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btrfs: zoned: serialize metadata IO
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We cannot use zone append for writing metadata, because the B-tree nodes
have references to each other using logical address. Without knowing
the address in advance, we cannot construct the tree in the first place.
So we need to serialize write IOs for metadata.

We cannot add a mutex around allocation and submission because metadata
blocks are allocated in an earlier stage to build up B-trees.

Add a zoned_meta_io_lock and hold it during metadata IO submission in
btree_write_cache_pages() to serialize IOs.

Furthermore, this adds a per-block group metadata IO submission pointer
"meta_write_pointer" to ensure sequential writing, which can break when
attempting to write back blocks in an unfinished transaction. If the
writing out failed because of a hole and the write out is for data
integrity (WB_SYNC_ALL), it returns EAGAIN.

A caller like fsync() code should handle this properly e.g. by falling
back to a full transaction commit.

Reviewed-by: Josef Bacik <[email protected]>
Signed-off-by: Naohiro Aota <[email protected]>
Signed-off-by: David Sterba <[email protected]>
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naota authored and kdave committed Feb 9, 2021
1 parent 42c0110 commit 0bc09ca
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Showing 6 changed files with 109 additions and 1 deletion.
1 change: 1 addition & 0 deletions fs/btrfs/block-group.h
Original file line number Diff line number Diff line change
Expand Up @@ -193,6 +193,7 @@ struct btrfs_block_group {
*/
u64 alloc_offset;
u64 zone_unusable;
u64 meta_write_pointer;
};

static inline u64 btrfs_block_group_end(struct btrfs_block_group *block_group)
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1 change: 1 addition & 0 deletions fs/btrfs/ctree.h
Original file line number Diff line number Diff line change
Expand Up @@ -975,6 +975,7 @@ struct btrfs_fs_info {

/* Max size to emit ZONE_APPEND write command */
u64 max_zone_append_size;
struct mutex zoned_meta_io_lock;

#ifdef CONFIG_BTRFS_FS_REF_VERIFY
spinlock_t ref_verify_lock;
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1 change: 1 addition & 0 deletions fs/btrfs/disk-io.c
Original file line number Diff line number Diff line change
Expand Up @@ -2769,6 +2769,7 @@ void btrfs_init_fs_info(struct btrfs_fs_info *fs_info)
mutex_init(&fs_info->delete_unused_bgs_mutex);
mutex_init(&fs_info->reloc_mutex);
mutex_init(&fs_info->delalloc_root_mutex);
mutex_init(&fs_info->zoned_meta_io_lock);
seqlock_init(&fs_info->profiles_lock);

INIT_LIST_HEAD(&fs_info->dirty_cowonly_roots);
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25 changes: 24 additions & 1 deletion fs/btrfs/extent_io.c
Original file line number Diff line number Diff line change
Expand Up @@ -26,6 +26,7 @@
#include "disk-io.h"
#include "subpage.h"
#include "zoned.h"
#include "block-group.h"

static struct kmem_cache *extent_state_cache;
static struct kmem_cache *extent_buffer_cache;
Expand Down Expand Up @@ -4161,6 +4162,7 @@ static int submit_eb_page(struct page *page, struct writeback_control *wbc,
struct extent_buffer **eb_context)
{
struct address_space *mapping = page->mapping;
struct btrfs_block_group *cache = NULL;
struct extent_buffer *eb;
int ret;

Expand Down Expand Up @@ -4193,13 +4195,31 @@ static int submit_eb_page(struct page *page, struct writeback_control *wbc,
if (!ret)
return 0;

if (!btrfs_check_meta_write_pointer(eb->fs_info, eb, &cache)) {
/*
* If for_sync, this hole will be filled with
* trasnsaction commit.
*/
if (wbc->sync_mode == WB_SYNC_ALL && !wbc->for_sync)
ret = -EAGAIN;
else
ret = 0;
free_extent_buffer(eb);
return ret;
}

*eb_context = eb;

ret = lock_extent_buffer_for_io(eb, epd);
if (ret <= 0) {
btrfs_revert_meta_write_pointer(cache, eb);
if (cache)
btrfs_put_block_group(cache);
free_extent_buffer(eb);
return ret;
}
if (cache)
btrfs_put_block_group(cache);
ret = write_one_eb(eb, wbc, epd);
free_extent_buffer(eb);
if (ret < 0)
Expand Down Expand Up @@ -4245,6 +4265,7 @@ int btree_write_cache_pages(struct address_space *mapping,
tag = PAGECACHE_TAG_TOWRITE;
else
tag = PAGECACHE_TAG_DIRTY;
btrfs_zoned_meta_io_lock(fs_info);
retry:
if (wbc->sync_mode == WB_SYNC_ALL)
tag_pages_for_writeback(mapping, index, end);
Expand Down Expand Up @@ -4285,7 +4306,7 @@ int btree_write_cache_pages(struct address_space *mapping,
}
if (ret < 0) {
end_write_bio(&epd, ret);
return ret;
goto out;
}
/*
* If something went wrong, don't allow any metadata write bio to be
Expand Down Expand Up @@ -4320,6 +4341,8 @@ int btree_write_cache_pages(struct address_space *mapping,
ret = -EROFS;
end_write_bio(&epd, ret);
}
out:
btrfs_zoned_meta_io_unlock(fs_info);
return ret;
}

