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bcachefs: Add block plugging to read paths

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This will help with some of the btree_trans srcu lock hold time warnings
that are still turning up; submit_bio() can block for awhile if the
device is sufficiently congested.

It's not a perfect solution since blk_plug bios are submitted when
scheduling; we might want a way to disable the "submit on context
switch" behaviour, or switch to our own plugging in the future.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
This commit is contained in:
Kent Overstreet 2024-10-14 21:35:44 -04:00
parent c4bfe7049c
commit b6a562e6d8
2 changed files with 23 additions and 1 deletions
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19
fs/bcachefs/fs-io-buffered.c
View File

@ -248,6 +248,7 @@ void bch2_readahead(struct readahead_control *ractl)
struct bch_io_opts opts;
struct folio *folio;
struct readpages_iter readpages_iter;
struct blk_plug plug;
bch2_inode_opts_get(&opts, c, &inode->ei_inode);
@ -255,6 +256,16 @@ void bch2_readahead(struct readahead_control *ractl)
if (ret)
return;
/*
* Besides being a general performance optimization, plugging helps with
* avoiding btree transaction srcu warnings - submitting a bio can
* block, and we don't want todo that with the transaction locked.
*
* However, plugged bios are submitted when we schedule; we ideally
* would have our own scheduler hook to call unlock_long() before
* scheduling.
*/
blk_start_plug(&plug);
bch2_pagecache_add_get(inode);
struct btree_trans *trans = bch2_trans_get(c);
@ -281,7 +292,7 @@ void bch2_readahead(struct readahead_control *ractl)
bch2_trans_put(trans);
bch2_pagecache_add_put(inode);
blk_finish_plug(&plug);
darray_exit(&readpages_iter.folios);
}
@ -296,9 +307,13 @@ int bch2_read_single_folio(struct folio *folio, struct address_space *mapping)
struct bch_fs *c = inode->v.i_sb->s_fs_info;
struct bch_read_bio *rbio;
struct bch_io_opts opts;
struct blk_plug plug;
int ret;
DECLARE_COMPLETION_ONSTACK(done);
BUG_ON(folio_test_uptodate(folio));
BUG_ON(folio_test_dirty(folio));
if (!bch2_folio_create(folio, GFP_KERNEL))
return -ENOMEM;
@ -313,7 +328,9 @@ int bch2_read_single_folio(struct folio *folio, struct address_space *mapping)
rbio->bio.bi_iter.bi_sector = folio_sector(folio);
BUG_ON(!bio_add_folio(&rbio->bio, folio, folio_size(folio), 0));
blk_start_plug(&plug);
bch2_trans_run(c, (bchfs_read(trans, rbio, inode_inum(inode), NULL), 0));
blk_finish_plug(&plug);
wait_for_completion(&done);
ret = blk_status_to_errno(rbio->bio.bi_status);

5
fs/bcachefs/fs-io-direct.c
View File

@ -70,6 +70,7 @@ static int bch2_direct_IO_read(struct kiocb *req, struct iov_iter *iter)
struct bch_io_opts opts;
struct dio_read *dio;
struct bio *bio;
struct blk_plug plug;
loff_t offset = req->ki_pos;
bool sync = is_sync_kiocb(req);
size_t shorten;
@ -128,6 +129,8 @@ static int bch2_direct_IO_read(struct kiocb *req, struct iov_iter *iter)
*/
dio->should_dirty = iter_is_iovec(iter);
blk_start_plug(&plug);
goto start;
while (iter->count) {
bio = bio_alloc_bioset(NULL,
@ -160,6 +163,8 @@ static int bch2_direct_IO_read(struct kiocb *req, struct iov_iter *iter)
bch2_read(c, rbio_init(bio, opts), inode_inum(inode));
}
blk_finish_plug(&plug);
iter->count += shorten;
if (sync) {