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writeback: Avoid softlockup when switching many inodes 

process_inode_switch_wbs_work() can be switching over 100 inodes to a
different cgroup. Since switching an inode requires counting all dirty &
under-writeback pages in the address space of each inode, this can take
a significant amount of time. Add a possibility to reschedule after
processing each inode to avoid softlockups.

Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>
This commit is contained in:
Jan Kara 2025-09-12 12:38:36 +02:00 committed by Christian Brauner
parent e1b849cfa6
commit 66c14dccd8
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GPG Key ID: 91C61BC06578DCA2
1 changed files with 10 additions and 1 deletions
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11
fs/fs-writeback.c
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@ -500,6 +500,7 @@ static void process_inode_switch_wbs(struct bdi_writeback *new_wb,
*/
down_read(&bdi->wb_switch_rwsem);
inodep = isw->inodes;
/*
* By the time control reaches here, RCU grace period has passed
* since I_WB_SWITCH assertion and all wb stat update transactions
@ -510,6 +511,7 @@ static void process_inode_switch_wbs(struct bdi_writeback *new_wb,
* gives us exclusion against all wb related operations on @inode
* including IO list manipulations and stat updates.
*/
relock:
if (old_wb < new_wb) {
spin_lock(&old_wb->list_lock);
spin_lock_nested(&new_wb->list_lock, SINGLE_DEPTH_NESTING);
@ -518,10 +520,17 @@ static void process_inode_switch_wbs(struct bdi_writeback *new_wb,
spin_lock_nested(&old_wb->list_lock, SINGLE_DEPTH_NESTING);
}
for (inodep = isw->inodes; *inodep; inodep++) {
while (*inodep) {
WARN_ON_ONCE((*inodep)->i_wb != old_wb);
if (inode_do_switch_wbs(*inodep, old_wb, new_wb))
nr_switched++;
inodep++;
if (*inodep && need_resched()) {
spin_unlock(&new_wb->list_lock);
spin_unlock(&old_wb->list_lock);
cond_resched();
goto relock;
}
}
spin_unlock(&new_wb->list_lock);