kernel.git/fs/btrfs/send.c, branch linux-5.19.y

Merge tag 'for-5.19-rc7-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/kdave/linux

2022-07-16T20:48:55Z

Pull btrfs reverts from David Sterba: "Due to a recent report [1] we need to revert the radix tree to xarray conversion patches. There's a problem with sleeping under spinlock, when xa_insert could allocate memory under pressure. We use GFP_NOFS so this is a real problem that we unfortunately did not discover during review. I'm sorry to do such change at rc6 time but the revert is IMO the safer option, there are patches to use mutex instead of the spin locks but that would need more testing. The revert branch has been tested on a few setups, all seem ok. The conversion to xarray will be revisited in the future" Link: https://lore.kernel.org/linux-btrfs/cover.1657097693.git.fdmanana@suse.com/ [1] * tag 'for-5.19-rc7-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/kdave/linux: Revert "btrfs: turn delayed_nodes_tree into an XArray" Revert "btrfs: turn name_cache radix tree into XArray in send_ctx" Revert "btrfs: turn fs_info member buffer_radix into XArray" Revert "btrfs: turn fs_roots_radix in btrfs_fs_info into an XArray"

Revert "btrfs: turn name_cache radix tree into XArray in send_ctx"

2022-07-15T17:14:58Z

This reverts commit 4076942021fe14efecae33bf98566df6dd5ae6f7. Revert the xarray conversion, there's a problem with potential sleep-inside-spinlock [1] when calling xa_insert that triggers GFP_NOFS allocation. The radix tree used the preloading mechanism to avoid sleeping but this is not available in xarray. Conversion from spin lock to mutex is possible but at time of rc6 is riskier than a clean revert. [1] https://lore.kernel.org/linux-btrfs/cover.1657097693.git.fdmanana@suse.com/ Reported-by: Filipe Manana Signed-off-by: David Sterba

Merge tag 'folio-5.19' of git://git.infradead.org/users/willy/pagecache

2022-05-25T02:55:07Z

Pull page cache updates from Matthew Wilcox: - Appoint myself page cache maintainer - Fix how scsicam uses the page cache - Use the memalloc_nofs_save() API to replace AOP_FLAG_NOFS - Remove the AOP flags entirely - Remove pagecache_write_begin() and pagecache_write_end() - Documentation updates - Convert several address_space operations to use folios: - is_dirty_writeback - readpage becomes read_folio - releasepage becomes release_folio - freepage becomes free_folio - Change filler_t to require a struct file pointer be the first argument like ->read_folio * tag 'folio-5.19' of git://git.infradead.org/users/willy/pagecache: (107 commits) nilfs2: Fix some kernel-doc comments Appoint myself page cache maintainer fs: Remove aops->freepage secretmem: Convert to free_folio nfs: Convert to free_folio orangefs: Convert to free_folio fs: Add free_folio address space operation fs: Convert drop_buffers() to use a folio fs: Change try_to_free_buffers() to take a folio jbd2: Convert release_buffer_page() to use a folio jbd2: Convert jbd2_journal_try_to_free_buffers to take a folio reiserfs: Convert release_buffer_page() to use a folio fs: Remove last vestiges of releasepage ubifs: Convert to release_folio reiserfs: Convert to release_folio orangefs: Convert to release_folio ocfs2: Convert to release_folio nilfs2: Remove comment about releasepage nfs: Convert to release_folio jfs: Convert to release_folio ...

