Re: [PATCH v2 5/6] alloc_tag: make page allocation tag reference size configurable

Andrew Morton
2024-09-02T05:09:33Z

On Sun, 1 Sep 2024 21:41:27 -0700 Suren Baghdasaryan <surenb@google.com> wrote:

> Introduce CONFIG_PGALLOC_TAG_REF_BITS to control the size of the
> page allocation tag references. When the size is configured to be
> less than a direct pointer, the tags are searched using an index
> stored as the tag reference.
>
> ...
>
> +config PGALLOC_TAG_REF_BITS
> + int "Number of bits for page allocation tag reference (10-64)"
> + range 10 64
> + default "64"
> + depends on MEM_ALLOC_PROFILING
> + help
> + Number of bits used to encode a page allocation tag reference.
> +
> + Smaller number results in less memory overhead but limits the number of
> + allocations which can be tagged (including allocations from modules).
> +

In other words, "we have no idea what's best for you, you're on your
own".

I pity our poor users.

Can we at least tell them what they should look at to determine whether
whatever random number they chose was helpful or harmful?