• Wu Fengguang's avatar
    writeback: merge for_kupdate and !for_kupdate cases · a50aeb40
    Wu Fengguang authored
    Unify the logic for kupdate and non-kupdate cases.  There won't be
    starvation because the inodes requeued into b_more_io will later be
    spliced _after_ the remaining inodes in b_io, hence won't stand in the way
    of other inodes in the next run.
    
    It avoids unnecessary redirty_tail() calls, hence the update of
    i_dirtied_when.  The timestamp update is undesirable because it could
    later delay the inode's periodic writeback, or may exclude the inode from
    the data integrity sync operation (which checks timestamp to avoid extra
    work and livelock).
    
    ===
    How the redirty_tail() comes about:
    
    It was a long story..  This redirty_tail() was introduced with
    wbc.more_io.  The initial patch for more_io actually does not have the
    redirty_tail(), and when it's merged, several 100% iowait bug reports
    arised:
    
    reiserfs:
            http://lkml.org/lkml/2007/10/23/93
    
    jfs:
            commit 29a424f2
            JFS: clear PAGECACHE_TAG_DIRTY for no-write pages
    
    ext2:
            http://www.spinics.net/linux/lists/linux-ext4/msg04762.html
    
    They are all old bugs hidden in various filesystems that become "visible"
    with the more_io patch.  At the time, the ext2 bug is thought to be
    "trivial", so not fixed.  Instead the following updated more_io patch with
    redirty_tail() is merged:
    
    	http://www.spinics.net/linux/lists/linux-ext4/msg04507.html
    
    This will in general prevent 100% on ext2 and possibly other unknown FS bugs.
    Signed-off-by: default avatarWu Fengguang <fengguang.wu@intel.com>
    Cc: Dave Chinner <david@fromorbit.com>
    Cc: Martin Bligh <mbligh@google.com>
    Cc: Michael Rubin <mrubin@google.com>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Christoph Hellwig <hch@infradead.org>
    Cc: Jens Axboe <axboe@kernel.dk>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    a50aeb40
fs-writeback.c 30.8 KB