linux-kernel - Re: [RFC PATCH 00/30] Code tagging framework and applications

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Message-ID: <20220908070719.ootyzzbd47dd5rkv@kmo-framework>
Date:   Thu, 8 Sep 2022 03:07:19 -0400
From:   Kent Overstreet <kent.overstreet@...ux.dev>
To:     Suren Baghdasaryan <surenb@...gle.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Michal Hocko <mhocko@...e.com>, Mel Gorman <mgorman@...e.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Johannes Weiner <hannes@...xchg.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Davidlohr Bueso <dave@...olabs.net>,
        Matthew Wilcox <willy@...radead.org>,
        "Liam R. Howlett" <liam.howlett@...cle.com>,
        David Vernet <void@...ifault.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Laurent Dufour <ldufour@...ux.ibm.com>,
        Peter Xu <peterx@...hat.com>,
        David Hildenbrand <david@...hat.com>,
        Jens Axboe <axboe@...nel.dk>, mcgrof@...nel.org,
        masahiroy@...nel.org, nathan@...nel.org, changbin.du@...el.com,
        ytcoode@...il.com, Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Benjamin Segall <bsegall@...gle.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Valentin Schneider <vschneid@...hat.com>,
        Christopher Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        Joonsoo Kim <iamjoonsoo.kim@....com>, 42.hyeyoo@...il.com,
        Alexander Potapenko <glider@...gle.com>,
        Marco Elver <elver@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Muchun Song <songmuchun@...edance.com>, arnd@...db.de,
        jbaron@...mai.com, David Rientjes <rientjes@...gle.com>,
        Minchan Kim <minchan@...gle.com>,
        Kalesh Singh <kaleshsingh@...gle.com>,
        kernel-team <kernel-team@...roid.com>,
        linux-mm <linux-mm@...ck.org>, iommu@...ts.linux.dev,
        kasan-dev@...glegroups.com, io-uring@...r.kernel.org,
        linux-arch@...r.kernel.org, xen-devel@...ts.xenproject.org,
        linux-bcache@...r.kernel.org, linux-modules@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 00/30] Code tagging framework and applications

On Wed, Sep 07, 2022 at 11:49:37PM -0700, Suren Baghdasaryan wrote:
> I would really appreciate if everyone could please stick to the
> technical side of the conversation. That way we can get some
> constructive feedback. Everything else is not helpful and at best is a
> distraction.
> Maintenance burden is a price we pay and I think it's the prerogative
> of the maintainers to take that into account. Our job is to prove that
> the price is worth paying.

Well said.

I'd also like to add - slab.h does look pretty overgrown and messy. We've grown
a _lot_ of special purpose memory allocation interfaces, and I think it probably
is time to try and wrangle that back.

The API complexity isn't just an issue for this patch - it's an issue for
anything that has to wrap and plumb through memory allocation interfaces. It's a
pain point for the Rust people, and also comes in e.g. the mempool API.

I think we should keep going with the memalloc_no*_save()/restore() approach,
and extend it to other things:

 - memalloc_nowait_save()
 - memalloc_highpri_save()

(these two get you GFP_ATOMIC).

Also, I don't think these all need to be separate functions, we could have

memalloc_gfp_apply()
memalloc_gfp_restore()

which simply takes a gfp flags argument and applies it to the current
PF_MEMALLOC flags.

We've had long standing bugs where vmalloc() can't correctly take gfp flags
because some of the allocations it does for page tables don't have it correctly
plumbed through; switching to the memalloc_*_(save|restore) is something people
have been wanting in order to fix this - for years. Actually following through
and completing this would let us kill the gfp flags arguments to our various
memory allocators entirely.

I think we can do the same thing with the numa node parameter - kill
kmalloc_node() et. all, move it to task_struct with a set of save/restore
functions.

There's probably other things we can do to simplify slab.h if we look more. I've
been hoping to start pushing patches for some of this stuff - it's going to be
some time before I can get to it though, can only handle so many projects in
flight at a time :)