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. I think the right thing to do is to create an _ext[34]_mark_inode_dirty() which takes an extra argument, which controls whether or not we set I_DIRTY_SYNC or I_DIRTY_DATASYNC. In fact, most of the time, we want to be setting I_DIRTY_DATASYNC, so we should probably have ext[34]_mark_inode_dirty() call _ext[34]_mark_inode_dirty() with I_DIRTY_DATASYNC, and then create a ext[34]_mark_inode_nodatasync() version passes in I_DIRTY_SYNC. This will cause pdflush to call ext4_write_inode() more frequently, but pdflush calls write_inode with wait=0, and ext4_write_inode() is a no-op in that case. BTW, while I was looking into this, I noted that the comments ahead of ext[34]_mark_inode_dirty are out of date; they date back to a time when when prune_icache actually was responsible for cleaning dirty inodes; these days, that honor is owned by fs-writeback.c and pdflush.) Also, the second half of the comments in ext4_write_inode(), where they reference mark_inode_dirty() are also painfully out of date, and somewhat misleading as a result. Does this make sense to every one? - Ted -- 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
