| Message ID | 1456505185-21566-1-git-send-email-yang.shi@linaro.org |
|---|---|
| State | New |
| Headers | show |
On 2/29/2016 7:06 AM, Michal Hocko wrote: > 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. I'm just wondering the finer grained lock may reach a little better performance, i.e. more likely for preempt, lower latency. Thanks, Yang > >> >> Signed-off-by: Yang Shi <yang.shi@linaro.org> >> --- >> 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 majordomo@kvack.org. For more info on Linux MM, >> see: http://www.linux-mm.org/ . >> Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a> >
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;
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. Signed-off-by: Yang Shi <yang.shi@linaro.org> --- Tested with ltp on 8 cores Cortex-A57 machine. fs/fs-writeback.c | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-) -- 2.0.2