On 7.09.2018 10:39, Omar Sandoval wrote:
> From: Omar Sandoval <osandov@xxxxxx>
>
> Implement the swap file a_ops on Btrfs. Activation needs to make sure
> that the file can be used as a swap file, which currently means it must
> be fully allocated as nocow with no compression on one device. It must
> also do the proper tracking so that ioctls will not interfere with the
> swap file. Deactivation clears this tracking.
>
> Signed-off-by: Omar Sandoval <osandov@xxxxxx>
> ---
> fs/btrfs/inode.c | 316 +++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 316 insertions(+)
>
> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> index 9357a19d2bff..55aba2d7074c 100644
> --- a/fs/btrfs/inode.c
> +++ b/fs/btrfs/inode.c
> @@ -27,6 +27,7 @@
> #include <linux/uio.h>
> #include <linux/magic.h>
> #include <linux/iversion.h>
> +#include <linux/swap.h>
> #include <asm/unaligned.h>
> #include "ctree.h"
> #include "disk-io.h"
> @@ -10437,6 +10438,319 @@ void btrfs_set_range_writeback(struct extent_io_tree *tree, u64 start, u64 end)
> }
> }
>
> +/*
> + * Add an entry indicating a block group or device which is pinned by a
> + * swapfile. Returns 0 on success, 1 if there is already an entry for it, or a
> + * negative errno on failure.
> + */
> +static int btrfs_add_swapfile_pin(struct inode *inode, void *ptr,
> + bool is_block_group)
> +{
> + struct btrfs_fs_info *fs_info = BTRFS_I(inode)->root->fs_info;
> + struct btrfs_swapfile_pin *sp, *entry;
> + struct rb_node **p;
> + struct rb_node *parent = NULL;
> +
> + sp = kmalloc(sizeof(*sp), GFP_NOFS);
> + if (!sp)
> + return -ENOMEM;
> + sp->ptr = ptr;
> + sp->inode = inode;
> + sp->is_block_group = is_block_group;
> +
> + spin_lock(&fs_info->swapfile_pins_lock);
> + p = &fs_info->swapfile_pins.rb_node;
> + while (*p) {
> + parent = *p;
> + entry = rb_entry(parent, struct btrfs_swapfile_pin, node);
> + if (sp->ptr < entry->ptr ||
> + (sp->ptr == entry->ptr && sp->inode < entry->inode)) {
> + p = &(*p)->rb_left;
> + } else if (sp->ptr > entry->ptr ||
> + (sp->ptr == entry->ptr && sp->inode > entry->inode)) {
> + p = &(*p)->rb_right;
> + } else {
> + spin_unlock(&fs_info->swapfile_pins_lock);
> + kfree(sp);
> + return 1;
> + }
I have to admit this is creative use of pointers but I dislike it:
1. You are not really doing an interval tree of any sorts so rb seems a
bit of an overkill. How many block groups/devices do you expect to have
in the rb tree i.e how many swap files per file system so that the logn
search behavior really matter? Why not a simple linked list and just an
equality comparison of pointers?
2. The code self-admits that using pointers for lt/gr comparison is a
hack since in case pointers match you fall back to checking the inode
pointer
3. There is a discrepancy between the keys used for adding (ptr + inode)
and deletion (just inode)
At the very least this hack needs to be at least mentioned in the
changelog.
> + }
> + rb_link_node(&sp->node, parent, p);
> + rb_insert_color(&sp->node, &fs_info->swapfile_pins);
> + spin_unlock(&fs_info->swapfile_pins_lock);
> + return 0;
> +}
> +
> +static void btrfs_free_swapfile_pins(struct inode *inode)
> +{
> + struct btrfs_fs_info *fs_info = BTRFS_I(inode)->root->fs_info;
> + struct btrfs_swapfile_pin *sp;
> + struct rb_node *node, *next;
> +
> + spin_lock(&fs_info->swapfile_pins_lock);
> + node = rb_first(&fs_info->swapfile_pins);
> + while (node) {
> + next = rb_next(node);
> + sp = rb_entry(node, struct btrfs_swapfile_pin, node);
> + if (sp->inode == inode) {
> + rb_erase(&sp->node, &fs_info->swapfile_pins);
> + if (sp->is_block_group)
> + btrfs_put_block_group(sp->ptr);
> + kfree(sp);
> + }
> + node = next;
> + }
> + spin_unlock(&fs_info->swapfile_pins_lock);
> +}
> +
> +struct btrfs_swap_info {
> + u64 start;
> + u64 block_start;
> + u64 block_len;
> + u64 lowest_ppage;
> + u64 highest_ppage;
> + unsigned long nr_pages;
> + int nr_extents;
> +};
> +
> +static int btrfs_add_swap_extent(struct swap_info_struct *sis,
> + struct btrfs_swap_info *bsi)
> +{
> + unsigned long nr_pages;
> + u64 first_ppage, first_ppage_reported, next_ppage;
what the does extra p stand for - physical?
