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iomap: submit ioends immediately

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Currently the writeback code delays submitting fill ioends until we
reach the end of the folio.  The reason for that is that otherwise
the end I/O handler could clear the writeback bit before we've even
finished submitting all I/O for the folio.

Add a bias to ifs->write_bytes_pending while we are submitting I/O
for a folio so that it never reaches zero until all I/O is completed
to prevent the early writeback bit clearing, and remove the now
superfluous submit_list.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20231207072710.176093-13-hch@lst.de
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>
This commit is contained in:
Christoph Hellwig 2023-12-07 08:27:08 +01:00 committed by Christian Brauner
parent f525152a0f
commit 410bb2ce61
1 changed files with 77 additions and 87 deletions
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164
fs/iomap/buffered-io.c
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@ -1610,30 +1610,34 @@ static void iomap_writepage_end_bio(struct bio *bio)
* Submit the final bio for an ioend.
*
* If @error is non-zero, it means that we have a situation where some part of
* the submission process has failed after we've marked pages for writeback
* and unlocked them. In this situation, we need to fail the bio instead of
* submitting it. This typically only happens on a filesystem shutdown.
* the submission process has failed after we've marked pages for writeback.
* We cannot cancel ioend directly in that case, so call the bio end I/O handler
* with the error status here to run the normal I/O completion handler to clear
* the writeback bit and let the file system proess the errors.
*/
static int
iomap_submit_ioend(struct iomap_writepage_ctx *wpc, struct iomap_ioend *ioend,
int error)
static int iomap_submit_ioend(struct iomap_writepage_ctx *wpc, int error)
{
if (wpc->ops->prepare_ioend)
error = wpc->ops->prepare_ioend(ioend, error);
if (error) {
/*
* If we're failing the IO now, just mark the ioend with an
* error and finish it. This will run IO completion immediately
* as there is only one reference to the ioend at this point in
* time.
*/
ioend->io_bio.bi_status = errno_to_blk_status(error);
bio_endio(&ioend->io_bio);
if (!wpc->ioend)
return error;
/*
* Let the file systems prepare the I/O submission and hook in an I/O
* comletion handler. This also needs to happen in case after a
* failure happened so that the file system end I/O handler gets called
* to clean up.
*/
if (wpc->ops->prepare_ioend)
error = wpc->ops->prepare_ioend(wpc->ioend, error);
if (error) {
wpc->ioend->io_bio.bi_status = errno_to_blk_status(error);
bio_endio(&wpc->ioend->io_bio);
} else {
submit_bio(&wpc->ioend->io_bio);
}
submit_bio(&ioend->io_bio);
return 0;
wpc->ioend = NULL;
return error;
}
static struct iomap_ioend *iomap_alloc_ioend(struct iomap_writepage_ctx *wpc,
@ -1687,19 +1691,28 @@ static bool iomap_can_add_to_ioend(struct iomap_writepage_ctx *wpc, loff_t pos)
/*
* Test to see if we have an existing ioend structure that we could append to
* first; otherwise finish off the current ioend and start another.
*
* If a new ioend is created and cached, the old ioend is submitted to the block
* layer instantly. Batching optimisations are provided by higher level block
* plugging.
*
* At the end of a writeback pass, there will be a cached ioend remaining on the
* writepage context that the caller will need to submit.
*/
static void iomap_add_to_ioend(struct iomap_writepage_ctx *wpc,
static int iomap_add_to_ioend(struct iomap_writepage_ctx *wpc,
struct writeback_control *wbc, struct folio *folio,
struct inode *inode, loff_t pos, struct list_head *iolist)
struct inode *inode, loff_t pos)
{
struct iomap_folio_state *ifs = folio->private;
unsigned len = i_blocksize(inode);
size_t poff = offset_in_folio(folio, pos);
int error;
if (!wpc->ioend || !iomap_can_add_to_ioend(wpc, pos)) {
new_ioend:
if (wpc->ioend)
list_add(&wpc->ioend->io_list, iolist);
error = iomap_submit_ioend(wpc, 0);
if (error)
return error;
wpc->ioend = iomap_alloc_ioend(wpc, wbc, inode, pos);
}
@ -1710,12 +1723,12 @@ new_ioend:
atomic_add(len, &ifs->write_bytes_pending);
wpc->ioend->io_size += len;
wbc_account_cgroup_owner(wbc, &folio->page, len);
return 0;
}
static int iomap_writepage_map_blocks(struct iomap_writepage_ctx *wpc,
struct writeback_control *wbc, struct folio *folio,
struct inode *inode, u64 pos, unsigned *count,
struct list_head *submit_list)
struct inode *inode, u64 pos, unsigned *count)
{
int error;
@ -1732,8 +1745,9 @@ static int iomap_writepage_map_blocks(struct iomap_writepage_ctx *wpc,
case IOMAP_HOLE:
break;
default:
iomap_add_to_ioend(wpc, wbc, folio, inode, pos, submit_list);
(*count)++;
error = iomap_add_to_ioend(wpc, wbc, folio, inode, pos);
if (!error)
(*count)++;
}
fail:
@ -1809,35 +1823,21 @@ static bool iomap_writepage_handle_eof(struct folio *folio, struct inode *inode,
return true;
}
/*
* We implement an immediate ioend submission policy here to avoid needing to
* chain multiple ioends and hence nest mempool allocations which can violate
* the forward progress guarantees we need to provide. The current ioend we're
* adding blocks to is cached in the writepage context, and if the new block
* doesn't append to the cached ioend, it will create a new ioend and cache that
* instead.
