Re: [PATCH 16/19] ext4: Support for synchronous DAX faults
From: Ross Zwisler <hidden>
Date: 2017-10-13 20:58:55
Also in:
linux-fsdevel, linux-xfs
On Wed, Oct 11, 2017 at 10:06:00PM +0200, Jan Kara wrote:
We return IOMAP_F_NEEDDSYNC flag from ext4_iomap_begin() for a synchronous write fault when inode has some uncommitted metadata changes. In the fault handler ext4_dax_fault() we then detect this case, call vfs_fsync_range() to make sure all metadata is committed, and call dax_insert_pfn_mkwrite() to insert page table entry. Note that this will also dirty corresponding radix tree entry which is what we want - fsync(2) will still provide data integrity guarantees for applications not using userspace flushing. And applications using userspace flushing can avoid calling fsync(2) and thus avoid the performance overhead. Signed-off-by: Jan Kara <jack@suse.cz> --- fs/ext4/file.c | 6 +++++- fs/ext4/inode.c | 15 +++++++++++++++ fs/jbd2/journal.c | 17 +++++++++++++++++ include/linux/jbd2.h | 1 + 4 files changed, 38 insertions(+), 1 deletion(-)
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quoted hunk ↗ jump to hunk
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c index 31db875bc7a1..13a198924a0f 100644 --- a/fs/ext4/inode.c +++ b/fs/ext4/inode.c@@ -3394,6 +3394,19 @@ static int ext4_releasepage(struct page *page, gfp_t wait) } #ifdef CONFIG_FS_DAX +static bool ext4_inode_datasync_dirty(struct inode *inode) +{ + journal_t *journal = EXT4_SB(inode->i_sb)->s_journal; + + if (journal) + return !jbd2_transaction_committed(journal, + EXT4_I(inode)->i_datasync_tid); + /* Any metadata buffers to write? */ + if (!list_empty(&inode->i_mapping->private_list)) + return true; + return inode->i_state & I_DIRTY_DATASYNC; +}
I just had 2 quick questions on this: 1) Does ext4 actually use inode->i_mapping->private_list to keep track of dirty metadata buffers? The comment above ext4_write_end() leads me to believe that this list is unused? * ext4 never places buffers on inode->i_mapping->private_list. metadata * buffers are managed internally. Or does the above comment only apply to ext4 with a journal? 2) Where is I_DIRTY_DATASYNC set in inode->i_state? I poked around a bit and couldn't see it. The rest of the patch looks good to me, and you can add: Reviewed-by: Ross Zwisler <redacted>