> On 17 May 2020, at 10:55, Andreas Dilger <adilger@xxxxxxxxx> wrote:
>
> The question is whether this is situation is affecting only a few inode
> allocations for a short time after mount, or does this persist for a long
> time? I think that it _should_ be only a short time, because these other
> threads should all start prefetch on their preferred groups, so even if a
> few inodes have their blocks allocated in the "wrong" group, it shouldn't
> be a long term problem since the prefetched bitmaps will finish loading
> and allow the blocks to be allocated, or skipped if group is fragmented.
Yes, that’s the idea - there is a short window when buddy data is being
populated. And for each “cluster” (not just a single group) prefetching
will be initiated by allocation.
It’s possible that some number of inodes will get “bad” blocks right after
after mount.
If you think this is a bad scenario I can introduce couple more things:
1) few times discussed prefetching thread
2) let mballoc wait for the goal group to get ready - this essentials one
more check in ext4_mb_good_group()
Thanks, Alex
