On Fri 26-02-16 08:46:25, Yang Shi wrote:
> The list_lock was moved outside the for loop by commit
> e8dfc30582995ae12454cda517b17d6294175b07 ("writeback: elevate queue_io()
> into wb_writeback())", however, the commit log says "No behavior change", so
> it sounds safe to have the list_lock acquired inside the for loop as it did
> before.
> Leave tracepoints outside the critical area since tracepoints already have
> preempt disabled.The patch says what but it completely misses the why part. > > Signed-off-by: Yang Shi <[email protected]> > --- > Tested with ltp on 8 cores Cortex-A57 machine. > > fs/fs-writeback.c | 12 +++++++----- > 1 file changed, 7 insertions(+), 5 deletions(-) > > diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c > index 1f76d89..9b7b5f6 100644 > --- a/fs/fs-writeback.c > +++ b/fs/fs-writeback.c > @@ -1623,7 +1623,6 @@ static long wb_writeback(struct bdi_writeback *wb, > work->older_than_this = &oldest_jif; > > blk_start_plug(&plug); > - spin_lock(&wb->list_lock); > for (;;) { > /* > * Stop writeback when nr_pages has been consumed > @@ -1661,15 +1660,19 @@ static long wb_writeback(struct bdi_writeback *wb, > oldest_jif = jiffies; > > trace_writeback_start(wb, work); > + > + spin_lock(&wb->list_lock); > if (list_empty(&wb->b_io)) > queue_io(wb, work); > if (work->sb) > progress = writeback_sb_inodes(work->sb, wb, work); > else > progress = __writeback_inodes_wb(wb, work); > - trace_writeback_written(wb, work); > > wb_update_bandwidth(wb, wb_start); > + spin_unlock(&wb->list_lock); > + > + trace_writeback_written(wb, work); > > /* > * Did we write something? Try for more > @@ -1693,15 +1696,14 @@ static long wb_writeback(struct bdi_writeback *wb, > */ > if (!list_empty(&wb->b_more_io)) { > trace_writeback_wait(wb, work); > + spin_lock(&wb->list_lock); > inode = wb_inode(wb->b_more_io.prev); > - spin_lock(&inode->i_lock); > spin_unlock(&wb->list_lock); > + spin_lock(&inode->i_lock); > /* This function drops i_lock... */ > inode_sleep_on_writeback(inode); > - spin_lock(&wb->list_lock); > } > } > - spin_unlock(&wb->list_lock); > blk_finish_plug(&plug); > > return nr_pages - work->nr_pages; > -- > 2.0.2 > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to [email protected]. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: <a href=mailto:"[email protected]";> [email protected] </a> -- Michal Hocko SUSE Labs
