From f814bdda774c183b0cc15ec8f3b6e7c6f4527ba5 Mon Sep 17 00:00:00 2001 From: Jan Kara Date: Tue, 23 Jan 2024 18:58:26 +0100 Subject: blk-wbt: Fix detection of dirty-throttled tasks The detection of dirty-throttled tasks in blk-wbt has been subtly broken since its beginning in 2016. Namely if we are doing cgroup writeback and the throttled task is not in the root cgroup, balance_dirty_pages() will set dirty_sleep for the non-root bdi_writeback structure. However blk-wbt checks dirty_sleep only in the root cgroup bdi_writeback structure. Thus detection of recently throttled tasks is not working in this case (we noticed this when we switched to cgroup v2 and suddently writeback was slow). Since blk-wbt has no easy way to get to proper bdi_writeback and furthermore its intention has always been to work on the whole device rather than on individual cgroups, just move the dirty_sleep timestamp from bdi_writeback to backing_dev_info. That fixes the checking for recently throttled task and saves memory for everybody as a bonus. CC: stable@vger.kernel.org Fixes: b57d74aff9ab ("writeback: track if we're sleeping on progress in balance_dirty_pages()") Signed-off-by: Jan Kara Link: https://lore.kernel.org/r/20240123175826.21452-1-jack@suse.cz [axboe: fixup indentation errors] Signed-off-by: Jens Axboe --- include/linux/backing-dev-defs.h | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) (limited to 'include') diff --git a/include/linux/backing-dev-defs.h b/include/linux/backing-dev-defs.h index ae12696ec492..2ad261082bba 100644 --- a/include/linux/backing-dev-defs.h +++ b/include/linux/backing-dev-defs.h @@ -141,8 +141,6 @@ struct bdi_writeback { struct delayed_work dwork; /* work item used for writeback */ struct delayed_work bw_dwork; /* work item used for bandwidth estimate */ - unsigned long dirty_sleep; /* last wait */ - struct list_head bdi_node; /* anchored at bdi->wb_list */ #ifdef CONFIG_CGROUP_WRITEBACK @@ -179,6 +177,11 @@ struct backing_dev_info { * any dirty wbs, which is depended upon by bdi_has_dirty(). */ atomic_long_t tot_write_bandwidth; + /* + * Jiffies when last process was dirty throttled on this bdi. Used by + * blk-wbt. + */ + unsigned long last_bdp_sleep; struct bdi_writeback wb; /* the root writeback info for this bdi */ struct list_head wb_list; /* list of all wbs */ -- cgit