On Fri, Apr 21, 2017 at 12:12 AM, Oliver O'Halloran <ooh...@gmail.com> wrote:
> Read the default alignment from the hpage_pmd_size in sysfs. On PPC the
> PMD size depends on the MMU being used. When the traditional hash MMU is
> used (P9 and earlier) the PMD size is 16MB while the newer radix MMU
> uses a 2MB PMD size. The choice of MMU is done at runtime depending on
> what the hardware supports so we need to detect this at runtime rather
> than hardcoding it.
>
> Signed-off-by: Oliver O'Halloran <ooh...@gmail.com>
> ---
> ndctl/Makefile.am | 3 ++-
> ndctl/builtin-xaction-namespace.c | 41
> +++++++++++++++++++++++++++++----------
> 2 files changed, 33 insertions(+), 11 deletions(-)
>
> diff --git a/ndctl/Makefile.am b/ndctl/Makefile.am
> index c563e9411cc3..6d565c643efd 100644
> --- a/ndctl/Makefile.am
> +++ b/ndctl/Makefile.am
> @@ -10,7 +10,8 @@ ndctl_SOURCES = ndctl.c \
> ../util/log.c \
> builtin-list.c \
> builtin-test.c \
> - ../util/json.c
> + ../util/json.c \
> + ../util/sysfs.c
>
> if ENABLE_SMART
> ndctl_SOURCES += util/json-smart.c
> diff --git a/ndctl/builtin-xaction-namespace.c
> b/ndctl/builtin-xaction-namespace.c
> index d6c38dc15984..713a95987d91 100644
> --- a/ndctl/builtin-xaction-namespace.c
> +++ b/ndctl/builtin-xaction-namespace.c
> @@ -22,6 +22,7 @@
> #include <sys/types.h>
> #include <util/size.h>
> #include <util/json.h>
> +#include <util/sysfs.h>
> #include <json-c/json.h>
> #include <util/filter.h>
> #include <ndctl/libndctl.h>
> @@ -54,6 +55,8 @@ static struct parameters {
> const char *align;
> } param;
>
> +char default_align_buf[SYSFS_ATTR_SIZE];
> +
> void builtin_xaction_namespace_reset(void)
> {
> /*
> @@ -137,7 +140,24 @@ enum namespace_action {
> ACTION_DESTROY,
> };
>
> -static int set_defaults(enum namespace_action mode)
> +const char *sysfs_read_default_align(struct ndctl_ctx *ctx, const char *def,
> + const char *path)
> +{
> + /*
> + * HACK: The command handlers aren't supposed to write into
> + * the ndctl command context, but we want the debug
> + * output to go somewhere sensible.
> + */
> + if (__sysfs_read_attr((struct log_ctx *)ctx, path, default_align_buf))
> + return strdup(def);
> +
> + if (!strlen(default_align_buf))
> + return def;
> +
> + return default_align_buf;
I chatted with Dave Hansen about this and we're thinking we should go
ahead and add a new attribute to the device-dax sysfs with the list of
supported alignments, similar to what we have in the btt case for
supported sector sizes.
The reason is that the sensitivity to page sizes is a device-dax
internal requirement. Theoretically device-dax could support any
alignment and handle it with a mix of page sizes. However, since
device-dax wants to be strict and predictable about the tlb size
backing a given device-dax mapping then it should list the possible
options.
Looking at the transparent_hugepage sysfs is a bit of a layering
violation. There is no strict guarantee that device-dax is tied to thp
in the longterm. The thp sysfs is also awkward because it does not
tell us the pud page size.
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