Re: [PATCH] Stop searching for free slots in an inode chunk when there are none

Carlos Eduardo Maiolino
2017-08-04T08:55:28Z

Hi Dave.

> > Add a way to stop the loop when a free slot is not found in the btree,
> > making the function to fall into the whole AG scan which will then, be
> > able to detect the corruption and shut the filesystem down.
>
> That doesn't sound quite right. The initial scan and the restart
> loop are both limited to scanning search_distance records - we never
> search the entire tree except when it's really small (i..e less than
> 10-20 records (640-1280 inodes) depending on balance). If the
> pagino record to end of btree distance in both directions is shorter
> than the search distance for a given loop (i.e. less than 10 records
> from pagino to end-of-btree) then that is the only time a corrupted
> agi->freecount can cause this problem.
>

I agree with you, but still, we are feasible to have this corruption happening,
and I've seen reports of users hitting it.

> IOWs, on production systems where there's more than a few hundred
> inodes (i.e. the vast majority of installations) a corrupted
> agi->freecount won't lead to a endless loop because search_distance
> will terminate the retry loop and we'll allocate a new inode.
>
> To tell the truth, I'd much rather we just use the search distance
> to prevent endless looping than add a second method of limiting
> the search loop. i.e. don't reset search_distance when we restart
> the search loop at pagino. That means even for small trees (<
> search_distance * 2 records) we'll retry when we get to the end of
> tree, but we'll still break out of the loop and allocate new inodes
> as soon as we hit the search distance limit.
>

Sounds reasonable, I'll try that and send a V2,

Thank you!!

--
--Carlos