*
* If a new ioend is created and cached, the old ioend is returned and queued
* locally for submission once the entire page is processed or an error has been
* detected. While ioends are submitted immediately after they are completed,
* batching optimisations are provided by higher level block plugging.
*
* At the end of a writeback pass, there will be a cached ioend remaining on the
* writepage context that the caller will need to submit.
*/
static int iomap_writepage_map(struct iomap_writepage_ctx *wpc,
struct writeback_control *wbc, struct folio *folio)
{
struct iomap_folio_state *ifs = folio->private;
struct inode *inode = folio->mapping->host;
struct iomap_ioend *ioend, *next;
unsigned len = i_blocksize(inode);
unsigned nblocks = i_blocks_per_folio(inode, folio);
u64 pos = folio_pos(folio);
u64 end_pos = pos + folio_size(folio);
unsigned count = 0;
int error = 0, i;
LIST_HEAD(submit_list);
WARN_ON_ONCE(!folio_test_locked(folio));
WARN_ON_ONCE(folio_test_dirty(folio));
WARN_ON_ONCE(folio_test_writeback(folio));
trace_iomap_writepage(inode, pos, folio_size(folio));
@ -1847,12 +1847,27 @@ static int iomap_writepage_map(struct iomap_writepage_ctx *wpc,
}
WARN_ON_ONCE(end_pos <= pos);
if (!ifs && nblocks > 1) {
ifs = ifs_alloc(inode, folio, 0);
iomap_set_range_dirty(folio, 0, end_pos - pos);
if (nblocks > 1) {
if (!ifs) {
ifs = ifs_alloc(inode, folio, 0);
iomap_set_range_dirty(folio, 0, end_pos - pos);
}
/*
* Keep the I/O completion handler from clearing the writeback
* bit until we have submitted all blocks by adding a bias to
* ifs->write_bytes_pending, which is dropped after submitting
* all blocks.
*/
WARN_ON_ONCE(atomic_read(&ifs->write_bytes_pending) != 0);
atomic_inc(&ifs->write_bytes_pending);
}
WARN_ON_ONCE(ifs && atomic_read(&ifs->write_bytes_pending) != 0);
/*
* Set the writeback bit ASAP, as the I/O completion for the single
* block per folio case happen hit as soon as we're submitting the bio.
*/
folio_start_writeback(folio);
/*
* Walk through the folio to find areas to write back. If we
@ -1863,18 +1878,13 @@ static int iomap_writepage_map(struct iomap_writepage_ctx *wpc,
if (ifs && !ifs_block_is_dirty(folio, ifs, i))
continue;
error = iomap_writepage_map_blocks(wpc, wbc, folio, inode, pos,
&count, &submit_list);
&count);
if (error)
break;
}
if (count)
wpc->nr_folios++;
WARN_ON_ONCE(!wpc->ioend && !list_empty(&submit_list));
WARN_ON_ONCE(!folio_test_locked(folio));
WARN_ON_ONCE(folio_test_writeback(folio));
WARN_ON_ONCE(folio_test_dirty(folio));
/*
* We can have dirty bits set past end of file in page_mkwrite path
* while mapping the last partial folio. Hence it's better to clear
@ -1883,38 +1893,20 @@ static int iomap_writepage_map(struct iomap_writepage_ctx *wpc,
iomap_clear_range_dirty(folio, 0, folio_size(folio));
/*
* If the page hasn't been added to the ioend, it won't be affected by
* I/O completion and we must unlock it now.
* Usually the writeback bit is cleared by the I/O completion handler.
* But we may end up either not actually writing any blocks, or (when
* there are multiple blocks in a folio) all I/O might have finished
* already at this point. In that case we need to clear the writeback
* bit ourselves right after unlocking the page.
*/
if (error && !count) {
folio_unlock(folio);
goto done;
}
folio_start_writeback(folio);
folio_unlock(folio);
/*
* Preserve the original error if there was one; catch
* submission errors here and propagate into subsequent ioend
* submissions.
*/
list_for_each_entry_safe(ioend, next, &submit_list, io_list) {
int error2;
list_del_init(&ioend->io_list);
error2 = iomap_submit_ioend(wpc, ioend, error);
if (error2 && !error)
error = error2;
if (ifs) {
if (atomic_dec_and_test(&ifs->write_bytes_pending))
folio_end_writeback(folio);
} else {
if (!count)
folio_end_writeback(folio);
}
/*
* We can end up here with no error and nothing to write only if we race
* with a partial page truncate on a sub-page block sized filesystem.
*/
if (!count)
folio_end_writeback(folio);
done:
mapping_set_error(inode->i_mapping, error);
return error;
}
@ -1942,9 +1934,7 @@ iomap_writepages(struct address_space *mapping, struct writeback_control *wbc,
wpc->ops = ops;
ret = write_cache_pages(mapping, wbc, iomap_do_writepage, wpc);
if (!wpc->ioend)
return ret;
return iomap_submit_ioend(wpc, wpc->ioend, ret);
return iomap_submit_ioend(wpc, ret);
}
EXPORT_SYMBOL_GPL(iomap_writepages);