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ocfs2: Add comment about orphan scanning

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Add a comment that explains the reason as to why orphan scan scans all the slots.

Signed-off-by: Sunil Mushran <sunil.mushran@oracle.com>
This commit is contained in:
Sunil Mushran 2011-07-24 10:35:54 -07:00
parent 619c200de1
commit a035bff6b8
1 changed files with 14 additions and 0 deletions
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14
fs/ocfs2/journal.c
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@ -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