Re: Possible error in fs/buffer.c

[Andrew Morton <akpm@osdl.org>]

"Robert W. Maloy" <r.w.maloy@acm.org> wrote:
>
> 	While code surfing I found what appears to be a problem with the 
> following code in fs/buffer.c {function mark_buffer_inode_dirty}: 
> 
>        if (list_empty(&bh->b_assoc_buffers))
>                 buffer_insert_list(&buffer_mapping->private_lock,
>                                 bh, &mapping->private_list);

This is saying "is the buffer is not on any list, then place it on the
mapping's list now.  If the buffer _is_ already on some list then we know
it must already be on mapping->private_list, so we have nothing to do".

Re-dirtying an already-dirty buffer is an extremely common case, and here
we look for an opportunity to avoid dirtying a cacheline or two.