The max_seq and active reader mechanisms in the item cache stop readers
from reading old items and inserting them in the cache after newer items
have been reclaimed by memory pressure. The max_seq field in the pages
must reflect the greatest seq of the items in the page so that reclaim
knows that the page contains items newer than old readers and must not
be removed.
We update the page max_seq as items are inserted or as they're dirtied
in the page. There's an additional subtle effect that the max_seq can
also protect items which have been erased. Deletion items are erased
from the pages as a commit completes. The max_seq in that page will
still protect it from being reclaimed even though no items have that seq
value themselves.
That protection fails if the range of keys containing the erased item is
moved to another page with a lower max_seq. The item mover only
updated the destination page's max_seq for each item that was moved. It
missed that the empty space between the items might have a larger
max_seq from an erased item. We don't know where the erased item is so
we have to assume that a larger max_seq in the source page must be set
on the destination page.
This could explain very rare item cache corruption where nodes were
seeing deleted directory entry items reappearing. It would take a
specific sequence of events involving large directories with an isolated
removal, a delayed item cache reader, a commit, and then enough
insertions to split the page all happening in precisely the wrong
sequence.
Signed-off-by: Zach Brown <zab@versity.com>
Add a command to change the quorum config which starts by only supports
updating the super block whlie the file system is oflfine.
Signed-off-by: Zach Brown <zab@versity.com>
Let's try maintaining release notes in a file in the repo. There are
lots of schemes for associating commits and release notes and this seems
like the simplest place to start.
Signed-off-by: Zach Brown <zab@versity.com>
