Implement the swap file a_ops on btrfs. Activation does two things:
1. Checks for a usable swap file: it must be fully allocated (no holes),
support direct I/O (so no compressed or inline extents) and must be
eligible for nocow in its entirety in order to avoid doing a bunch of
allocations for a COW when we're already low on memory
2. Pins the extent maps in memory with EXTENT_FLAG_SWAPFILE
Deactivation unpins all of the extent maps.
Signed-off-by: Omar Sandoval <osandov@xxxxxxxxxxx>
---
fs/btrfs/inode.c | 131 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 131 insertions(+)
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 7c2dfb2..76b58d7 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -7191,6 +7191,7 @@ static int btrfs_get_blocks_direct(struct inode *inode, sector_t iblock,
* this will cow the extent, reset the len in case we changed
* it above
*/
+ WARN_ON_ONCE(IS_SWAPFILE(inode));
len = bh_result->b_size;
free_extent_map(em);
em = btrfs_new_extent_direct(inode, start, len);
@@ -9443,6 +9444,134 @@ out_inode:
}
+static void __clear_swapfile_extents(struct inode *inode)
+{
+ u64 isize = inode->i_size;
+ struct extent_map *em;
+ u64 start, len;
+
+ start = 0;
+ while (start < isize) {
+ len = isize - start;
+ em = btrfs_get_extent(inode, NULL, 0, start, len, 0);
+ if (IS_ERR(em))
+ return;
+
+ clear_bit(EXTENT_FLAG_SWAPFILE, &em->flags);
+
+ start = extent_map_end(em);
+ free_extent_map(em);
+ }
+}
+
+static int btrfs_swap_activate(struct swap_info_struct *sis, struct file *file,
+ sector_t *span)
+{
+ struct inode *inode = file_inode(file);
+ struct btrfs_fs_info *fs_info = BTRFS_I(inode)->root->fs_info;
+ struct extent_io_tree *io_tree = &BTRFS_I(inode)->io_tree;
+ int ret = 0;
+ u64 isize = inode->i_size;
+ struct extent_state *cached_state = NULL;
+ struct extent_map *em;
+ u64 start, len;
+
+ if (BTRFS_I(inode)->flags & BTRFS_INODE_COMPRESS) {
+ /* Can't do direct I/O on a compressed file. */
+ btrfs_err(fs_info, "swapfile is compressed");
+ return -EINVAL;
+ }
+ if (!(BTRFS_I(inode)->flags & BTRFS_INODE_NODATACOW)) {
+ /*
+ * Going through the copy-on-write path while swapping pages
+ * in/out and doing a bunch of allocations could stress the
+ * memory management code that got us there in the first place,
+ * and that's sure to be a bad time.
+ */
+ btrfs_err(fs_info, "swapfile is copy-on-write");
+ return -EINVAL;
+ }
+
+ lock_extent_bits(io_tree, 0, isize - 1, 0, &cached_state);
+
+ /*
+ * All of the extents must be allocated and support direct I/O. Inline
+ * extents and compressed extents fall back to buffered I/O, so those
+ * are no good. Additionally, all of the extents must be safe for nocow.
+ */
+ atomic_inc(&BTRFS_I(inode)->root->nr_swapfiles);
+ start = 0;
+ while (start < isize) {
+ len = isize - start;
+ em = btrfs_get_extent(inode, NULL, 0, start, len, 0);
+ if (IS_ERR(em)) {
+ ret = PTR_ERR(em);
+ goto out;
+ }
+
+ if (test_bit(EXTENT_FLAG_VACANCY, &em->flags) ||
+ em->block_start == EXTENT_MAP_HOLE) {
+ btrfs_err(fs_info, "swapfile has holes");
+ ret = -EINVAL;
+ goto out;
+ }
+ if (em->block_start == EXTENT_MAP_INLINE) {
+ /*
+ * It's unlikely we'll ever actually find ourselves
+ * here, as a file small enough to fit inline won't be
+ * big enough to store more than the swap header, but in
+ * case something changes in the future, let's catch it
+ * here rather than later.
+ */
+ btrfs_err(fs_info, "swapfile is inline");
+ ret = -EINVAL;
+ goto out;
+ }
+ if (test_bit(EXTENT_FLAG_COMPRESSED, &em->flags)) {
+ btrfs_err(fs_info, "swapfile is compresed");
+ ret = -EINVAL;
+ goto out;
+ }
+ ret = can_nocow_extent(inode, start, &len, NULL, NULL, NULL);
+ if (ret < 0) {
+ goto out;
+ } else if (ret == 1) {
+ ret = 0;
+ } else {
+ btrfs_err(fs_info, "swapfile has extent requiring COW (%llu-%llu)",
+ start, start + len - 1);
+ ret = -EINVAL;
+ goto out;
+ }
+
+ set_bit(EXTENT_FLAG_SWAPFILE, &em->flags);
+
+ start = extent_map_end(em);
+ free_extent_map(em);
+ }
+
+out:
+ if (ret) {
+ __clear_swapfile_extents(inode);
+ atomic_dec(&BTRFS_I(inode)->root->nr_swapfiles);
+ }
+ unlock_extent_cached(io_tree, 0, isize - 1, &cached_state, GFP_NOFS);
+ return ret;
+}
+
+static void btrfs_swap_deactivate(struct file *file)
+{
+ struct inode *inode = file_inode(file);
+ struct extent_io_tree *io_tree = &BTRFS_I(inode)->io_tree;
+ struct extent_state *cached_state = NULL;
+ u64 isize = inode->i_size;
+
+ lock_extent_bits(io_tree, 0, isize - 1, 0, &cached_state);
+ __clear_swapfile_extents(inode);
+ unlock_extent_cached(io_tree, 0, isize - 1, &cached_state, GFP_NOFS);
+ atomic_dec(&BTRFS_I(inode)->root->nr_swapfiles);
+}
+
static const struct inode_operations btrfs_dir_inode_operations = {
.getattr = btrfs_getattr,
.lookup = btrfs_lookup,
@@ -9520,6 +9649,8 @@ static const struct address_space_operations btrfs_aops = {
.releasepage = btrfs_releasepage,
.set_page_dirty = btrfs_set_page_dirty,
.error_remove_page = generic_error_remove_page,
+ .swap_activate = btrfs_swap_activate,
+ .swap_deactivate = btrfs_swap_deactivate,
};
static const struct address_space_operations btrfs_symlink_aops = {
--
2.1.3
--
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