From: Roman Gushchin <guro@xxxxxx> Subject: writeback, cgroup: keep list of inodes attached to bdi_writeback Currently there is no way to iterate over inodes attached to a specific cgwb structure. It limits the ability to efficiently reclaim the writeback structure itself and associated memory and block cgroup structures without scanning all inodes belonging to a sb, which can be prohibitively expensive. While dirty/in-active-writeback an inode belongs to one of the bdi_writeback's io lists: b_dirty, b_io, b_more_io and b_dirty_time. Once cleaned up, it's removed from all io lists. So the inode->i_io_list can be reused to maintain the list of inodes, attached to a bdi_writeback structure. This patch introduces a new wb->b_attached list, which contains all inodes which were dirty at least once and are attached to the given cgwb. Inodes attached to the root bdi_writeback structures are never placed on such list. The following patch will use this list to try to release cgwbs structures more efficiently. Link: https://lkml.kernel.org/r/20210608230225.2078447-6-guro@xxxxxx Signed-off-by: Roman Gushchin <guro@xxxxxx> Suggested-by: Jan Kara <jack@xxxxxxx> Reviewed-by: Jan Kara <jack@xxxxxxx> Acked-by: Tejun Heo <tj@xxxxxxxxxx> Acked-by: Dennis Zhou <dennis@xxxxxxxxxx> Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx> Cc: Dave Chinner <dchinner@xxxxxxxxxx> Cc: Jan Kara <jack@xxxxxxxx> Cc: Jens Axboe <axboe@xxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- fs/fs-writeback.c | 93 ++++++++++++++++++----------- include/linux/backing-dev-defs.h | 1 mm/backing-dev.c | 2 3 files changed, 62 insertions(+), 34 deletions(-) --- a/fs/fs-writeback.c~writeback-cgroup-keep-list-of-inodes-attached-to-bdi_writeback +++ a/fs/fs-writeback.c @@ -131,25 +131,6 @@ static bool inode_io_list_move_locked(st return false; } -/** - * inode_io_list_del_locked - remove an inode from its bdi_writeback IO list - * @inode: inode to be removed - * @wb: bdi_writeback @inode is being removed from - * - * Remove @inode which may be on one of @wb->b_{dirty|io|more_io} lists and - * clear %WB_has_dirty_io if all are empty afterwards. - */ -static void inode_io_list_del_locked(struct inode *inode, - struct bdi_writeback *wb) -{ - assert_spin_locked(&wb->list_lock); - assert_spin_locked(&inode->i_lock); - - inode->i_state &= ~I_SYNC_QUEUED; - list_del_init(&inode->i_io_list); - wb_io_lists_depopulated(wb); -} - static void wb_wakeup(struct bdi_writeback *wb) { spin_lock_bh(&wb->work_lock); @@ -279,6 +260,28 @@ void __inode_attach_wb(struct inode *ino EXPORT_SYMBOL_GPL(__inode_attach_wb); /** + * inode_cgwb_move_to_attached - put the inode onto wb->b_attached list + * @inode: inode of interest with i_lock held + * @wb: target bdi_writeback + * + * Remove the inode from wb's io lists and if necessarily put onto b_attached + * list. Only inodes attached to cgwb's are kept on this list. + */ +static void inode_cgwb_move_to_attached(struct inode *inode, + struct bdi_writeback *wb) +{ + assert_spin_locked(&wb->list_lock); + assert_spin_locked(&inode->i_lock); + + inode->i_state &= ~I_SYNC_QUEUED; + if (wb != &wb->bdi->wb) + list_move(&inode->i_io_list, &wb->b_attached); + else + list_del_init(&inode->i_io_list); + wb_io_lists_depopulated(wb); +} + +/** * locked_inode_to_wb_and_lock_list - determine a locked inode's wb and lock it * @inode: inode of interest with i_lock held * @@ -418,21 +421,28 @@ static void inode_switch_wbs_work_fn(str wb_get(new_wb); /* - * Transfer to @new_wb's IO list if necessary. The specific list - * @inode was on is ignored and the inode is put on ->b_dirty which - * is always correct including from ->b_dirty_time. The transfer - * preserves @inode->dirtied_when ordering. + * Transfer to @new_wb's IO list if necessary. If the @inode is dirty, + * the specific list @inode was on is ignored and the @inode is put on + * ->b_dirty which is always correct including from ->b_dirty_time. + * The transfer preserves @inode->dirtied_when ordering. If the @inode + * was clean, it means it was on the b_attached list, so move it onto + * the b_attached list of @new_wb. */ if (!list_empty(&inode->i_io_list)) { - struct inode *pos; - - inode_io_list_del_locked(inode, old_wb); inode->i_wb = new_wb; - list_for_each_entry(pos, &new_wb->b_dirty, i_io_list) - if (time_after_eq(inode->dirtied_when, - pos->dirtied_when)) - break; - inode_io_list_move_locked(inode, new_wb, pos->i_io_list.prev); + + if (inode->i_state & I_DIRTY_ALL) { + struct inode *pos; + + list_for_each_entry(pos, &new_wb->b_dirty, i_io_list) + if (time_after_eq(inode->dirtied_when, + pos->dirtied_when)) + break; + inode_io_list_move_locked(inode, new_wb, + pos->i_io_list.prev); + } else { + inode_cgwb_move_to_attached(inode, new_wb); + } } else { inode->i_wb = new_wb; } @@ -1021,6 +1031,17 @@ fs_initcall(cgroup_writeback_init); static void bdi_down_write_wb_switch_rwsem(struct backing_dev_info *bdi) { } static void bdi_up_write_wb_switch_rwsem(struct backing_dev_info *bdi) { } +static void inode_cgwb_move_to_attached(struct inode *inode, + struct bdi_writeback *wb) +{ + assert_spin_locked(&wb->list_lock); + assert_spin_locked(&inode->i_lock); + + inode->i_state &= ~I_SYNC_QUEUED; + list_del_init(&inode->i_io_list); + wb_io_lists_depopulated(wb); +} + static struct bdi_writeback * locked_inode_to_wb_and_lock_list(struct inode *inode) __releases(&inode->i_lock) @@ -1121,7 +1142,11 @@ void inode_io_list_del(struct inode *ino wb = inode_to_wb_and_lock_list(inode); spin_lock(&inode->i_lock); - inode_io_list_del_locked(inode, wb); + + inode->i_state &= ~I_SYNC_QUEUED; + list_del_init(&inode->i_io_list); + wb_io_lists_depopulated(wb); + spin_unlock(&inode->i_lock); spin_unlock(&wb->list_lock); } @@ -1434,7 +1459,7 @@ static void requeue_inode(struct inode * inode->i_state &= ~I_SYNC_QUEUED; } else { /* The inode is clean. Remove from writeback lists. */ - inode_io_list_del_locked(inode, wb); + inode_cgwb_move_to_attached(inode, wb); } } @@ -1586,7 +1611,7 @@ static int writeback_single_inode(struct * responsible for the writeback lists. */ if (!(inode->i_state & I_DIRTY_ALL)) - inode_io_list_del_locked(inode, wb); + inode_cgwb_move_to_attached(inode, wb); spin_unlock(&wb->list_lock); inode_sync_complete(inode); out: --- a/include/linux/backing-dev-defs.h~writeback-cgroup-keep-list-of-inodes-attached-to-bdi_writeback +++ a/include/linux/backing-dev-defs.h @@ -154,6 +154,7 @@ struct bdi_writeback { struct cgroup_subsys_state *blkcg_css; /* and blkcg */ struct list_head memcg_node; /* anchored at memcg->cgwb_list */ struct list_head blkcg_node; /* anchored at blkcg->cgwb_list */ + struct list_head b_attached; /* attached inodes, protected by list_lock */ union { struct work_struct release_work; --- a/mm/backing-dev.c~writeback-cgroup-keep-list-of-inodes-attached-to-bdi_writeback +++ a/mm/backing-dev.c @@ -396,6 +396,7 @@ static void cgwb_release_workfn(struct w fprop_local_destroy_percpu(&wb->memcg_completions); percpu_ref_exit(&wb->refcnt); wb_exit(wb); + WARN_ON_ONCE(!list_empty(&wb->b_attached)); kfree_rcu(wb, rcu); } @@ -472,6 +473,7 @@ static int cgwb_create(struct backing_de wb->memcg_css = memcg_css; wb->blkcg_css = blkcg_css; + INIT_LIST_HEAD(&wb->b_attached); INIT_WORK(&wb->release_work, cgwb_release_workfn); set_bit(WB_registered, &wb->state); _
