| Message ID | 20200520232525.798933-10-hannes@cmpxchg.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | mm: balance LRU lists based on relative thrashing v2 | expand |
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@cmpxchg.org> > Acked-by: Minchan Kim <minchan@kernel.org> > Acked-by: Michal Hocko <mhocko@suse.com> > --- > 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; ^~~~ 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);
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@cmpxchg.org> > > Acked-by: Minchan Kim <minchan@kernel.org> > > Acked-by: Michal Hocko <mhocko@suse.com> > > --- > > 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?
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)); } static void lru_deactivate_fn(struct page *page, struct lruvec *lruvec, void *arg) { if (PageLRU(page) && PageActive(page) && !PageUnevictable(page)) { - int file = page_is_file_lru(page); int lru = page_lru_base_type(page); del_page_from_lru_list(page, lruvec, lru + LRU_ACTIVE); @@ -531,7 +529,6 @@ static void lru_deactivate_fn(struct page *page, struct lruvec *lruvec, add_page_to_lru_list(page, lruvec, lru); __count_vm_events(PGDEACTIVATE, hpage_nr_pages(page)); - lru_note_cost(lruvec, !file, hpage_nr_pages(page)); } } @@ -556,7 +553,6 @@ static void lru_lazyfree_fn(struct page *page, struct lruvec *lruvec, __count_vm_events(PGLAZYFREE, hpage_nr_pages(page)); count_memcg_page_event(page, PGLAZYFREE); - lru_note_cost(lruvec, 0, hpage_nr_pages(page)); } }