linux-kernel - Re: [PATCH v3 bpf RESEND 3/4] module: introduce module_alloc

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Date:   Fri, 15 Apr 2022 12:03:42 -0700
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     Song Liu <song@...nel.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        bpf <bpf@...r.kernel.org>, Linux-MM <linux-mm@...ck.org>,
        open list <linux-kernel@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Kernel Team <kernel-team@...com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>,
        Christoph Hellwig <hch@...radead.org>, imbrenda@...ux.ibm.com
Subject: Re: [PATCH v3 bpf RESEND 3/4] module: introduce module_alloc_huge

On Thu, Apr 14, 2022 at 02:31:18PM -0700, Song Liu wrote:
> On Thu, Apr 14, 2022 at 2:11 PM Luis Chamberlain <mcgrof@...nel.org> wrote:
> >
> > On Thu, Apr 14, 2022 at 02:03:17PM -0700, Song Liu wrote:
> > > Hi Luis,
> > >
> > > On Thu, Apr 14, 2022 at 1:34 PM Luis Chamberlain <mcgrof@...nel.org> wrote:
> > > >
> > > > On Thu, Apr 14, 2022 at 12:59:13PM -0700, Song Liu wrote:
> > > > > Introduce module_alloc_huge, which allocates huge page backed memory in
> > > > > module memory space. The primary user of this memory is bpf_prog_pack
> > > > > (multiple BPF programs sharing a huge page).
> > > > >
> > > > > Signed-off-by: Song Liu <song@...nel.org>
> > > >
> > > > See modules-next [0], as modules.c has been chopped up as of late.
> > > > So if you want this to go throug modules this will need to rebased
> > > > on that tree. fortunately the amount of code in question does not
> > > > seem like much.
> > > >
> > > > [0] https://git.kernel.org/pub/scm/linux/kernel/git/mcgrof/linux.git/log/?h=modules-next
> > >
> > > We are hoping to ship this with to 5.18, as the set addresses some issue with
> > > huge page backed vmalloc. I guess we cannot ship it via modules-next branch.
> > >
> >
> > Huh, you intend this to go in as a fix for v5.18 (already released) once
> > properly reviewed?  This seems quite large... for a fix.
> >
> > > How about we ship module_alloc_huge() to 5.18 in module.c for now, and once
> > > we update modules-next branch, I will send another patch to clean it up?
> >
> > I rather set the expectations right about getting such a large fix in
> > for v5.18. I haven't even sat down to review all the changes in light of
> > this, but a cursorary glance seems to me it's rather "large" for a fix.
> 
> Yes, I agree this is a little too big for a fix. I guess we can discuss whether
> some of the set need to wait until 5.19.

Doing a more thorough review of this now, and when the other changes
landed, it seems this is *large follow up fix* for an optimization for when tons
of JIT eBPF programs are used. It's so large I can't be confident this also
doesn't go in with other holes or issues, or that the other stuff merged
already also has some other issues. So I can't see anything screaming
for why this needs to go in for v5.18 other than it'd be nice.

So my preference is for this to go through v5.19 as I see no rush.

  Luis