runtime: madvdontneed documentation is confusing

[Jorropo]

In runtime we can read:

madvdontneed: setting madvdontneed=0 will use MADV_FREE
instead of MADV_DONTNEED on Linux when returning memory to the
kernel. This is more efficient, but means RSS numbers will
drop only when the OS is under memory pressure.

I find the This here very confusing, I read this as madvdontneed=0 (MADV_FREE fast but bad RSS and MADV_DONTNEED slow but accurate) since it's the option explained in the previous sentence while in reality it's speaking about madvdontneed=1.

I belive This should just be replaced with MADV_DONTNEED or DONTNEED.

[ianlancetaylor]

CC @mknyszek

[mknyszek]

I'm not sure I understand your confusion. "This" is indeed referring to madvdontneed=0 as per your original interpretation; MADV_FREE is more efficient, but RSS numbers won't necessarily reflect what's been returned.

Though, I don't have anything against replacing "This" with MADV_FREE either.

[Jorropo]

@mknyszek thx you are right I confused them.
This then make this sentence correct, I don't think it need to be changed.