From ced47a4db4bf823419a68f36943d243fb6ae4bb1 Mon Sep 17 00:00:00 2001 From: Qu Wenruo Date: Thu, 20 Mar 2025 13:53:27 +1030 Subject: [PATCH] btrfs: factor out the main loop of btrfs_buffered_write() into a helper Inside the main loop of btrfs_buffered_write() we are doing a lot of heavy lifting inside a while() loop. This makes it pretty hard to read, factor out the content into a helper, copy_one_range() to do the work. This has no functional change, but with some minor variable renames, e.g. rename all "sector" into "block". Reviewed-by: Johannes Thumshirn Reviewed-by: Filipe Manana Signed-off-by: Qu Wenruo Reviewed-by: David Sterba Signed-off-by: David Sterba --- fs/btrfs/file.c | 286 ++++++++++++++++++++++++------------------------ 1 file changed, 144 insertions(+), 142 deletions(-) diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c index 1234394c7657..023b8abe50a4 100644 --- a/fs/btrfs/file.c +++ b/fs/btrfs/file.c @@ -1149,21 +1149,158 @@ static ssize_t reserve_space(struct btrfs_inode *inode, return reserve_bytes; } +/* + * Do the heavy-lifting work to copy one range into one folio of the page cache. + * + * Return > 0 in case we copied all bytes or just some of them. + * Return 0 if no bytes were copied, in which case the caller should retry. + * Return <0 on error. + */ +static int copy_one_range(struct btrfs_inode *inode, struct iov_iter *iter, + struct extent_changeset **data_reserved, u64 start, + bool nowait) +{ + struct btrfs_fs_info *fs_info = inode->root->fs_info; + struct extent_state *cached_state = NULL; + const size_t block_offset = (start & (fs_info->sectorsize - 1)); + size_t write_bytes = min(iov_iter_count(iter), PAGE_SIZE - offset_in_page(start)); + size_t reserve_bytes; + size_t copied; + size_t dirty_blocks; + size_t num_blocks; + struct folio *folio = NULL; + u64 release_bytes; + int extents_locked; + u64 lockstart; + u64 lockend; + bool only_release_metadata = false; + const unsigned int bdp_flags = (nowait ? BDP_ASYNC : 0); + int ret; + + /* + * Fault all pages before locking them in prepare_one_folio() to avoid + * recursive lock. + */ + if (unlikely(fault_in_iov_iter_readable(iter, write_bytes))) + return -EFAULT; + extent_changeset_release(*data_reserved); + ret = reserve_space(inode, data_reserved, start, &write_bytes, nowait, + &only_release_metadata); + if (ret < 0) + return ret; + reserve_bytes = ret; + release_bytes = reserve_bytes; + +again: + ret = balance_dirty_pages_ratelimited_flags(inode->vfs_inode.i_mapping, + bdp_flags); + if (ret) { + btrfs_delalloc_release_extents(inode, reserve_bytes); + release_space(inode, *data_reserved, start, release_bytes, + only_release_metadata); + return ret; + } + + ret = prepare_one_folio(&inode->vfs_inode, &folio, start, write_bytes, false); + if (ret) { + btrfs_delalloc_release_extents(inode, reserve_bytes); + release_space(inode, *data_reserved, start, release_bytes, + only_release_metadata); + return ret; + } + extents_locked = lock_and_cleanup_extent_if_need(inode, folio, start, + write_bytes, &lockstart, + &lockend, nowait, &cached_state); + if (extents_locked < 0) { + if (!nowait && extents_locked == -EAGAIN) + goto again; + + btrfs_delalloc_release_extents(inode, reserve_bytes); + release_space(inode, *data_reserved, start, release_bytes, + only_release_metadata); + ret = extents_locked; + return ret; + } + + copied = copy_folio_from_iter_atomic(folio, offset_in_folio(folio, start), + write_bytes, iter); + flush_dcache_folio(folio); + + /* + * If