util/mon: pass reserved account by reference

[yuzefovich]

util/mon: pass reserved account by reference

This commit makes it so that we now pass the reserved memory account
when starting up memory monitors by reference. Previously, due to
passing by value, when the monitor is stopped, the copy of the value
would get used so that the actual "reserved" memory account would get
out of sync with its user. This is now fixed. However, this bug doesn't
really have any production impact since we use this "reserved" feature
in a handful of places and these "reserved" memory accounts are not
reused between different usages.

Additionally, this commit renames MakeStandaloneBudget to
NewStandaloneBudget (since it now returns a reference) and adds
a separate "start" method when the caller doesn't want to pre-reserve
anything when starting up a monitor.

Release note: None

sql: make sure to close the reserved account for each session

This commit makes it more clear that the "reserved" memory account
created for each connection is closed when that connection is closed.
Previously, the account was already cleared (when "session root" monitor
is stopped which happens when the connExecutor stops), so there was no
leak in the accounting system because of it, yet it wasn't obvious - this
commit makes it more obvious.

Release note: None

[cockroach-teamcity]

This change is 

[knz]

with tip

Reviewed 57 of 57 files at r1, 2 of 2 files at r2, all commit messages.
Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @michae2 and @yuzefovich)

---

pkg/sql/conn_executor.go line 760 at r2 (raw file):

		// also cannot close it before closeWrapper since we need to close the
		// internal monitors of the connExecutor first.
		defer reserved.Close(ctx)

1. if you pull the defer out of the closure, you'll save some bytes.

defer reserved.Close(ctx)
defer func() { ... }()
return h.ex.run

2. you can save the entire allocation by passing the outer variables as arg:

defer func(ctx context.Context, h ConnectionHandler) {...} (ctx, h)

[yuzefovich]

TFTR!

bors r+

Reviewable status: complete! 0 of 0 LGTMs obtained (and 1 stale) (waiting on @knz and @michae2)

---

pkg/sql/conn_executor.go line 760 at r2 (raw file):

Previously, knz (kena) wrote…

1. if you pull the defer out of the closure, you'll save some bytes.

defer reserved.Close(ctx)
defer func() { ... }()
return h.ex.run

2. you can save the entire allocation by passing the outer variables as arg:

defer func(ctx context.Context, h ConnectionHandler) {...} (ctx, h)

Done.

[craig]

Build failed (retrying...):

• GitHub CI (Cockroach)

[craig]

Build succeeded:

• GitHub CI (Cockroach)