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From:   Alexander Potapenko <glider@google.com>
Date:   Wed, 3 Aug 2022 11:44:18 +0200
Message-ID: <CAG_fn=W2EUjS8AX1Odunq1==dV178s_-w3hQpyrFBr=Auo-Q-A@mail.gmail.com>
Subject: Re: [PATCH v4 10/45] libnvdimm/pfn_dev: increase MAX_STRUCT_PAGE_SIZE
To:     Marco Elver <elver@google.com>,
        Dan Williams <dan.j.williams@intel.com>
Cc:     Alexander Viro <viro@zeniv.linux.org.uk>,
        Alexei Starovoitov <ast@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Andrey Konovalov <andreyknvl@google.com>,
        Andy Lutomirski <luto@kernel.org>,
        Arnd Bergmann <arnd@arndb.de>, Borislav Petkov <bp@alien8.de>,
        Christoph Hellwig <hch@lst.de>,
        Christoph Lameter <cl@linux.com>,
        David Rientjes <rientjes@google.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Eric Dumazet <edumazet@google.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        Ilya Leoshkevich <iii@linux.ibm.com>,
        Ingo Molnar <mingo@redhat.com>, Jens Axboe <axboe@kernel.dk>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Kees Cook <keescook@chromium.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Matthew Wilcox <willy@infradead.org>,
        "Michael S. Tsirkin" <mst@redhat.com>,
        Pekka Enberg <penberg@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Petr Mladek <pmladek@suse.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Vasily Gorbik <gor@linux.ibm.com>,
        Vegard Nossum <vegard.nossum@oracle.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        kasan-dev <kasan-dev@googlegroups.com>,
        Linux Memory Management List <linux-mm@kvack.org>,
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(+ Dan Williams)
(resending with patch context included)

On Mon, Jul 11, 2022 at 6:27 PM Marco Elver <elver@google.com> wrote:
>
> On Fri, 1 Jul 2022 at 16:23, Alexander Potapenko <glider@google.com> wrot=
e:
> >
> > KMSAN adds extra metadata fields to struct page, so it does not fit int=
o
> > 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 loade=
d.
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@google.com>
>
> Reviewed-by: Marco Elver <elver@google.com>
>
> > ---
> > Link: https://linux-review.googlesource.com/id/I353796acc6a850bfd7bb342=
aa1b63e616fc614f1
> > ---
> >  drivers/nvdimm/nd.h       | 2 +-
> >  drivers/nvdimm/pfn_devs.c | 2 +-
> >  2 files changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/nvdimm/nd.h b/drivers/nvdimm/nd.h
> > index ec5219680092d..85ca5b4da3cf3 100644
> > --- a/drivers/nvdimm/nd.h
> > +++ b/drivers/nvdimm/nd.h
> > @@ -652,7 +652,7 @@ void devm_namespace_disable(struct device *dev,
> >                 struct nd_namespace_common *ndns);
> >  #if IS_ENABLED(CONFIG_ND_CLAIM)
> >  /* max struct page size independent of kernel config */
> > -#define MAX_STRUCT_PAGE_SIZE 64
> > +#define MAX_STRUCT_PAGE_SIZE 128
> >  int nvdimm_setup_pfn(struct nd_pfn *nd_pfn, struct dev_pagemap *pgmap)=
;
> >  #else
> >  static inline int nvdimm_setup_pfn(struct nd_pfn *nd_pfn,
> > diff --git a/drivers/nvdimm/pfn_devs.c b/drivers/nvdimm/pfn_devs.c
> > index 0e92ab4b32833..61af072ac98f9 100644
> > --- a/drivers/nvdimm/pfn_devs.c
> > +++ b/drivers/nvdimm/pfn_devs.c
> > @@ -787,7 +787,7 @@ static int nd_pfn_init(struct nd_pfn *nd_pfn)
> >                  * when populating the vmemmap. This *should* be equal =
to
> >                  * PMD_SIZE for most architectures.
> >                  *
> > -                * Also make sure size of struct page is less than 64. =
We
> > +                * Also make sure size of struct page is less than 128.=
 We
> >                  * want to make sure we use large enough size here so t=
hat
> >                  * we don't have a dynamic reserve space depending on
> >                  * struct page size. But we also want to make sure we n=
otice
> > --
> > 2.37.0.rc0.161.g10f37bed90-goog
> >


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Alexander Potapenko
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