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btrfs: introduce compressed_bio::pending_sectors to trace compressed bio

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For btrfs_submit_compressed_read() and btrfs_submit_compressed_write(),
we have a pretty weird dance around compressed_bio::pending_bios:

  btrfs_submit_compressed_read/write()
  {
	cb = kmalloc()
	refcount_set(&cb->pending_bios, 0);
	bio = btrfs_alloc_bio();

	/* NOTE here, we haven't yet submitted any bio */
	refcount_set(&cb->pending_bios, 1);

	for (pg_index = 0; pg_index < cb->nr_pages; pg_index++) {
		if (submit) {
			/* Here we submit bio, but we always have one
			 * extra pending_bios */
			refcount_inc(&cb->pending_bios);
			ret = btrfs_map_bio();
		}
	}

	/* Submit the last bio */
	ret = btrfs_map_bio();
  }

There are two reasons why we do this:

- compressed_bio::pending_bios is a refcount
  Thus if it's reduced to 0, it can not be increased again.

- To ensure the compressed_bio is not freed by some submitted bios
  If the submitted bio is finished before the next bio submitted,
  we can free the compressed_bio completely.

But the above code is sometimes confusing, and we can do it better by
introducing a new member, compressed_bio::pending_sectors.

Now we use compressed_bio::pending_sectors to indicate whether we have
any pending sectors under IO or not yet submitted.

If pending_sectors == 0, we're definitely the last bio of compressed_bio,
and is OK to release the compressed bio.

Now the workflow looks like this:

  btrfs_submit_compressed_read/write()
  {
	cb = kmalloc()
	atomic_set(&cb->pending_bios, 0);
	refcount_set(&cb->pending_sectors,
		     compressed_len >> sectorsize_bits);
	bio = btrfs_alloc_bio();

	for (pg_index = 0; pg_index < cb->nr_pages; pg_index++) {
		if (submit) {
			refcount_inc(&cb->pending_bios);
			ret = btrfs_map_bio();
		}
	}

	/* Submit the last bio */
	refcount_inc(&cb->pending_bios);
	ret = btrfs_map_bio();
  }

For now we still need pending_bios for later error handling, but will
remove pending_bios eventually after properly handling the errors.

Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Qu Wenruo 2021-09-27 15:21:48 +08:00 committed by David Sterba
parent 6a40491020
commit 6ec9765d74
2 changed files with 47 additions and 35 deletions
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75
fs/btrfs/compression.c
View File

