diff options
Diffstat (limited to 'fs/fs-writeback.c')
-rw-r--r-- | fs/fs-writeback.c | 117 |
1 files changed, 111 insertions, 6 deletions
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c index f67b956..08f5496 100644 --- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -308,6 +308,115 @@ static struct bdi_writeback *inode_to_wb_and_lock_list(struct inode *inode) return locked_inode_to_wb_and_lock_list(inode); } +struct inode_switch_wbs_context { + struct inode *inode; + struct bdi_writeback *new_wb; + + struct rcu_head rcu_head; + struct work_struct work; +}; + +static void inode_switch_wbs_work_fn(struct work_struct *work) +{ + struct inode_switch_wbs_context *isw = + container_of(work, struct inode_switch_wbs_context, work); + struct inode *inode = isw->inode; + struct bdi_writeback *new_wb = isw->new_wb; + + /* + * By the time control reaches here, RCU grace period has passed + * since I_WB_SWITCH assertion and all wb stat update transactions + * between unlocked_inode_to_wb_begin/end() are guaranteed to be + * synchronizing against mapping->tree_lock. + */ + spin_lock(&inode->i_lock); + + inode->i_wb_frn_winner = 0; + inode->i_wb_frn_avg_time = 0; + inode->i_wb_frn_history = 0; + + /* + * Paired with load_acquire in unlocked_inode_to_wb_begin() and + * ensures that the new wb is visible if they see !I_WB_SWITCH. + */ + smp_store_release(&inode->i_state, inode->i_state & ~I_WB_SWITCH); + + spin_unlock(&inode->i_lock); + + iput(inode); + wb_put(new_wb); + kfree(isw); +} + +static void inode_switch_wbs_rcu_fn(struct rcu_head *rcu_head) +{ + struct inode_switch_wbs_context *isw = container_of(rcu_head, + struct inode_switch_wbs_context, rcu_head); + + /* needs to grab bh-unsafe locks, bounce to work item */ + INIT_WORK(&isw->work, inode_switch_wbs_work_fn); + schedule_work(&isw->work); +} + +/** + * inode_switch_wbs - change the wb association of an inode + * @inode: target inode + * @new_wb_id: ID of the new wb + * + * Switch @inode's wb association to the wb identified by @new_wb_id. The + * switching is performed asynchronously and may fail silently. + */ +static void inode_switch_wbs(struct inode *inode, int new_wb_id) +{ + struct backing_dev_info *bdi = inode_to_bdi(inode); + struct cgroup_subsys_state *memcg_css; + struct inode_switch_wbs_context *isw; + + /* noop if seems to be already in progress */ + if (inode->i_state & I_WB_SWITCH) + return; + + isw = kzalloc(sizeof(*isw), GFP_ATOMIC); + if (!isw) + return; + + /* find and pin the new wb */ + rcu_read_lock(); + memcg_css = css_from_id(new_wb_id, &memory_cgrp_subsys); + if (memcg_css) + isw->new_wb = wb_get_create(bdi, memcg_css, GFP_ATOMIC); + rcu_read_unlock(); + if (!isw->new_wb) + goto out_free; + + /* while holding I_WB_SWITCH, no one else can update the association */ + spin_lock(&inode->i_lock); + if (inode->i_state & (I_WB_SWITCH | I_FREEING) || + inode_to_wb(inode) == isw->new_wb) { + spin_unlock(&inode->i_lock); + goto out_free; + } + inode->i_state |= I_WB_SWITCH; + spin_unlock(&inode->i_lock); + + ihold(inode); + isw->inode = inode; + + /* + * In addition to synchronizing among switchers, I_WB_SWITCH tells + * the RCU protected stat update paths to grab the mapping's + * tree_lock so that stat transfer can synchronize against them. + * Let's continue after I_WB_SWITCH is guaranteed to be visible. + */ + call_rcu(&isw->rcu_head, inode_switch_wbs_rcu_fn); + return; + +out_free: + if (isw->new_wb) + wb_put(isw->new_wb); + kfree(isw); +} + /** * wbc_attach_and_unlock_inode - associate wbc with target inode and unlock it * @wbc: writeback_control of interest @@ -433,12 +542,8 @@ void wbc_detach_inode(struct writeback_control *wbc) * is okay. The main goal is avoiding keeping an inode on * the wrong wb for an extended period of time. */ - if (hweight32(history) > WB_FRN_HIST_THR_SLOTS) { - /* switch */ - max_id = 0; - avg_time = 0; - history = 0; - } + if (hweight32(history) > WB_FRN_HIST_THR_SLOTS) + inode_switch_wbs(inode, max_id); } /* |