On Thu, Sep 10, 2009 at 09:10:07AM -0400, Theodore Tso wrote: > On Thu, Sep 10, 2009 at 04:34:55PM +0530, Aneesh Kumar K.V wrote: > > mark_buffer_dirty -> __set_page_dirty -> __mark_inode_dirty > > We need to be careful here. First of all, mark_buffer_dirty() on the > code paths you are talking about is being passed a metadata buffer > head. As such, has Jan has pointed out, the bh is part of the buffer > cache, so the page->mapping of associated with bh->b_page is the inode > of the block device --- *not* the ext4 inode. > > Secondly, __set_page_dirty calls __mark_inode_dirty passing in > I_DIRTY_PAGES --- which should be a hint. What Jan is talking about > is where we set the inode flags I_DIRTY_SYNC and I_DIRTY_DATASYNC: > > * I_DIRTY_SYNC Inode is dirty, but doesn't have to be written on > * fdatasync(). i_atime is the usual cause. > * I_DIRTY_DATASYNC Data-related inode changes pending. We keep track of > * these changes separately from I_DIRTY_SYNC so that we > * don't have to write inode on fdatasync() when only > * mtime has changed in it. > > This is important because ext4_sync_file() (which is called by fsync() > and fdatasync()) uses this logic to determine whether or not to call > sync_inode(), which is what will force a commit when wbc.sync_mode is > set to WB_SYNC_ALL. > > In fact, I think the problem is worse than Jan is pointing out, > because it's not enough that vfs_fq_alloc_space() is calling > mark_inode_dirty(), since that only sets I_DIRTY_SYNC. When we touch > i_size or i_block[], we need to make sure that I_DIRTY_DATASYNC is > set, so that fdatasync() will force a commit. > That explained it pretty nicely. Thanks -aneesh -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