@ -193,6 +193,38 @@ static int check_compressed_csum(struct btrfs_inode *inode, struct bio *bio,
return 0;
}
/*
* Reduce bio and io accounting for a compressed_bio with its corresponding bio.
*
* Return true if there is no pending bio nor io.
* Return false otherwise.
*/
static bool dec_and_test_compressed_bio(struct compressed_bio *cb, struct bio *bio)
{
struct btrfs_fs_info *fs_info = btrfs_sb(cb->inode->i_sb);
unsigned int bi_size = 0;
bool last_io = false;
struct bio_vec *bvec;
struct bvec_iter_all iter_all;
/*
* At endio time, bi_iter.bi_size doesn't represent the real bio size.
* Thus here we have to iterate through all segments to grab correct
* bio size.
*/
bio_for_each_segment_all(bvec, bio, iter_all)
bi_size += bvec->bv_len;
if (bio->bi_status)
cb->errors = 1;
ASSERT(bi_size && bi_size <= cb->compressed_len);
last_io = refcount_sub_and_test(bi_size >> fs_info->sectorsize_bits,
&cb->pending_sectors);
atomic_dec(&cb->pending_bios);
return last_io;
}
/* when we finish reading compressed pages from the disk, we
* decompress them and then run the bio end_io routines on the
* decompressed pages (in the inode address space).
@ -212,13 +244,7 @@ static void end_compressed_bio_read(struct bio *bio)
unsigned int mirror = btrfs_bio(bio)->mirror_num;
int ret = 0;
if (bio->bi_status)
cb->errors = 1;
/* if there are more bios still pending for this compressed
* extent, just exit
*/
if (!refcount_dec_and_test(&cb->pending_bios))
if (!dec_and_test_compressed_bio(cb, bio))
goto out;
/*
@ -336,13 +362,7 @@ static void end_compressed_bio_write(struct bio *bio)
struct page *page;
unsigned int index;
if (bio->bi_status)
cb->errors = 1;
/* if there are more bios still pending for this compressed
* extent, just exit
*/
if (!refcount_dec_and_test(&cb->pending_bios))
if (!dec_and_test_compressed_bio(cb, bio))
goto out;
/* ok, we're the last bio for this extent, step one is to
@ -408,7 +428,8 @@ blk_status_t btrfs_submit_compressed_write(struct btrfs_inode *inode, u64 start,
cb = kmalloc(compressed_bio_size(fs_info, compressed_len), GFP_NOFS);
if (!cb)
return BLK_STS_RESOURCE;
refcount_set(&cb->pending_bios, 0);
atomic_set(&cb->pending_bios, 0);
refcount_set(&cb->pending_sectors, compressed_len >> fs_info->sectorsize_bits);
cb->errors = 0;
cb->inode = &inode->vfs_inode;
cb->start = start;
@ -442,7 +463,6 @@ blk_status_t btrfs_submit_compressed_write(struct btrfs_inode *inode, u64 start,
bio->bi_opf |= REQ_CGROUP_PUNT;
kthread_associate_blkcg(blkcg_css);
}
refcount_set(&cb->pending_bios, 1);
/* create and submit bios for the compressed pages */
bytes_left = compressed_len;
@ -470,13 +490,7 @@ blk_status_t btrfs_submit_compressed_write(struct btrfs_inode *inode, u64 start,
page->mapping = NULL;
if (submit || len < PAGE_SIZE) {
/*
* inc the count before we submit the bio so
* we know the end IO handler won't happen before
* we inc the count. Otherwise, the cb might get
* freed before we're done setting it up
*/
refcount_inc(&cb->pending_bios);
atomic_inc(&cb->pending_bios);
ret = btrfs_bio_wq_end_io(fs_info, bio,
BTRFS_WQ_ENDIO_DATA);
BUG_ON(ret); /* -ENOMEM */
@ -515,6 +529,7 @@ blk_status_t btrfs_submit_compressed_write(struct btrfs_inode *inode, u64 start,
cond_resched();
}
atomic_inc(&cb->pending_bios);
ret = btrfs_bio_wq_end_io(fs_info, bio, BTRFS_WQ_ENDIO_DATA);
BUG_ON(ret); /* -ENOMEM */
@ -734,7 +749,8 @@ blk_status_t btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
if (!cb)
goto out;
refcount_set(&cb->pending_bios, 0);
atomic_set(&cb->pending_bios, 0);
refcount_set(&cb->pending_sectors, compressed_len >> fs_info->sectorsize_bits);
cb->errors = 0;
cb->inode = inode;
cb->mirror_num = mirror_num;
@ -779,7 +795,6 @@ blk_status_t btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
comp_bio->bi_opf = REQ_OP_READ;
comp_bio->bi_private = cb;
comp_bio->bi_end_io = end_compressed_bio_read;
refcount_set(&cb->pending_bios, 1);
for (pg_index = 0; pg_index < nr_pages; pg_index++) {
u32 pg_len = PAGE_SIZE;
@ -808,18 +823,11 @@ blk_status_t btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
if (submit || bio_add_page(comp_bio, page, pg_len, 0) < pg_len) {
unsigned int nr_sectors;
atomic_inc(&cb->pending_bios);
ret = btrfs_bio_wq_end_io(fs_info, comp_bio,
BTRFS_WQ_ENDIO_DATA);
BUG_ON(ret); /* -ENOMEM */
/*
* inc the count before we submit the bio so
* we know the end IO handler won't happen before
* we inc the count. Otherwise, the cb might get
* freed before we're done setting it up
*/
refcount_inc(&cb->pending_bios);
ret = btrfs_lookup_bio_sums(inode, comp_bio, sums);
BUG_ON(ret); /* -ENOMEM */
@ -844,6 +852,7 @@ blk_status_t btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
cur_disk_byte += pg_len;
}
atomic_inc(&cb->pending_bios);
ret = btrfs_bio_wq_end_io(fs_info, comp_bio, BTRFS_WQ_ENDIO_DATA);
BUG_ON(ret); /* -ENOMEM */

7
fs/btrfs/compression.h
View File

@ -28,8 +28,11 @@ struct btrfs_inode;
#define BTRFS_ZLIB_DEFAULT_LEVEL 3
struct compressed_bio {
/* number of bios pending for this compressed extent */
refcount_t pending_bios;
/* Number of bios pending for this compressed extent */
atomic_t pending_bios;
/* Number of sectors with unfinished IO (unsubmitted or unfinished) */
refcount_t pending_sectors;
/* Number of compressed pages in the array */
unsigned int nr_pages;