v4.19.13 snapshot.
diff --git a/mm/page_io.c b/mm/page_io.c
new file mode 100644
index 0000000..aafd19e
--- /dev/null
+++ b/mm/page_io.c
@@ -0,0 +1,434 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * linux/mm/page_io.c
+ *
+ * Copyright (C) 1991, 1992, 1993, 1994 Linus Torvalds
+ *
+ * Swap reorganised 29.12.95,
+ * Asynchronous swapping added 30.12.95. Stephen Tweedie
+ * Removed race in async swapping. 14.4.1996. Bruno Haible
+ * Add swap of shared pages through the page cache. 20.2.1998. Stephen Tweedie
+ * Always use brw_page, life becomes simpler. 12 May 1998 Eric Biederman
+ */
+
+#include <linux/mm.h>
+#include <linux/kernel_stat.h>
+#include <linux/gfp.h>
+#include <linux/pagemap.h>
+#include <linux/swap.h>
+#include <linux/bio.h>
+#include <linux/swapops.h>
+#include <linux/buffer_head.h>
+#include <linux/writeback.h>
+#include <linux/frontswap.h>
+#include <linux/blkdev.h>
+#include <linux/uio.h>
+#include <linux/sched/task.h>
+#include <asm/pgtable.h>
+
+static struct bio *get_swap_bio(gfp_t gfp_flags,
+ struct page *page, bio_end_io_t end_io)
+{
+ int i, nr = hpage_nr_pages(page);
+ struct bio *bio;
+
+ bio = bio_alloc(gfp_flags, nr);
+ if (bio) {
+ struct block_device *bdev;
+
+ bio->bi_iter.bi_sector = map_swap_page(page, &bdev);
+ bio_set_dev(bio, bdev);
+ bio->bi_iter.bi_sector <<= PAGE_SHIFT - 9;
+ bio->bi_end_io = end_io;
+
+ for (i = 0; i < nr; i++)
+ bio_add_page(bio, page + i, PAGE_SIZE, 0);
+ VM_BUG_ON(bio->bi_iter.bi_size != PAGE_SIZE * nr);
+ }
+ return bio;
+}
+
+void end_swap_bio_write(struct bio *bio)
+{
+ struct page *page = bio_first_page_all(bio);
+
+ if (bio->bi_status) {
+ SetPageError(page);
+ /*
+ * We failed to write the page out to swap-space.
+ * Re-dirty the page in order to avoid it being reclaimed.
+ * Also print a dire warning that things will go BAD (tm)
+ * very quickly.
+ *
+ * Also clear PG_reclaim to avoid rotate_reclaimable_page()
+ */
+ set_page_dirty(page);
+ pr_alert("Write-error on swap-device (%u:%u:%llu)\n",
+ MAJOR(bio_dev(bio)), MINOR(bio_dev(bio)),
+ (unsigned long long)bio->bi_iter.bi_sector);
+ ClearPageReclaim(page);
+ }
+ end_page_writeback(page);
+ bio_put(bio);
+}
+
+static void swap_slot_free_notify(struct page *page)
+{
+ struct swap_info_struct *sis;
+ struct gendisk *disk;
+
+ /*
+ * There is no guarantee that the page is in swap cache - the software
+ * suspend code (at least) uses end_swap_bio_read() against a non-
+ * swapcache page. So we must check PG_swapcache before proceeding with
+ * this optimization.
+ */
+ if (unlikely(!PageSwapCache(page)))
+ return;
+
+ sis = page_swap_info(page);
+ if (!(sis->flags & SWP_BLKDEV))
+ return;
+
+ /*
+ * The swap subsystem performs lazy swap slot freeing,
+ * expecting that the page will be swapped out again.
+ * So we can avoid an unnecessary write if the page
+ * isn't redirtied.
+ * This is good for real swap storage because we can
+ * reduce unnecessary I/O and enhance wear-leveling
+ * if an SSD is used as the as swap device.
+ * But if in-memory swap device (eg zram) is used,
+ * this causes a duplicated copy between uncompressed
+ * data in VM-owned memory and compressed data in
+ * zram-owned memory. So let's free zram-owned memory
+ * and make the VM-owned decompressed page *dirty*,
+ * so the page should be swapped out somewhere again if
+ * we again wish to reclaim it.
