On Fri, Feb 10, 2017 at 02:02:36PM +0100, Michal Hocko wrote:

On Fri 03-02-17 15:33:18, Shaohua Li wrote:

quoted

Userspace indicates MADV_FREE pages could be freed without pageout, so
it pretty much likes used once file pages. For such pages, we'd like to
reclaim them once there is memory pressure. Also it might be unfair
reclaiming MADV_FREE pages always before used once file pages and we
definitively want to reclaim the pages before other anonymous and file
pages.

To speed up MADV_FREE pages reclaim, we put the pages into
LRU_INACTIVE_FILE list. The rationale is LRU_INACTIVE_FILE list is tiny
nowadays and should be full of used once file pages. Reclaiming
MADV_FREE pages will not have much interfere of anonymous and active
file pages. And the inactive file pages and MADV_FREE pages will be
reclaimed according to their age, so we don't reclaim too many MADV_FREE
pages too. Putting the MADV_FREE pages into LRU_INACTIVE_FILE_LIST also
means we can reclaim the pages without swap support. This idea is
suggested by Johannes.

We also clear the pages SwapBacked flag to indicate they are MADV_FREE
pages.

I like this. I have expected this to be more convoluted but it looks
quite straightforward. I didn't get to do a really deep review and add
my acked-by but from a quick look there do not seem to be any surprises.
I was worried about vmstat accounting. There are some places which
isolate page from LRU and account based on the LRU and later use
page_is_file_cache to tell which LRU this was. This should work fine,
though, because you never touch pages which are off-lru.

That being said I do not see any major issues. There might be some minor
things and this will need a lot of testing but it is definitely a move
into right direction. I hope to do the deeper review after I get back
from vacation (20th Feb).

Sweat! Thanks for your time! 

quoted

Cc: Michal Hocko <mhocko@suse.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Rik van Riel <redacted>
Cc: Mel Gorman <redacted>
Cc: Andrew Morton <akpm@linux-foundation.org>

I guess
Suggested-by: Johannes Weiner <hannes@cmpxchg.org>

would be appropriate.

Sure, will add in next post and will add 'the patches are based on Minchan's
patches' too.

Thanks,
Shaohua

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