This recently came up again. It seems that `+RTS -h -i0` will just turn every minor collection into a major one: https://gitlab.haskell.org/ghc/ghc/issues/17387#note_248705
`-i0` seems significantly different from `-i0.001`, say, in that it just turns minor GCs into major ones and doesn't introduce non-determinism otherwise. Sampling rate can be controlled with `-A`, much like `-F1` (but it's still faster for some reason).

Am Mo., 10. Dez. 2018 um 09:11 Uhr schrieb Simon Marlow <marlowsd@gmail.com>:
https://phabricator.haskell.org/D5428


On Sun, 9 Dec 2018 at 10:12, Sebastian Graf <sgraf1337@gmail.com> wrote:
Ah, I was only looking at `+RTS --help`, not the users guide. Silly me.

Am Do., 6. Dez. 2018 um 20:53 Uhr schrieb Simon Marlow <marlowsd@gmail.com>:

On Thu, 6 Dec 2018 at 16:21, Sebastian Graf <sgraf1337@gmail.com> wrote:
Hey,

thanks, all! Measuring with `-A1M -F1` delivers much more reliable residency numbers.
`-F` doesn't seem to be documented. From reading `rts/RtsFlags.c` and `rts/sm/GC.c` I gather that it's the factor by which to multiply the number of live bytes by to get the new old gen size?
So effectively, the old gen will 'overflow' on every minor GC, neat!

Greetings
Sebastian

Am Do., 6. Dez. 2018 um 12:52 Uhr schrieb Simon Peyton Jones via ghc-devs <ghc-devs@haskell.org>:
|  Right. A parameter for fixing the nursery size would be easy to implement,
|  I think. Just a new flag, then in GC.c:resize_nursery() use the flag as the
|  nursery size.

Super!  That would be v useful.

|  "Max. residency" is really hard to measure (need to do very frequent GCs),
|  perhaps a better question to ask is "residency when the program is in state
|  S".

Actually, Sebastian simply wants to see an accurate, reproducible residency profile, and doing frequent GCs might well be an acceptable cost. 

Simon
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