btrfs: send: avoid trashing the page cache

2022-05-17T18:14:54Z

A send operation reads extent data using the buffered IO path for getting extent data to send in write commands and this is both because it's simple and to make use of the generic readahead infrastructure, which results in a massive speedup. However this fills the page cache with data that, most of the time, is really only used by the send operation - once the write commands are sent, it's not useful to have the data in the page cache anymore. For large snapshots, bringing all data into the page cache eventually leads to the need to evict other data from the page cache that may be more useful for applications (and kernel subsystems). Even if extents are shared with the subvolume on which a snapshot is based on and the data is currently on the page cache due to being read through the subvolume, attempting to read the data through the snapshot will always result in bringing a new copy of the data into another location in the page cache (there's currently no shared memory for shared extents). So make send evict the data it has read before if when it first opened the inode, its mapping had no pages currently loaded: when inode->i_mapping->nr_pages has a value of 0. Do this instead of deciding based on the return value of filemap_range_has_page() before reading an extent because the generic readahead mechanism may read pages beyond the range we request (and it very often does it), which means a call to filemap_range_has_page() will return true due to the readahead that was triggered when processing a previous extent - we don't have a simple way to distinguish this case from the case where the data was brought into the page cache through someone else. So checking for the mapping number of pages being 0 when we first open the inode is simple, cheap and it generally accomplishes the goal of not trashing the page cache - the only exception is if part of data was previously loaded into the page cache through the snapshot by some other process, in that case we end up not evicting any data send brings into the page cache, just like before this change - but that however is not the common case. Example scenario, on a box with 32G of RAM: $ btrfs subvolume create /mnt/sv1 $ xfs_io -f -c "pwrite 0 4G" /mnt/sv1/file1 $ btrfs subvolume snapshot -r /mnt/sv1 /mnt/snap1 $ free -m total used free shared buff/cache available Mem: 31937 186 26866 0 4883 31297 Swap: 8188 0 8188 # After this we get less 4G of free memory. $ btrfs send /mnt/snap1 >/dev/null $ free -m total used free shared buff/cache available Mem: 31937 186 22814 0 8935 31297 Swap: 8188 0 8188 The same, obviously, applies to an incremental send. Signed-off-by: Filipe Manana Reviewed-by: David Sterba Signed-off-by: David Sterba

btrfs: send: keep the current inode open while processing it

2022-05-16T15:17:33Z

Every time we send a write command, we open the inode, read some data to a buffer and then close the inode. The amount of data we read for each write command is at most 48K, returned by max_send_read_size(), and that corresponds to: BTRFS_SEND_BUF_SIZE - 16K = 48K. In practice this does not add any significant overhead, because the time elapsed between every close (iput()) and open (btrfs_iget()) is very short, so the inode is kept in the VFS's cache after the iput() and it's still there by the time we do the next btrfs_iget(). As between processing extents of the current inode we don't do anything else, it makes sense to keep the inode open after we process its first extent that needs to be sent and keep it open until we start processing the next inode. This serves to facilitate the next change, which aims to avoid having send operations trash the page cache with data extents. Signed-off-by: Filipe Manana Reviewed-by: David Sterba Signed-off-by: David Sterba

btrfs: turn name_cache radix tree into XArray in send_ctx

2022-05-16T15:03:16Z

… and adjust all usages of this object to use the XArray API for the sake of consistency. XArray API provides array semantics, so it is notionally easier to use and understand, and it also takes care of locking for us. None of this makes a real difference in this particular patch, but it does in other places where similar replacements are or have been made and we want to be consistent in our usage of data structures in btrfs. Signed-off-by: Gabriel Niebler Signed-off-by: David Sterba

btrfs: use btrfs_for_each_slot in btrfs_unlink_all_paths

2022-05-16T15:03:08Z

This function can be simplified by refactoring to use the new iterator macro. No functional changes. Signed-off-by: Marcos Paulo de Souza Signed-off-by: Gabriel Niebler Reviewed-by: David Sterba Signed-off-by: David Sterba

btrfs: use btrfs_for_each_slot in process_all_extents

2022-05-16T15:03:08Z

btrfs: use btrfs_for_each_slot in process_all_new_xattrs

2022-05-16T15:03:08Z

btrfs: use btrfs_for_each_slot in process_all_refs

2022-05-16T15:03:08Z