…key-io#1430)

This update addresses several issues in defrag:
1. In the defrag redesign
(valkey-io#1242), a bug was introduced
where `server.cronloops` was no longer being incremented in the
`whileBlockedCron()`. This resulted in some memory statistics not being
updated while blocked.
2. In the test case for AOF loading, we were seeing errors due to defrag
latencies. However, running the math, the latencies are justified given
the extremely high CPU target of the testcase. Adjusted the expected
latency check to allow longer latencies for this case where defrag is
undergoing starvation while AOF loading is in progress.
3. A "stage" is passed a "target". For the main dictionary and expires,
we were passing in a `kvstore*`. However, on flushall or swapdb, the
pointer may change. It's safer and more stable to use an index for the
DB (a DBID). Then if the pointer changes, we can detect the change, and
simply abort the stage. (If there's still fragmentation to deal with,
we'll pick it up again on the next cycle.)
4. We always start a new stage on a new defrag cycle. This gives the new
stage time to run, and prevents latency issues for certain stages which
don't operate incrementally. However, often several stages will require
almost no work, and this will leave a chunk of our CPU allotment unused.
This is mainly an issue in starvation situations (like AOF loading or
LUA script) - where defrag is running infrequently, with a large
duty-cycle. This change allows a new stage to be initiated if we still
have a standard duty-cycle remaining. (This can happen during starvation
situations where the planned duty cycle is larger than the standard
cycle. Most likely this isn't a concern for real scenarios, but it was
observed in testing.)
5. Minor comment correction in `server.h`

Signed-off-by: Jim Brunner <brunnerj@amazon.com>

…key-io#1430)

This update addresses several issues in defrag:
1. In the defrag redesign
(valkey-io#1242), a bug was introduced
where `server.cronloops` was no longer being incremented in the
`whileBlockedCron()`. This resulted in some memory statistics not being
updated while blocked.
2. In the test case for AOF loading, we were seeing errors due to defrag
latencies. However, running the math, the latencies are justified given
the extremely high CPU target of the testcase. Adjusted the expected
latency check to allow longer latencies for this case where defrag is
undergoing starvation while AOF loading is in progress.
3. A "stage" is passed a "target". For the main dictionary and expires,
we were passing in a `kvstore*`. However, on flushall or swapdb, the
pointer may change. It's safer and more stable to use an index for the
DB (a DBID). Then if the pointer changes, we can detect the change, and
simply abort the stage. (If there's still fragmentation to deal with,
we'll pick it up again on the next cycle.)
4. We always start a new stage on a new defrag cycle. This gives the new
stage time to run, and prevents latency issues for certain stages which
don't operate incrementally. However, often several stages will require
almost no work, and this will leave a chunk of our CPU allotment unused.
This is mainly an issue in starvation situations (like AOF loading or
LUA script) - where defrag is running infrequently, with a large
duty-cycle. This change allows a new stage to be initiated if we still
have a standard duty-cycle remaining. (This can happen during starvation
situations where the planned duty cycle is larger than the standard
cycle. Most likely this isn't a concern for real scenarios, but it was
observed in testing.)
5. Minor comment correction in `server.h`

Signed-off-by: Jim Brunner <brunnerj@amazon.com>