we get a partial write, we can end up with partially uptodate + * page. Although if sector size < page size we can handle it, but if + * it's not sector aligned it can cause a lot of complexity, so make + * sure they don't happen by forcing retry this copy. + */ + if (unlikely(copied < write_bytes)) { + if (!folio_test_uptodate(folio)) { + iov_iter_revert(iter, copied); + copied = 0; + } + } + + num_blocks = BTRFS_BYTES_TO_BLKS(fs_info, reserve_bytes); + dirty_blocks = round_up(copied + block_offset, fs_info->sectorsize); + dirty_blocks = BTRFS_BYTES_TO_BLKS(fs_info, dirty_blocks); + + if (copied == 0) + dirty_blocks = 0; + + if (num_blocks > dirty_blocks) { + /* Release everything except the sectors we dirtied. */ + release_bytes -= dirty_blocks << fs_info->sectorsize_bits; + if (only_release_metadata) { + btrfs_delalloc_release_metadata(inode, release_bytes, true); + } else { + const u64 release_start = round_up(start + copied, + fs_info->sectorsize); + + btrfs_delalloc_release_space(inode, *data_reserved, + release_start, release_bytes, + true); + } + } + release_bytes = round_up(copied + block_offset, fs_info->sectorsize); + + ret = btrfs_dirty_folio(inode, folio, start, copied, &cached_state, + only_release_metadata); + /* + * If we have not locked the extent range, because the range's start + * offset is >= i_size, we might still have a non-NULL cached extent + * state, acquired while marking the extent range as delalloc through + * btrfs_dirty_page(). Therefore free any possible cached extent state + * to avoid a memory leak. + */ + if (extents_locked) + unlock_extent(&inode->io_tree, lockstart, lockend, &cached_state); + else + free_extent_state(cached_state); + + btrfs_delalloc_release_extents(inode, reserve_bytes); + if (ret) { + btrfs_drop_folio(fs_info, folio, start, copied); + release_space(inode, *data_reserved, start, release_bytes, + only_release_metadata); + return ret; + } + if (only_release_metadata) + btrfs_check_nocow_unlock(inode); + + btrfs_drop_folio(fs_info, folio, start, copied); + return copied; +} + ssize_t btrfs_buffered_write(struct kiocb *iocb, struct iov_iter *i) { struct file *file = iocb->ki_filp; loff_t pos; struct inode *inode = file_inode(file); - struct btrfs_fs_info *fs_info = inode_to_fs_info(inode); struct extent_changeset *data_reserved = NULL; - u64 lockstart; - u64 lockend; size_t num_written = 0; ssize_t ret; loff_t old_isize; unsigned int ilock_flags = 0; const bool nowait = (iocb->ki_flags & IOCB_NOWAIT); - unsigned int bdp_flags = (nowait ? BDP_ASYNC : 0); if (nowait) ilock_flags |= BTRFS_ILOCK_TRY; @@ -1189,147 +1326,12 @@ ssize_t btrfs_buffered_write(struct kiocb *iocb, struct iov_iter *i) pos = iocb->ki_pos; while (iov_iter_count(i) > 0) { - struct extent_state *cached_state = NULL; - size_t offset = offset_in_page(pos); - size_t sector_offset; - size_t write_bytes = min(iov_iter_count(i), PAGE_SIZE - offset); - size_t reserve_bytes; - size_t copied; - size_t dirty_sectors; - size_t num_sectors; - struct folio *folio = NULL; - u64 release_bytes; - int extents_locked; - bool only_release_metadata = false; - - /* - * Fault pages before locking them in prepare_one_folio() - * to avoid recursive lock - */ - if (unlikely(fault_in_iov_iter_readable(i, write_bytes))) { - ret = -EFAULT; - break; - } - - sector_offset = pos & (fs_info->sectorsize - 1); - - extent_changeset_release(data_reserved); - ret = reserve_space(BTRFS_I(inode), &data_reserved, pos, - &write_bytes, nowait, &only_release_metadata); + ret = copy_one_range(BTRFS_I(inode), i, &data_reserved, pos, nowait); if (ret < 0) break; - reserve_bytes = ret; - release_bytes = reserve_bytes; -again: - ret = balance_dirty_pages_ratelimited_flags(inode->i_mapping, bdp_flags); - if (ret) { - btrfs_delalloc_release_extents(BTRFS_I(inode), reserve_bytes); - release_space(BTRFS_I(inode), data_reserved, - pos, release_bytes, only_release_metadata); - break; - } - - ret = prepare_one_folio(inode, &folio, pos, write_bytes, false); - if (ret) { - btrfs_delalloc_release_extents(BTRFS_I(inode), - reserve_bytes); - release_space(BTRFS_I(inode), data_reserved, - pos, release_bytes, only_release_metadata); - break; - } - - extents_locked = lock_and_cleanup_extent_if_need(BTRFS_I(inode), - folio, pos, write_bytes, &lockstart, - &lockend, nowait, &cached_state); - if (extents_locked < 0) { - if (!nowait && extents_locked == -EAGAIN) - goto again; - - btrfs_delalloc_release_extents(BTRFS_I(inode), - reserve_bytes); - release_space(BTRFS_I(inode), data_reserved, - pos, release_bytes, only_release_metadata); - ret = extents_locked; - break; - } - - copied = copy_folio_from_iter_atomic(folio, - offset_in_folio(folio, pos), write_bytes, i); - flush_dcache_folio(folio); - - /* - * If we get a partial write, we can end up with partially - * uptodate page. Although if sector size < page size we can - * handle it, but if it's not sector aligned it can cause - * a lot of complexity, so make sure they don't happen by - * forcing retry this copy. - */ - if (unlikely(copied < write_bytes)) { - if (!folio_test_uptodate(folio)) { - iov_iter_revert(i, copied); - copied = 0; - } - } - - num_sectors = BTRFS_BYTES_TO_BLKS(fs_info, reserve_bytes); - dirty_sectors = round_up(copied + sector_offset, - fs_info->sectorsize); - dirty_sectors = BTRFS_BYTES_TO_BLKS(fs_info, dirty_sectors); - - if (copied == 0) - dirty_sectors = 0; - - if (num_sectors > dirty_sectors) { - /* release everything except the sectors we dirtied */ - release_bytes -= dirty_sectors << fs_info->sectorsize_bits; - if (only_release_metadata) { - btrfs_delalloc_release_metadata(BTRFS_I(inode), - release_bytes, true); - } else { - u64 release_start = round_up(pos + copied, - fs_info->sectorsize); - btrfs_delalloc_release_space(BTRFS_I(inode), - data_reserved, release_start, - release_bytes, true); - } - } - - release_bytes = round_up(copied + sector_offset, - fs_info->sectorsize); - - ret = btrfs_dirty_folio(BTRFS_I(inode), folio, pos, copied, - &cached_state, only_release_metadata); - - /* - * If we have not locked the extent range, because the range's - * start offset is >= i_size, we might still have a non-NULL - * cached extent state, acquired while marking the extent range - * as delalloc through btrfs_dirty_page(). Therefore free any - * possible cached extent state to avoid a memory leak. - */ - if (extents_locked) - unlock_extent(&BTRFS_I(inode)->io_tree, lockstart, - lockend, &cached_state); - else - free_extent_state(cached_state); - - btrfs_delalloc_release_extents(BTRFS_I(inode), reserve_bytes); - if (ret) { - btrfs_drop_folio(fs_info, folio, pos, copied); - release_space(BTRFS_I(inode), data_reserved, - pos, release_bytes, only_release_metadata); - break; - } - - if (only_release_metadata) - btrfs_check_nocow_unlock(BTRFS_I(inode)); - - btrfs_drop_folio(fs_info, folio, pos, copied); - + pos += ret; + num_written += ret; cond_resched(); - - pos += copied; - num_written += copied; } extent_changeset_free(data_reserved); -- 2.50.1