On Fri, Jun 03, 2011 at 09:12:17AM -0700, Greg Thelen wrote:
> When the system is under background dirty memory threshold but a cgroup
> is over its background dirty memory threshold, then only writeback
> inodes associated with the over-limit cgroup(s).
>
> In addition to checking if the system dirty memory usage is over the
> system background threshold, over_bground_thresh() also checks if any
> cgroups are over their respective background dirty memory thresholds.
> The writeback_control.for_cgroup field is set to distinguish between a
> system and memcg overage.
>
> If performing cgroup writeback, move_expired_inodes() skips inodes that
> do not contribute dirty pages to the cgroup being written back.
>
> After writing some pages, wb_writeback() will call
> mem_cgroup_writeback_done() to update the set of over-bg-limits memcg.
>
> Signed-off-by: Greg Thelen <gthelen@xxxxxxxxxx>
Reviewed-by: Minchan Kim <minchan.kim@xxxxxxxxx>
There are some nitpicks at below.
> ---
> Changelog since v7:
> - over_bground_thresh() now sets shared_inodes=1. In -v7 per memcg
> background writeback did not, so it did not write pages of shared
> inodes in background writeback. In the (potentially common) case
> where the system dirty memory usage is below the system background
> dirty threshold but at least one cgroup is over its background dirty
> limit, then per memcg background writeback is queued for any
> over-background-threshold cgroups. Background writeback should be
> allowed to writeback shared inodes. The hope is that writing such
> inodes has good chance of cleaning the inodes so they can transition
> from shared to non-shared. Such a transition is good because then the
> inode will remain unshared until it is written by multiple cgroup.
> Non-shared inodes offer better isolation.
Above comment should be in description.
>
> fs/fs-writeback.c | 32 ++++++++++++++++++++++++--------
> 1 files changed, 24 insertions(+), 8 deletions(-)
>
> diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
> index 0174fcf..c0bfe62 100644
> --- a/fs/fs-writeback.c
> +++ b/fs/fs-writeback.c
> @@ -256,14 +256,17 @@ static void move_expired_inodes(struct list_head *delaying_queue,
> LIST_HEAD(tmp);
> struct list_head *pos, *node;
> struct super_block *sb = NULL;
> - struct inode *inode;
> + struct inode *inode, *tmp_inode;
> int do_sb_sort = 0;
>
> - while (!list_empty(delaying_queue)) {
> - inode = wb_inode(delaying_queue->prev);
> + list_for_each_entry_safe_reverse(inode, tmp_inode, delaying_queue,
> + i_wb_list) {
> if (wbc->older_than_this &&
> inode_dirtied_after(inode, *wbc->older_than_this))
> break;
> + if (wbc->for_cgroup &&
> + !should_writeback_mem_cgroup_inode(inode, wbc))
> + continue;
> if (sb && sb != inode->i_sb)
> do_sb_sort = 1;
> sb = inode->i_sb;
> @@ -614,14 +617,22 @@ void writeback_inodes_wb(struct bdi_writeback *wb,
> */
> #define MAX_WRITEBACK_PAGES 1024
>
> -static inline bool over_bground_thresh(void)
> +static inline bool over_bground_thresh(struct bdi_writeback *wb,
At present, wb isn't used.
Do you remain it intentionally for using in future?
> + struct writeback_control *wbc)
> {
> unsigned long background_thresh, dirty_thresh;
>
> global_dirty_limits(&background_thresh, &dirty_thresh);
>
> - return (global_page_state(NR_FILE_DIRTY) +
> - global_page_state(NR_UNSTABLE_NFS) > background_thresh);
> + if (global_page_state(NR_FILE_DIRTY) +
> + global_page_state(NR_UNSTABLE_NFS) > background_thresh) {
> + wbc->for_cgroup = 0;
> + return true;
> + }
> +
> + wbc->for_cgroup = 1;
> + wbc->shared_inodes = 1;
> + return mem_cgroups_over_bground_dirty_thresh();
> }
>
> /*
> @@ -700,7 +711,7 @@ static long wb_writeback(struct bdi_writeback *wb,
> * For background writeout, stop when we are below the
> * background dirty threshold
> */
> - if (work->for_background && !over_bground_thresh())
> + if (work->for_background && !over_bground_thresh(wb, &wbc))
> break;
>
> if (work->for_kupdate || work->for_background) {
> @@ -729,6 +740,9 @@ retry:
> work->nr_pages -= write_chunk - wbc.nr_to_write;
> wrote += write_chunk - wbc.nr_to_write;
>
> + if (write_chunk - wbc.nr_to_write > 0)
> + mem_cgroup_writeback_done();
> +
> /*
> * Did we write something? Try for more
> *
> @@ -809,7 +823,9 @@ static unsigned long get_nr_dirty_pages(void)
>
> static long wb_check_background_flush(struct bdi_writeback *wb)
> {
> - if (over_bground_thresh()) {
> + struct writeback_control wbc;
> +
> + if (over_bground_thresh(wb, &wbc)) {
>
> struct wb_writeback_work work = {
> .nr_pages = LONG_MAX,
> --
> 1.7.3.1
>
--
Kind regards
Minchan Kim
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