On Fri, May 22, 2020 at 09:33:35AM -0400, Qian Cai wrote:
> On Wed, May 20, 2020 at 07:25:20PM -0400, Johannes Weiner wrote:
> > Operations like MADV_FREE, FADV_DONTNEED etc. currently move any
> > affected active pages to the inactive list to accelerate their reclaim
> > (good) but also steer page reclaim toward that LRU type, or away from
> > the other (bad).
> >
> > The reason why this is undesirable is that such operations are not
> > part of the regular page aging cycle, and rather a fluke that doesn't
> > say much about the remaining pages on that list; they might all be in
> > heavy use, and once the chunk of easy victims has been purged, the VM
> > continues to apply elevated pressure on those remaining hot pages. The
> > other LRU, meanwhile, might have easily reclaimable pages, and there
> > was never a need to steer away from it in the first place.
> >
> > As the previous patch outlined, we should focus on recording actually
> > observed cost to steer the balance rather than speculating about the
> > potential value of one LRU list over the other. In that spirit, leave
> > explicitely deactivated pages to the LRU algorithm to pick up, and let
> > rotations decide which list is the easiest to reclaim.
> >
> > Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
> > Acked-by: Minchan Kim <minchan@xxxxxxxxxx>
> > Acked-by: Michal Hocko <mhocko@xxxxxxxx>
> > ---
> > mm/swap.c | 4 ----
> > 1 file changed, 4 deletions(-)
> >
> > diff --git a/mm/swap.c b/mm/swap.c
> > index 5d62c5a0c651..d7912bfb597f 100644
> > --- a/mm/swap.c
> > +++ b/mm/swap.c
> > @@ -515,14 +515,12 @@ static void lru_deactivate_file_fn(struct page *page, struct lruvec *lruvec,
> >
> > if (active)
> > __count_vm_event(PGDEACTIVATE);
> > - lru_note_cost(lruvec, !file, hpage_nr_pages(page));
> > }
> >
> []
>
> mm/swap.c: In function 'lru_deactivate_file_fn':
> mm/swap.c:504:11: warning: variable 'file' set but not used
> [-Wunused-but-set-variable]
> int lru, file;
> ^~~~
Oops, my gcc doesn't warn about that, but yes, it's clearly dead code.
$ make mm/swap.o
GEN Makefile
CALL /home/hannes/src/linux/linux/scripts/checksyscalls.sh
CALL /home/hannes/src/linux/linux/scripts/atomic/check-atomics.sh
DESCEND objtool
CC mm/swap.o
$
> This?
>
> diff --git a/mm/swap.c b/mm/swap.c
> index fedf5847dfdb..9c38c1b545af 100644
> --- a/mm/swap.c
> +++ b/mm/swap.c
> @@ -501,7 +501,7 @@ void lru_cache_add_active_or_unevictable(struct page *page,
> static void lru_deactivate_file_fn(struct page *page, struct lruvec *lruvec,
> void *arg)
> {
> - int lru, file;
> + int lru;
> bool active;
>
> if (!PageLRU(page))
> @@ -515,7 +515,6 @@ static void lru_deactivate_file_fn(struct page *page, struct lruvec *lruvec,
> return;
>
> active = PageActive(page);
> - file = page_is_file_lru(page);
> lru = page_lru_base_type(page);
>
> del_page_from_lru_list(page, lruvec, lru + active);
Looks good, and it appears Andrew has already queued it. Would you
mind providing the Signed-off-by: for it?
