linux-kernel - Re: [PATCH v4 10/45] libnvdimm/pfn_dev: increase MAX_STRUCT_PAGE

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Date:   Wed, 3 Aug 2022 11:41:46 +0200
From:   Alexander Potapenko <glider@...gle.com>
To:     Marco Elver <elver@...gle.com>,
        Dan Williams <dan.j.williams@...el.com>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Alexei Starovoitov <ast@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Arnd Bergmann <arnd@...db.de>, Borislav Petkov <bp@...en8.de>,
        Christoph Hellwig <hch@....de>,
        Christoph Lameter <cl@...ux.com>,
        David Rientjes <rientjes@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Ilya Leoshkevich <iii@...ux.ibm.com>,
        Ingo Molnar <mingo@...hat.com>, Jens Axboe <axboe@...nel.dk>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Kees Cook <keescook@...omium.org>,
        Mark Rutland <mark.rutland@....com>,
        Matthew Wilcox <willy@...radead.org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Pekka Enberg <penberg@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Vegard Nossum <vegard.nossum@...cle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        kasan-dev <kasan-dev@...glegroups.com>,
        Linux Memory Management List <linux-mm@...ck.org>,
        Linux-Arch <linux-arch@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 10/45] libnvdimm/pfn_dev: increase MAX_STRUCT_PAGE_SIZE

(+ Dan Williams)

On Mon, Jul 11, 2022 at 6:27 PM Marco Elver <elver@...gle.com> wrote:
>
> On Fri, 1 Jul 2022 at 16:23, Alexander Potapenko <glider@...gle.com> wrote:
> >
> > KMSAN adds extra metadata fields to struct page, so it does not fit into
> > 64 bytes anymore.
>
> Does this somehow cause extra space being used in all kernel configs?
> If not, it would be good to note this in the commit message.

I actually couldn't verify this on QEMU, because the driver never got loaded.
Looks like this increases the amount of memory used by the nvdimm
driver in all kernel configs that enable it (including those that
don't use KMSAN), but I am not sure how much is that.

Dan, do you know how bad increasing MAX_STRUCT_PAGE_SIZE can be?

>
> > Signed-off-by: Alexander Potapenko <glider@...gle.com>
>
> Reviewed-by: Marco Elver <elver@...gle.com>