Zach Brown 5f682dabb5 Item cache invalidation uses seqs to avoid readers ...

The item cache has to be careful not to insert stale read items when
previously dirty items have been written and invalidated while a read
was in flight.

This was previously done by recording the possible range of items that a
reader could see based on the key range of its lock.   This is
disasterous when a workload operates entirely within one lock.  I ran
into this when testing a small number of files with massive amounts of
xattrs.  While any reader is in flight all pages can't be invalidated
because they all intersect with the one lock that covers all the items
in use.

The fix is to more naturally reflect the problem by tracking the
greatest item seq in pages and the earliest seq that any readers
can't see.  This lets invalidate only skip pages with items
that weren't visible to the earliest reader.

This more naturally reflects that the problem is due to the age of the
items, not their position in the key space.  Now only a few of the most
recently modified pages could be skipped and they'll be at the end
of the LRU and won't typically be visited.  As an added benefit it's
now much cheaper to add, delete, and test the active readers.

This fix stopped rm -rf of a full system's worth of xattrs from taking
minutes constantly spinning skipping all pages in the LRU to seconds of
doing real removal work.

Signed-off-by: Zach Brown <zab@versity.com>

2021-07-07 14:13:14 -07:00

..

src

Item cache invalidation uses seqs to avoid readers

2021-07-07 14:13:14 -07:00

.gitignore

scoutfs: update rpm building infrastructure

2018-09-14 15:07:10 -07:00

Makefile

Filesystem version instead of format hash check

2021-01-15 10:53:00 -08:00

scoutfs-kmod.spec.in

scoutfs: update rpm building infrastructure

2018-09-14 15:07:10 -07:00