: add missing page_count() check to vm_insert_pages()]
  Link: http://lkml.kernel.org/r/20200214005929.104481-1-arjunroy.kdev@gmail.com
[arjunroy@google.com: vm_insert_pages() checks if pte_index defined]
  Link: http://lkml.kernel.org/r/20200228054714.204424-2-arjunroy.kdev@gmail.com


Signed-off-by: default avatarArjun Roy <arjunroy@google.com>
Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarSoheil Hassas Yeganeh <soheil@google.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Cc: David Miller <davem@davemloft.net>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Link: http://lkml.kernel.org/r/20200128025958.43490-2-arjunroy.kdev@gmail.com


Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent c97078bd

include/linux/mm.h

+2 −0
Original line number Diff line number Diff line
@@ -2689,6 +2689,8 @@ 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_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,

mm/memory.c

+127 −2
Original line number Diff line number Diff line
@@ -1419,8 +1419,7 @@ void 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;
@@ -1439,6 +1438,16 @@ 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);

}
@@ -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

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