[PATCH 9/9] ext4: Remove ordered data support from ext4_writepage()

Jan Kara
2022-11-30T16:36:27Z

ext4_writepage() should not be called for ordered data anymore. Remove
support for it from the function.

Signed-off-by: Jan Kara <jack@suse.cz>
---
fs/ext4/inode.c | 116 ++++++------------------------------------------
1 file changed, 13 insertions(+), 103 deletions(-)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index c131b611dabf..0c8e700265f1 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -1642,12 +1642,6 @@ static void ext4_print_free_blocks(struct inode *inode)
return;
}

-static int ext4_bh_delay_or_unwritten(handle_t *handle, struct inode *inode,
- struct buffer_head *bh)
-{
- return (buffer_delay(bh) || buffer_unwritten(bh)) && buffer_dirty(bh);
-}
-
/*
* ext4_insert_delayed_block - adds a delayed block to the extents status
* tree, incrementing the reserved cluster/block
@@ -1962,56 +1956,17 @@ static int __ext4_journalled_writepage(struct page *page,
}

/*
- * Note that we don't need to start a transaction unless we're journaling data
- * because we should have holes filled from ext4_page_mkwrite(). We even don't
- * need to file the inode to the transaction's list in ordered mode because if
- * we are writing back data added by write(), the inode is already there and if
- * we are writing back data modified via mmap(), no one guarantees in which
- * transaction the data will hit the disk. In case we are journaling data, we
- * cannot start transaction directly because transaction start ranks above page
- * lock so we have to do some magic.
- *
- * This function can get called via...
- * - ext4_writepages after taking page lock (have journal handle)
- * - journal_submit_inode_data_buffers (no journal handle)
- * - shrink_page_list via the kswapd/direct reclaim (no journal handle)
- * - grab_page_cache when doing write_begin (have journal handle)
- *
- * We don't do any block allocation in this function. If we have page with
- * multiple blocks we need to write those buffer_heads that are mapped. This
- * is important for mmaped based write. So if we do with blocksize 1K
- * truncate(f, 1024);
- * a = mmap(f, 0, 4096);
- * a[0] = 'a';
- * truncate(f, 4096);
- * we have in the page first buffer_head mapped via page_mkwrite call back
- * but other buffer_heads would be unmapped but dirty (dirty done via the
- * do_wp_page). So writepage should write the first block. If we modify
- * the mmap area beyond 1024 we will again get a page_fault and the
- * page_mkwrite callback will do the block allocation and mark the
- * buffer_heads mapped.
- *
- * We redirty the page if we have any buffer_heads that is either delay or
- * unwritten in the page.
- *
- * We can get recursively called as show below.
- *
- * ext4_writepage() -> kmalloc() -> __alloc_pages() -> page_launder() ->
- * ext4_writepage()
- *
- * But since we don't do any block allocation we should not deadlock.
- * Page also have the dirty flag cleared so we don't get recurive page_lock.
+ * This function is now used only when journaling data. We cannot start
+ * transaction directly because transaction start ranks above page lock so we
+ * have to do some magic.
*/
static int ext4_writepage(struct page *page,
struct writeback_control *wbc)
{
struct folio *folio = page_folio(page);
- int ret = 0;
loff_t size;
unsigned int len;
- struct buffer_head *page_bufs = NULL;
struct inode *inode = page->mapping->host;
- struct ext4_io_submit io_submit;

if (unlikely(ext4_forced_shutdown(EXT4_SB(inode->i_sb)))) {
folio_invalidate(folio, 0, folio_size(folio));
@@ -2036,60 +1991,16 @@ static int ext4_writepage(struct page *page,
return 0;
}

- page_bufs = page_buffers(page);
- /*
- * We cannot do block allocation or other extent handling in this
- * function. If there are buffers needing that, we have to redirty
- * the page. But we may reach here when we do a journal commit via
- * journal_submit_inode_data_buffers() and in that case we must write
- * allocated buffers to achieve data=ordered mode guarantees.
- *
- * Also, if there is only one buffer per page (the fs block
- * size == the page size), if one buffer needs block
- * allocation or needs to modify the extent tree to clear the
- * unwritten flag, we know that the page can't be written at
- * all, so we might as well refuse the write immediately.
- * Unfortunately if the block size != page size, we can't as
- * easily detect this case using ext4_walk_page_buffers(), but
- * for the extremely common case, this is an optimization that
- * skips a useless round trip through ext4_bio_write_page().
- */
- if (ext4_walk_page_buffers(NULL, inode, page_bufs, 0, len, NULL,
- ext4_bh_delay_or_unwritten)) {
- redirty_page_for_writepage(wbc, page);
- if ((current->flags & PF_MEMALLOC) ||
- (inode->i_sb->s_blocksize == PAGE_SIZE)) {
- /*
- * For memory cleaning there's no point in writing only
- * some buffers. So just bail out. Warn if we came here
- * from direct reclaim.
- */
- WARN_ON_ONCE((current->flags & (PF_MEMALLOC|PF_KSWAPD))
- == PF_MEMALLOC);
- unlock_page(page);
- return 0;
- }
- }
-
- if (PageChecked(page) && ext4_should_journal_data(inode))
- /*
- * It's mmapped pagecache. Add buffers and journal it. There
- * doesn't seem much point in redirtying the page here.
- */
- return __ext4_journalled_writepage(page, len);
-
- ext4_io_submit_init(&io_submit, wbc);
- io_submit.io_end = ext4_init_io_end(inode, GFP_NOFS);
- if (!io_submit.io_end) {
- redirty_page_for_writepage(wbc, page);
+ WARN_ON_ONCE(!ext4_should_journal_data(inode));
+ if (!PageChecked(page)) {
unlock_page(page);
- return -ENOMEM;
+ return 0;
}
- ret = ext4_bio_write_page(&io_submit, page, len);
- ext4_io_submit(&io_submit);
- /* Drop io_end reference we got from init */
- ext4_put_io_end_defer(io_submit.io_end);
- return ret;
+ /*
+ * It's mmapped pagecache. Add buffers and journal it. There
+ * doesn't seem much point in redirtying the page here.
+ */
+ return __ext4_journalled_writepage(page, len);
}

static int mpage_submit_page(struct mpage_da_data *mpd, struct page *page)
@@ -3142,9 +3053,8 @@ static int ext4_da_write_end(struct file *file,
* i_disksize since writeback will push i_disksize upto i_size
* eventually. If the end of the current write is > i_size and
* inside an allocated block (ext4_da_should_update_i_disksize()
- * check), we need to update i_disksize here as neither
- * ext4_writepage() nor certain ext4_writepages() paths not
- * allocating blocks update i_disksize.
+ * check), we need to update i_disksize here as ext4_writepages() need
+ * not do it in this case.
*
* Note that we defer inode dirtying to generic_write_end() /
* ext4_da_write_inline_data_end().
--
2.35.3