On 03/08/2013 02:27 PM, Dave Chinner wrote:
> On Fri, Mar 08, 2013 at 10:43:00AM +0800, Yan, Zheng wrote:
>> On 03/08/2013 10:04 AM, Dave Chinner wrote:
>>> On Thu, Mar 07, 2013 at 07:37:36PM +0800, Yan, Zheng wrote:
>>>> From: "Yan, Zheng" <[email protected]>
>>>>
>>>> dentry_lru_prune() should always call file system's d_prune callback.
>>>
>>> Why? What bug does this fix?
>>>
>>
>> Ceph uses a flag to track if the dcache contents for a directory are
>> complete,
>> and it relies on d_prune() to clear the flag when some dentries are trimmed.
>> We noticed that dentry_lru_prune() sometimes does not call ceph_d_prune().
>> It seems the dentry in question is ancestor trimmed by
>> try_prune_one_dentry().
>
> That doesn't sound right to me. Any dentry that goes through
> try_prune_one_dentry() is on a LRU list, and will end up in
> dentry_kill() if the reference count drops to zero and hence calls
> dentry_lru_prune() with a non-emtpy LRU pointer.
>
> If it has a non-zero reference count, it gets removed from the LRU,
> and the next call to dput() that drops the reference count to zero
> will add it back to the LRU and it will go around again. So it
> sounds to me like there is something else going on here.
>
> FWIW, if the dentry is not on the LRU, why would it need pruning?
> If it needs pruning regardless of it's status on the LRU, then
> dentry_lru_prune() should go away entirely and pruning be done
> explicity where it is needed rather than wrapped up in an unrelated
> LRU operation....
>
I didn't described it clearly
static void try_prune_one_dentry(struct dentry *dentry)
__releases(dentry->d_lock)
{
.....
/* Prune ancestors. */
dentry = parent;
while (dentry) {
spin_lock(&dentry->d_lock);
if (dentry->d_count > 1) {
dentry->d_count--;
spin_unlock(&dentry->d_lock);
return;
}
dentry = dentry_kill(dentry, 1);
~~~~I mean dentries that are pruned here~~~~
}
}
Regards
Yan, Zheng
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