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SubjectRe: [RFC 2/2] cma: support MIGRATE_DISCARD
Date
Minchan Kim <minchan@kernel.org> writes:
> This patch introudes MIGRATE_DISCARD mode in migration.
> It drop clean cache pages instead of migration so that
> migration latency could be reduced. Of course, it could
> evict code pages but latency of big contiguous memory
> is more important than some background application's slow down
> in mobile embedded enviroment.
>
> Signed-off-by: Minchan Kim <minchan@kernel.org>

This looks good to me.

> ---
> include/linux/migrate_mode.h | 11 +++++++---
> mm/migrate.c | 50 +++++++++++++++++++++++++++++++++---------
> mm/page_alloc.c | 2 +-
> 3 files changed, 49 insertions(+), 14 deletions(-)
>
> diff --git a/include/linux/migrate_mode.h b/include/linux/migrate_mode.h
> index ebf3d89..04ca19c 100644
> --- a/include/linux/migrate_mode.h
> +++ b/include/linux/migrate_mode.h
> @@ -6,11 +6,16 @@
> * on most operations but not ->writepage as the potential stall time
> * is too significant
> * MIGRATE_SYNC will block when migrating pages
> + * MIGRTATE_DISCARD will discard clean cache page instead of migration
> + *
> + * MIGRATE_ASYNC, MIGRATE_SYNC_LIGHT, MIGRATE_SYNC shouldn't be used
> + * together as OR flag.
> */
> enum migrate_mode {
> - MIGRATE_ASYNC,
> - MIGRATE_SYNC_LIGHT,
> - MIGRATE_SYNC,
> + MIGRATE_ASYNC = 1 << 0,
> + MIGRATE_SYNC_LIGHT = 1 << 1,
> + MIGRATE_SYNC = 1 << 2,
> + MIGRATE_DISCARD = 1 << 3,
> };

Since CMA is the only user of MIGRATE_DISCARD it may be worth it to
guard it inside an #ifdef, eg:

#ifdef CONFIG_CMA
MIGRATE_DISCARD = 1 << 3,
#define is_migrate_discard(mode) (((mode) & MIGRATE_DISCARD) == MIGRATE_DISCARD)
#endif


> #endif /* MIGRATE_MODE_H_INCLUDED */
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 77ed2d7..8119a59 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -685,9 +685,12 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
> int remap_swapcache = 1;
> struct mem_cgroup *mem;
> struct anon_vma *anon_vma = NULL;
> + enum ttu_flags ttu_flags;
> + bool discard_mode = false;
> + bool file = false;
>
> if (!trylock_page(page)) {
> - if (!force || mode == MIGRATE_ASYNC)
> + if (!force || mode & MIGRATE_ASYNC)

+ if (!force || (mode & MIGRATE_ASYNC))

> goto out;
>
> /*


--
Best regards, _ _
.o. | Liege of Serenely Enlightened Majesty of o' \,=./ `o
..o | Computer Science, Michał “mina86” Nazarewicz (o o)
ooo +----<email/xmpp: mpn@google.com>--------------ooO--(_)--Ooo--[unhandled content-type:application/pgp-signature]
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