+ */
+ disk = sis->bdev->bd_disk;
+ if (disk->fops->swap_slot_free_notify) {
+ swp_entry_t entry;
+ unsigned long offset;
+
+ entry.val = page_private(page);
+ offset = swp_offset(entry);
+
+ SetPageDirty(page);
+ disk->fops->swap_slot_free_notify(sis->bdev,
+ offset);
+ }
+}
+
+static void end_swap_bio_read(struct bio *bio)
+{
+ struct page *page = bio_first_page_all(bio);
+ struct task_struct *waiter = bio->bi_private;
+
+ if (bio->bi_status) {
+ SetPageError(page);
+ ClearPageUptodate(page);
+ pr_alert("Read-error on swap-device (%u:%u:%llu)\n",
+ MAJOR(bio_dev(bio)), MINOR(bio_dev(bio)),
+ (unsigned long long)bio->bi_iter.bi_sector);
+ goto out;
+ }
+
+ SetPageUptodate(page);
+ swap_slot_free_notify(page);
+out:
+ unlock_page(page);
+ WRITE_ONCE(bio->bi_private, NULL);
+ bio_put(bio);
+ wake_up_process(waiter);
+ put_task_struct(waiter);
+}
+
+int generic_swapfile_activate(struct swap_info_struct *sis,
+ struct file *swap_file,
+ sector_t *span)
+{
+ struct address_space *mapping = swap_file->f_mapping;
+ struct inode *inode = mapping->host;
+ unsigned blocks_per_page;
+ unsigned long page_no;
+ unsigned blkbits;
+ sector_t probe_block;
+ sector_t last_block;
+ sector_t lowest_block = -1;
+ sector_t highest_block = 0;
+ int nr_extents = 0;
+ int ret;
+
+ blkbits = inode->i_blkbits;
+ blocks_per_page = PAGE_SIZE >> blkbits;
+
+ /*
+ * Map all the blocks into the extent list. This code doesn't try
+ * to be very smart.
+ */
+ probe_block = 0;
+ page_no = 0;
+ last_block = i_size_read(inode) >> blkbits;
+ while ((probe_block + blocks_per_page) <= last_block &&
+ page_no < sis->max) {
+ unsigned block_in_page;
+ sector_t first_block;
+
+ cond_resched();
+
+ first_block = bmap(inode, probe_block);
+ if (first_block == 0)
+ goto bad_bmap;
+
+ /*
+ * It must be PAGE_SIZE aligned on-disk
+ */
+ if (first_block & (blocks_per_page - 1)) {
+ probe_block++;
+ goto reprobe;
+ }
+
+ for (block_in_page = 1; block_in_page < blocks_per_page;
+ block_in_page++) {
+ sector_t block;
+
+ block = bmap(inode, probe_block + block_in_page);
+ if (block == 0)
+ goto bad_bmap;
+ if (block != first_block + block_in_page) {
+ /* Discontiguity */
+ probe_block++;
+ goto reprobe;
+ }
+ }
+
+ first_block >>= (PAGE_SHIFT - blkbits);
+ if (page_no) { /* exclude the header page */
+ if (first_block < lowest_block)
+ lowest_block = first_block;
+ if (first_block > highest_block)
+ highest_block = first_block;
+ }
+
+ /*
+ * We found a PAGE_SIZE-length, PAGE_SIZE-aligned run of blocks
+ */
+ ret = add_swap_extent(sis, page_no, 1, first_block);
+ if (ret < 0)
+ goto out;
+ nr_extents += ret;
+ page_no++;
+ probe_block += blocks_per_page;
+reprobe:
+ continue;
+ }
+ ret = nr_extents;
+ *span = 1 + highest_block - lowest_block;
+ if (page_no == 0)
+ page_no = 1; /* force Empty message */
+ sis->max = page_no;
+ sis->pages = page_no - 1;
+ sis->highest_bit = page_no - 1;
+out:
+ return ret;
+bad_bmap:
+ pr_err("swapon: swapfile has holes\n");
+ ret = -EINVAL;
+ goto out;
+}
+
+/*
+ * We may have stale swap cache pages in memory: notice
+ * them here and get rid of the unnecessary final write.
+ */
+int swap_writepage(struct page *page, struct writeback_control *wbc)
+{
+ int ret = 0;
+
+ if (try_to_free_swap(page)) {
+ unlock_page(page);
+ goto out;
+ }
+ if (frontswap_store(page) == 0) {
+ set_page_writeback(page);
+ unlock_page(page);
+ end_page_writeback(page);
+ goto out;
+ }
+ ret = __swap_writepage(page, wbc, end_swap_bio_write);
+out:
+ return ret;
+}
+
+static sector_t swap_page_sector(struct page *page)
+{
+ return (sector_t)__page_file_index(page) << (PAGE_SHIFT - 9);
+}
+
+static inline void count_swpout_vm_event(struct page *page)
+{
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+ if (unlikely(PageTransHuge(page)))
+ count_vm_event(THP_SWPOUT);
+#endif
+ count_vm_events(PSWPOUT, hpage_nr_pages(page));
+}
+
+int __swap_writepage(struct page *page, struct writeback_control *wbc,
+ bio_end_io_t end_write_func)
+{
+ struct bio *bio;
+ int ret;
+ struct swap_info_struct *sis = page_swap_info(page);
+
+ VM_BUG_ON_PAGE(!PageSwapCache(page), page);
+ if (sis->flags & SWP_FILE) {
+ struct kiocb kiocb;
+ struct file *swap_file = sis->swap_file;
+ struct address_space *mapping = swap_file->f_mapping;
+ struct bio_vec bv = {
+ .bv_page = page,
+ .bv_len = PAGE_SIZE,
+ .bv_offset = 0
+ };
+ struct iov_iter from;
+
+ iov_iter_bvec(&from, ITER_BVEC | WRITE, &bv, 1, PAGE_SIZE);
+ init_sync_kiocb(&kiocb, swap_file);
+ kiocb.ki_pos = page_file_offset(page);
+
+ set_page_writeback(page);
+ unlock_page(page);
+ ret = mapping->a_ops->direct_IO(&kiocb, &from);
+ if (ret == PAGE_SIZE) {
+ count_vm_event(PSWPOUT);
+ ret = 0;
+ } else {
+ /*
+ * In the case of swap-over-nfs, this can be a
+ * temporary failure if the system has limited
+ * memory for allocating transmit buffers.
