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From:   Marco Elver <elver@google.com>
Date:   Mon, 11 Jul 2022 18:26:27 +0200
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Subject: Re: [PATCH v4 10/45] libnvdimm/pfn_dev: increase MAX_STRUCT_PAGE_SIZE
To:     Alexander Potapenko <glider@google.com>
Cc:     Alexander Viro <viro@zeniv.linux.org.uk>,
        Alexei Starovoitov <ast@kernel.org>,
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On Fri, 1 Jul 2022 at 16:23, Alexander Potapenko <glider@google.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.


> Signed-off-by: Alexander Potapenko <glider@google.com>

Reviewed-by: Marco Elver <elver@google.com>

> ---
> Link: https://linux-review.googlesource.com/id/I353796acc6a850bfd7bb342aa1b63e616fc614f1
> ---
>  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 that
>                  * we don't have a dynamic reserve space depending on
>                  * struct page size. But we also want to make sure we notice
> --
> 2.37.0.rc0.161.g10f37bed90-goog
>