mm/vmscan: more restrictive condition for retry in do_try_to_free_pages

By reviewing code, I find that when enter do_try_to_free_pages, the
may_thrash is always clear, and it will retry shrink zones to tap
cgroup's reserves memory by setting may_thrash when the former
shrink_zones reclaim nothing.

However, when memcg is disabled or on legacy hierarchy, or there do not
have any memcg protected by low limit, it should not do this useless
retry at all, for we do not have any cgroup's reserves memory to tap,
and we have already done hard work but made no progress, which as Michal
pointed out in former version, we are trying hard to control the retry
logical of page alloctor, and the current additional round of reclaim is
just lame.

Therefore, to avoid this unneeded retrying and make code more readable,
we remove the may_thrash field in scan_control, instead, introduce
memcg_low_reclaim and memcg_low_skipped, and only retry when
memcg_low_skipped, by setting memcg_low_reclaim.

[[email protected]: remove may_thrash field, introduce mem_cgroup_reclaim]
  Link: http://lkml.kernel.org/r/[email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Yisheng Xie <[email protected]>
Acked-by: Michal Hocko <[email protected]>
Suggested-by: Johannes Weiner <[email protected]>
Suggested-by: Michal Hocko <[email protected]>
Suggested-by: Shakeel Butt <[email protected]>
Reviewed-by: Shakeel Butt <[email protected]>
Acked-by: Johannes Weiner <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: Rik van Riel <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

0 files changed, 0 insertions, 0 deletions