> + int ret;
> +
> + first_ppage = ALIGN(bsi->block_start, PAGE_SIZE) >> PAGE_SHIFT;
> + next_ppage = ALIGN_DOWN(bsi->block_start + bsi->block_len,
> + PAGE_SIZE) >> PAGE_SHIFT;
> +
> + if (first_ppage >= next_ppage)
> + return 0;
> + nr_pages = next_ppage - first_ppage;
> +
> + first_ppage_reported = first_ppage;
> + if (bsi->start == 0)
> + first_ppage_reported++;
> + if (bsi->lowest_ppage > first_ppage_reported)
> + bsi->lowest_ppage = first_ppage_reported;
> + if (bsi->highest_ppage < (next_ppage - 1))
> + bsi->highest_ppage = next_ppage - 1;
> +
> + ret = add_swap_extent(sis, bsi->nr_pages, nr_pages, first_ppage);
> + if (ret < 0)
> + return ret;
> + bsi->nr_extents += ret;
> + bsi->nr_pages += nr_pages;
> + return 0;
> +}
> +
> +static void btrfs_swap_deactivate(struct file *file)
> +{
> + struct inode *inode = file_inode(file);
> +
> + btrfs_free_swapfile_pins(inode);
> + atomic_dec(&BTRFS_I(inode)->root->nr_swapfiles);
> +}
> +
> +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;
> + struct extent_state *cached_state = NULL;
> + struct extent_map *em = NULL;
> + struct btrfs_device *device = NULL;
> + struct btrfs_swap_info bsi = {
> + .lowest_ppage = (sector_t)-1ULL,
> + };
> + int ret = 0;
> + u64 isize = inode->i_size;
> + u64 start;
> +
> + /*
> + * If the swap file was just created, make sure delalloc is done. If the
> + * file changes again after this, the user is doing something stupid and
> + * we don't really care.
> + */
> + ret = btrfs_wait_ordered_range(inode, 0, (u64)-1);
> + if (ret)
> + return ret;
> +
> + /*
> + * The inode is locked, so these flags won't change after we check them.
> + */
> + if (BTRFS_I(inode)->flags & BTRFS_INODE_COMPRESS) {
> + btrfs_info(fs_info, "swapfile must not be compressed");
> + return -EINVAL;
> + }
> + if (!(BTRFS_I(inode)->flags & BTRFS_INODE_NODATACOW)) {
> + btrfs_info(fs_info, "swapfile must not be copy-on-write");
> + return -EINVAL;
> + }
> +
> + /*
> + * Balance or device remove/replace/resize can move stuff around from
> + * under us. The EXCL_OP flag makes sure they aren't running/won't run
> + * concurrently while we are mapping the swap extents, and
> + * fs_info->swapfile_pins prevents them from running while the swap file
> + * is active and moving the extents. Note that this also prevents a
> + * concurrent device add which isn't actually necessary, but it's not
> + * really worth the trouble to allow it.
> + */
> + if (test_and_set_bit(BTRFS_FS_EXCL_OP, &fs_info->flags))
> + return -EBUSY;
> + /*
> + * Snapshots can create extents which require COW even if NODATACOW is
> + * set. We use this counter to prevent snapshots. We must increment it
> + * before walking the extents because we don't want a concurrent
> + * snapshot to run after we've already checked the extents.
