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SubjectRe: [RFC v2 PATCH 2/8] mm: introduce MIGRATE_MIRROR to manage the mirrored pages
On 2015/06/27 11:24, Xishi Qiu wrote:
> This patch introduces a new migratetype called "MIGRATE_MIRROR", it is used to
> allocate mirrored pages.
> When cat /proc/pagetypeinfo, you can see the count of free mirrored blocks.
>
> Signed-off-by: Xishi Qiu <qiuxishi@huawei.com>

My fear about this approarch is that this may break something existing.

Now, when we add MIGRATE_MIRROR type, we'll hide attributes of pageblocks as
MIGRATE_UNMOVABOLE, MIGRATE_RECLAIMABLE, MIGRATE_MOVABLE.

Logically, MIRROR attribute is independent from page mobility and this overwrites
will make some information lost.

Then,

> ---
> include/linux/mmzone.h | 9 +++++++++
> mm/page_alloc.c | 3 +++
> mm/vmstat.c | 3 +++
> 3 files changed, 15 insertions(+)
>
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index 54d74f6..54e891a 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -39,6 +39,9 @@ enum {
> MIGRATE_UNMOVABLE,
> MIGRATE_RECLAIMABLE,
> MIGRATE_MOVABLE,
> +#ifdef CONFIG_MEMORY_MIRROR
> + MIGRATE_MIRROR,
> +#endif

I think
MIGRATE_MIRROR_UNMOVABLE,
MIGRATE_MIRROR_RECLAIMABLE,
MIGRATE_MIRROR_MOVABLE, <== adding this may need discuss.
MIGRATE_MIRROR_RESERVED, <== reserved pages should be maintained per mirrored/unmirrored.

should be added with the following fallback list.

/*
* MIRROR page range is defined by firmware at boot. The range is limited
* and is used only for kernel memory mirroring.
*/
[MIGRATE_UNMOVABLE_MIRROR] = {MIGRATE_RECLAIMABLE_MIRROR, MIGRATE_RESERVE}
[MIGRATE_RECLAIMABLE_MIRROR] = {MIGRATE_UNMOVABLE_MIRROR, MIGRATE_RESERVE}

Then, we'll not lose the original information of "Reclaiable Pages".

One problem here is whteher we should have MIGRATE_RESERVE_MIRROR.

If we never allow users to allocate mirrored memory, we should have MIGRATE_RESERVE_MIRROR.
But it seems to require much more code change to do that.

Creating a zone or adding an attribues to zones are another design choice.

Anyway, your patch doesn't takes care of reserved memory calculation at this point.
Please check setup_zone_migrate_reserve() That will be a problem.

Thanks,
-Kame

> MIGRATE_PCPTYPES, /* the number of types on the pcp lists */
> MIGRATE_RESERVE = MIGRATE_PCPTYPES,
> #ifdef CONFIG_CMA
> @@ -69,6 +72,12 @@ enum {
> # define is_migrate_cma(migratetype) false
> #endif
>
> +#ifdef CONFIG_MEMORY_MIRROR
> +# define is_migrate_mirror(migratetype) unlikely((migratetype) == MIGRATE_MIRROR)
> +#else
> +# define is_migrate_mirror(migratetype) false
> +#endif
> +
> #define for_each_migratetype_order(order, type) \
> for (order = 0; order < MAX_ORDER; order++) \
> for (type = 0; type < MIGRATE_TYPES; type++)
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index ebffa0e..6e4d79f 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -3216,6 +3216,9 @@ static void show_migration_types(unsigned char type)
> [MIGRATE_UNMOVABLE] = 'U',
> [MIGRATE_RECLAIMABLE] = 'E',
> [MIGRATE_MOVABLE] = 'M',
> +#ifdef CONFIG_MEMORY_MIRROR
> + [MIGRATE_MIRROR] = 'O',
> +#endif
> [MIGRATE_RESERVE] = 'R',
> #ifdef CONFIG_CMA
> [MIGRATE_CMA] = 'C',
> diff --git a/mm/vmstat.c b/mm/vmstat.c
> index 4f5cd97..d0323e0 100644
> --- a/mm/vmstat.c
> +++ b/mm/vmstat.c
> @@ -901,6 +901,9 @@ static char * const migratetype_names[MIGRATE_TYPES] = {
> "Unmovable",
> "Reclaimable",
> "Movable",
> +#ifdef CONFIG_MEMORY_MIRROR
> + "Mirror",
> +#endif
> "Reserve",
> #ifdef CONFIG_CMA
> "CMA",
>




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