Re: [PATCH bpf-next v3 2/6] mm, bpf: Introduce free_pages_nolock()

[Yosry Ahmed <yosryahmed@google.com>]

On Tue, Dec 17, 2024 at 10:37 PM Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
>
> On Tue, Dec 17, 2024 at 9:58 PM Yosry Ahmed <yosryahmed@google.com> wrote:
> >
> > What I mean is, functions like __free_unref_page() and
> > free_unref_page_commit() now accept fpi_flags, but any flags other
> > than FPI_TRYLOCK are essentially ignored, also not very clear.
>
> They're not ignored. They are just not useful in this context.

I think they are. For example, if you pass FPI_SKIP_REPORT_NOTIFY to
__free_unref_page(), page_reporting_notify_free() will still be called
when the page is eventually freed to the buddy allocator. Same goes
for FPI_NO_TAIL.

> The code rules over comment. If you have a concrete suggestion on
> how to improve the comment please say so.

What I had in mind is adding a WARN in the pcp freeing functions if
any FPI flag but FPI_TRYLOCK is passed, and/or explicitly calling out
that other flags should not be passed as they have no effect in this
context (whether at the function definition, above the WARN, or at the
flag definitions).