> + */
> + atomic_inc(&BTRFS_I(inode)->root->nr_swapfiles);
> +
> + lock_extent_bits(io_tree, 0, isize - 1, &cached_state);
> + start = 0;
> + while (start < isize) {
> + u64 end, logical_block_start, physical_block_start;
> + struct btrfs_block_group_cache *bg;
> + u64 len = isize - start;
> +
> + em = btrfs_get_extent(BTRFS_I(inode), NULL, 0, start, len, 0);
> + if (IS_ERR(em)) {
> + ret = PTR_ERR(em);
> + goto out;
> + }
> + end = extent_map_end(em);
> +
> + if (em->block_start == EXTENT_MAP_HOLE) {
> + btrfs_info(fs_info, "swapfile must not have 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_info(fs_info, "swapfile must not be inline");
> + ret = -EINVAL;
> + goto out;
> + }
> + if (test_bit(EXTENT_FLAG_COMPRESSED, &em->flags)) {
> + btrfs_info(fs_info, "swapfile must not be compressed");
> + ret = -EINVAL;
> + goto out;
> + }
> +
> + logical_block_start = em->block_start + (start - em->start);
> + len = min(len, em->len - (start - em->start));
> + free_extent_map(em);
> + em = NULL;
> +
> + ret = can_nocow_extent(inode, start, &len, NULL, NULL, NULL);
> + if (ret < 0) {
> + goto out;
> + } else if (ret) {
> + ret = 0;
> + } else {
> + btrfs_info(fs_info, "swapfile must not be copy-on-write");
> + ret = -EINVAL;
> + goto out;
> + }
> +
> + em = btrfs_get_chunk_map(fs_info, logical_block_start, len);
> + if (IS_ERR(em)) {
> + ret = PTR_ERR(em);
> + goto out;
> + }
> +
> + if (em->map_lookup->type & BTRFS_BLOCK_GROUP_PROFILE_MASK) {
> + btrfs_info(fs_info, "swapfile must have single data profile");
> + ret = -EINVAL;
> + goto out;
> + }
> +
> + if (device == NULL) {
> + device = em->map_lookup->stripes[0].dev;
> + ret = btrfs_add_swapfile_pin(inode, device, false);
> + if (ret == 1)
> + ret = 0;
> + else if (ret)
> + goto out;
> + } else if (device != em->map_lookup->stripes[0].dev) {
> + btrfs_info(fs_info, "swapfile must be on one device");
> + ret = -EINVAL;
> + goto out;
> + }
> +
> + physical_block_start = (em->map_lookup->stripes[0].physical +
> + (logical_block_start - em->start));
> + len = min(len, em->len - (logical_block_start - em->start));
> + free_extent_map(em);
> + em = NULL;
> +
> + bg = btrfs_lookup_block_group(fs_info, logical_block_start);
> + if (!bg) {
> + btrfs_info(fs_info, "could not find block group containing swapfile");
> + ret = -EINVAL;
> + goto out;
> + }
> +
> + ret = btrfs_add_swapfile_pin(inode, bg, true);
> + if (ret) {
> + btrfs_put_block_group(bg);
> + if (ret == 1)
> + ret = 0;
> + else
> + goto out;
> + }
> +
> + if (bsi.block_len &&
> + bsi.block_start + bsi.block_len == physical_block_start) {
> + bsi.block_len += len;
> + } else {
> + if (bsi.block_len) {
> + ret = btrfs_add_swap_extent(sis, &bsi);
> + if (ret)
> + goto out;
> + }
> + bsi.start = start;
> + bsi.block_start = physical_block_start;
> + bsi.block_len = len;
> + }
> +
> + start = end;
> + }
> +
> + if (bsi.block_len)
> + ret = btrfs_add_swap_extent(sis, &bsi);
> +
> +out:
> + if (!IS_ERR_OR_NULL(em))
> + free_extent_map(em);
> +
> + unlock_extent_cached(io_tree, 0, isize - 1, &cached_state);
> +
> + if (ret)
> + btrfs_swap_deactivate(file);
> +
> + clear_bit(BTRFS_FS_EXCL_OP, &fs_info->flags);
> +
> + if (ret)
> + return ret;
> +
> + if (device)
> + sis->bdev = device->bdev;
> + *span = bsi.highest_ppage - bsi.lowest_ppage + 1;
> + sis->max = bsi.nr_pages;
> + sis->pages = bsi.nr_pages - 1;
> + sis->highest_bit = bsi.nr_pages - 1;
> + return bsi.nr_extents;
> +}
> +
> static const struct inode_operations btrfs_dir_inode_operations = {
> .getattr = btrfs_getattr,
> .lookup = btrfs_lookup,
> @@ -10514,6 +10828,8 @@ 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 = {
>
