From a035bff6b82aca89c1223e2c614adc2d17ec8aa2 Mon Sep 17 00:00:00 2001 From: Sunil Mushran Date: Sun, 24 Jul 2011 10:35:54 -0700 Subject: [PATCH] ocfs2: Add comment about orphan scanning Add a comment that explains the reason as to why orphan scan scans all the slots. Signed-off-by: Sunil Mushran --- fs/ocfs2/journal.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/fs/ocfs2/journal.c b/fs/ocfs2/journal.c index 8eaaa7854409..0a42ae96dca7 100644 --- a/fs/ocfs2/journal.c +++ b/fs/ocfs2/journal.c @@ -1811,6 +1811,20 @@ static inline unsigned long ocfs2_orphan_scan_timeout(void) * every slot, queuing a recovery of the slot on the ocfs2_wq thread. This * is done to catch any orphans that are left over in orphan directories. * + * It scans all slots, even ones that are in use. It does so to handle the + * case described below: + * + * Node 1 has an inode it was using. The dentry went away due to memory + * pressure. Node 1 closes the inode, but it's on the free list. The node + * has the open lock. + * Node 2 unlinks the inode. It grabs the dentry lock to notify others, + * but node 1 has no dentry and doesn't get the message. It trylocks the + * open lock, sees that another node has a PR, and does nothing. + * Later node 2 runs its orphan dir. It igets the inode, trylocks the + * open lock, sees the PR still, and does nothing. + * Basically, we have to trigger an orphan iput on node 1. The only way + * for this to happen is if node 1 runs node 2's orphan dir. + * * ocfs2_queue_orphan_scan gets called every ORPHAN_SCAN_SCHEDULE_TIMEOUT * seconds. It gets an EX lock on os_lockres and checks sequence number * stored in LVB. If the sequence number has changed, it means some other