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author | Jan Kara <jack@suse.cz> | 2014-02-28 09:31:10 +0100 |
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committer | Jan Kara <jack@suse.cz> | 2014-03-04 12:19:26 +0100 |
commit | d680104f3d488ff028f7dd03b0bc055aa5e8ad8d (patch) | |
tree | d6d5c478c383f38240dc7e946a7651d7b2463310 /fs/ext3 | |
parent | 99128addc964d4429d1bb9be5fa9e03ce85b1e68 (diff) | |
download | lwn-d680104f3d488ff028f7dd03b0bc055aa5e8ad8d.tar.gz lwn-d680104f3d488ff028f7dd03b0bc055aa5e8ad8d.zip |
ext3: Update outdated comment before ext3_ordered_writepage()
The comment is heavily outdated. The recursion into the filesystem isn't
possible because we use GFP_NOFS for our allocations, the issue about
block_write_full_page() dirtying tail page is long resolved as well
(that function doesn't dirty buffers at all), and finally we don't start
a transaction if all blocks are already allocated and mapped.
Signed-off-by: Jan Kara <jack@suse.cz>
Diffstat (limited to 'fs/ext3')
-rw-r--r-- | fs/ext3/inode.c | 47 |
1 files changed, 4 insertions, 43 deletions
diff --git a/fs/ext3/inode.c b/fs/ext3/inode.c index 2fef98abb207..4ecf88fb69a8 100644 --- a/fs/ext3/inode.c +++ b/fs/ext3/inode.c @@ -1559,56 +1559,17 @@ static int buffer_unmapped(handle_t *handle, struct buffer_head *bh) } /* - * Note that we always start a transaction even if we're not journalling - * data. This is to preserve ordering: any hole instantiation within - * __block_write_full_page -> ext3_get_block() should be journalled - * along with the data so we don't crash and then get metadata which + * Note that whenever we need to map blocks we start a transaction even if + * we're not journalling data. This is to preserve ordering: any hole + * instantiation within __block_write_full_page -> ext3_get_block() should be + * journalled along with the data so we don't crash and then get metadata which * refers to old data. * * In all journalling modes block_write_full_page() will start the I/O. * - * Problem: - * - * ext3_writepage() -> kmalloc() -> __alloc_pages() -> page_launder() -> - * ext3_writepage() - * - * Similar for: - * - * ext3_file_write() -> generic_file_write() -> __alloc_pages() -> ... - * - * Same applies to ext3_get_block(). We will deadlock on various things like - * lock_journal and i_truncate_mutex. - * - * Setting PF_MEMALLOC here doesn't work - too many internal memory - * allocations fail. - * - * 16May01: If we're reentered then journal_current_handle() will be - * non-zero. We simply *return*. - * - * 1 July 2001: @@@ FIXME: - * In journalled data mode, a data buffer may be metadata against the - * current transaction. But the same file is part of a shared mapping - * and someone does a writepage() on it. - * - * We will move the buffer onto the async_data list, but *after* it has - * been dirtied. So there's a small window where we have dirty data on - * BJ_Metadata. - * - * Note that this only applies to the last partial page in the file. The - * bit which block_write_full_page() uses prepare/commit for. (That's - * broken code anyway: it's wrong for msync()). - * - * It's a rare case: affects the final partial page, for journalled data - * where the file is subject to bith write() and writepage() in the same - * transction. To fix it we'll need a custom block_write_full_page(). - * We'll probably need that anyway for journalling writepage() output. - * * We don't honour synchronous mounts for writepage(). That would be * disastrous. Any write() or metadata operation will sync the fs for * us. - * - * AKPM2: if all the page's buffers are mapped to disk and !data=journal, - * we don't need to open a transaction here. */ static int ext3_ordered_writepage(struct page *page, struct writeback_control *wbc) |