Re: [RFC 01/13] mm, compaction: don't isolate PageWriteback pages in MIGRATE_SYNC_LIGHT mode

Michal Hocko
2016-05-11T12:40:44Z

On Tue 10-05-16 09:35:51, Vlastimil Babka wrote:
> From: Hugh Dickins <hughd@google.com>
>
> At present MIGRATE_SYNC_LIGHT is allowing __isolate_lru_page() to
> isolate a PageWriteback page, which __unmap_and_move() then rejects
> with -EBUSY: of course the writeback might complete in between, but
> that's not what we usually expect, so probably better not to isolate it.

this makes a lot of sense regardless the rest of the series. I will have
a look at the rest tomorrow more closely.

>
> Signed-off-by: Hugh Dickins <hughd@google.com>
> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>

Acked-by: Michal Hocko <mhocko@suse.com>

> ---
> mm/compaction.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/compaction.c b/mm/compaction.c
> index c72987603343..481004c73c90 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -1146,7 +1146,7 @@ static isolate_migrate_t isolate_migratepages(struct zone *zone,
> struct page *page;
> const isolate_mode_t isolate_mode =
> (sysctl_compact_unevictable_allowed ? ISOLATE_UNEVICTABLE : 0) |
> - (cc->mode == MIGRATE_ASYNC ? ISOLATE_ASYNC_MIGRATE : 0);
> + (cc->mode != MIGRATE_SYNC ? ISOLATE_ASYNC_MIGRATE : 0);
>
> /*
> * Start at where we last stopped, or beginning of the zone as
> --
> 2.8.2

--
Michal Hocko
SUSE Labs