+ * Mark the page dirty and avoid
+ * rotate_reclaimable_page but rate-limit the
+ * messages but do not flag PageError like
+ * the normal direct-to-bio case as it could
+ * be temporary.
+ */
+ set_page_dirty(page);
+ ClearPageReclaim(page);
+ pr_err_ratelimited("Write error on dio swapfile (%llu)\n",
+ page_file_offset(page));
+ }
+ end_page_writeback(page);
+ return ret;
+ }
+
+ ret = bdev_write_page(sis->bdev, swap_page_sector(page), page, wbc);
+ if (!ret) {
+ count_swpout_vm_event(page);
+ return 0;
+ }
+
+ ret = 0;
+ bio = get_swap_bio(GFP_NOIO, page, end_write_func);
+ if (bio == NULL) {
+ set_page_dirty(page);
+ unlock_page(page);
+ ret = -ENOMEM;
+ goto out;
+ }
+ bio->bi_opf = REQ_OP_WRITE | REQ_SWAP | wbc_to_write_flags(wbc);
+ bio_associate_blkcg_from_page(bio, page);
+ count_swpout_vm_event(page);
+ set_page_writeback(page);
+ unlock_page(page);
+ submit_bio(bio);
+out:
+ return ret;
+}
+
+int swap_readpage(struct page *page, bool synchronous)
+{
+ struct bio *bio;
+ int ret = 0;
+ struct swap_info_struct *sis = page_swap_info(page);
+ blk_qc_t qc;
+ struct gendisk *disk;
+
+ VM_BUG_ON_PAGE(!PageSwapCache(page) && !synchronous, page);
+ VM_BUG_ON_PAGE(!PageLocked(page), page);
+ VM_BUG_ON_PAGE(PageUptodate(page), page);
+ if (frontswap_load(page) == 0) {
+ SetPageUptodate(page);
+ unlock_page(page);
+ goto out;
+ }
+
+ if (sis->flags & SWP_FILE) {
+ struct file *swap_file = sis->swap_file;
+ struct address_space *mapping = swap_file->f_mapping;
+
+ ret = mapping->a_ops->readpage(swap_file, page);
+ if (!ret)
+ count_vm_event(PSWPIN);
+ return ret;
+ }
+
+ ret = bdev_read_page(sis->bdev, swap_page_sector(page), page);
+ if (!ret) {
+ if (trylock_page(page)) {
+ swap_slot_free_notify(page);
+ unlock_page(page);
+ }
+
+ count_vm_event(PSWPIN);
+ return 0;
+ }
+
+ ret = 0;
+ bio = get_swap_bio(GFP_KERNEL, page, end_swap_bio_read);
+ if (bio == NULL) {
+ unlock_page(page);
+ ret = -ENOMEM;
+ goto out;
+ }
+ disk = bio->bi_disk;
+ /*
+ * Keep this task valid during swap readpage because the oom killer may
+ * attempt to access it in the page fault retry time check.
+ */
+ get_task_struct(current);
+ bio->bi_private = current;
+ bio_set_op_attrs(bio, REQ_OP_READ, 0);
+ count_vm_event(PSWPIN);
+ bio_get(bio);
+ qc = submit_bio(bio);
+ while (synchronous) {
+ set_current_state(TASK_UNINTERRUPTIBLE);
+ if (!READ_ONCE(bio->bi_private))
+ break;
+
+ if (!blk_poll(disk->queue, qc))
+ break;
+ }
+ __set_current_state(TASK_RUNNING);
+ bio_put(bio);
+
+out:
+ return ret;
+}
+
+int swap_set_page_dirty(struct page *page)
+{
+ struct swap_info_struct *sis = page_swap_info(page);
+
+ if (sis->flags & SWP_FILE) {
+ struct address_space *mapping = sis->swap_file->f_mapping;
+
+ VM_BUG_ON_PAGE(!PageSwapCache(page), page);
+ return mapping->a_ops->set_page_dirty(page);
+ } else {
+ return __set_page_dirty_no_writeback(page);
+ }
+}