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50 changes: 50 additions & 0 deletions fs/btrfs/zoned.c
Original file line number Diff line number Diff line change
Expand Up @@ -1159,6 +1159,9 @@ int btrfs_load_block_group_zone_info(struct btrfs_block_group *cache, bool new)
ret = -EIO;
}

if (!ret)
cache->meta_write_pointer = cache->alloc_offset + cache->start;

kfree(alloc_offsets);
free_extent_map(em);

Expand Down Expand Up @@ -1317,3 +1320,50 @@ void btrfs_rewrite_logical_zoned(struct btrfs_ordered_extent *ordered)
kfree(logical);
bdput(bdev);
}

bool btrfs_check_meta_write_pointer(struct btrfs_fs_info *fs_info,
struct extent_buffer *eb,
struct btrfs_block_group **cache_ret)
{
struct btrfs_block_group *cache;
bool ret = true;

if (!btrfs_is_zoned(fs_info))
return true;

cache = *cache_ret;

if (cache && (eb->start < cache->start ||
cache->start + cache->length <= eb->start)) {
btrfs_put_block_group(cache);
cache = NULL;
*cache_ret = NULL;
}

if (!cache)
cache = btrfs_lookup_block_group(fs_info, eb->start);

if (cache) {
if (cache->meta_write_pointer != eb->start) {
btrfs_put_block_group(cache);
cache = NULL;
ret = false;
} else {
cache->meta_write_pointer = eb->start + eb->len;
}

*cache_ret = cache;
}

return ret;
}

void btrfs_revert_meta_write_pointer(struct btrfs_block_group *cache,
struct extent_buffer *eb)
{
if (!btrfs_is_zoned(eb->fs_info) || !cache)
return;

ASSERT(cache->meta_write_pointer == eb->start + eb->len);
cache->meta_write_pointer = eb->start;
}
32 changes: 32 additions & 0 deletions fs/btrfs/zoned.h
Original file line number Diff line number Diff line change
Expand Up @@ -50,6 +50,11 @@ bool btrfs_use_zone_append(struct btrfs_inode *inode, struct extent_map *em);
void btrfs_record_physical_zoned(struct inode *inode, u64 file_offset,
struct bio *bio);
void btrfs_rewrite_logical_zoned(struct btrfs_ordered_extent *ordered);
bool btrfs_check_meta_write_pointer(struct btrfs_fs_info *fs_info,
struct extent_buffer *eb,
struct btrfs_block_group **cache_ret);
void btrfs_revert_meta_write_pointer(struct btrfs_block_group *cache,
struct extent_buffer *eb);
#else /* CONFIG_BLK_DEV_ZONED */
static inline int btrfs_get_dev_zone(struct btrfs_device *device, u64 pos,
struct blk_zone *zone)
Expand Down Expand Up @@ -151,6 +156,19 @@ static inline void btrfs_record_physical_zoned(struct inode *inode,
static inline void btrfs_rewrite_logical_zoned(
struct btrfs_ordered_extent *ordered) { }

static inline bool btrfs_check_meta_write_pointer(struct btrfs_fs_info *fs_info,
struct extent_buffer *eb,
struct btrfs_block_group **cache_ret)
{
return true;
}

static inline void btrfs_revert_meta_write_pointer(
struct btrfs_block_group *cache,
struct extent_buffer *eb)
{
}

#endif

static inline bool btrfs_dev_is_sequential(struct btrfs_device *device, u64 pos)
Expand Down Expand Up @@ -242,4 +260,18 @@ static inline bool btrfs_can_zone_reset(struct btrfs_device *device,
return true;
}

static inline void btrfs_zoned_meta_io_lock(struct btrfs_fs_info *fs_info)
{
if (!btrfs_is_zoned(fs_info))
return;
mutex_lock(&fs_info->zoned_meta_io_lock);
}

static inline void btrfs_zoned_meta_io_unlock(struct btrfs_fs_info *fs_info)
{
if (!btrfs_is_zoned(fs_info))
return;
mutex_unlock(&fs_info->zoned_meta_io_lock);
}

#endif

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