Re: [GIT PULL] MM updates for 6.4-rc1

From: Linus Torvalds <torvalds@linux-foundation.org>
To: Suren Baghdasaryan <surenb@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	mm-commits@vger.kernel.org, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org,
	Lorenzo Stoakes <lstoakes@gmail.com>,
	Vlastimil Babka <vbabka@suse.cz>
Subject: Re: [GIT PULL] MM updates for 6.4-rc1
Date: Fri, 28 Apr 2023 09:08:21 -0700	[thread overview]
Message-ID: <CAHk-=wg0SyFDp_sdcEH-D+LNxuzL_dWA1vZEowUN16n_+yRHPQ@mail.gmail.com> (raw)
In-Reply-To: <CAJuCfpHZSEjG2nti5iWbPQjWgXcHZ95hFS2FKwaPC-sZPdSznw@mail.gmail.com>

On Fri, Apr 28, 2023 at 9:03 AM Suren Baghdasaryan <surenb@google.com> wrote:
>
> I wanted these stats enabled by default to be able to identify
> possible pathological cases and to also let users disable them if they
> can't tolerate even a small overhead in the pagefault path. Should I
> document this reasoning for the config option?

You should document what the stats actually count (at a high enough
level for a user to understand), and why anybody would want to keep
them on.

Honestly, 99% of the time, these are things that *developers* think
they might want, but that nobody else will ever ever use.

Really, ask yourself if a normal user would ever look at them?

Now, ask yourself whether this might be something that a cloud
provider would want to look at to gather statistics.

And if it's the latter case, then it should be "default n", because
the default should be for the people who DO NOT KNOW, AND DO NOT CARE.

The cloud provider will be using a custom config anyway. The default
is irrelevant for that use. The use that *matters* is literally the
clueless end user who I bet will never look at these numbers, and will
never be asked for them.

               Linus