On Wed, Jul 27, 2016 at 04:13:33PM +0100, Mel Gorman wrote: > On Wed, Jul 27, 2016 at 03:22:26PM +0100, Mel Gorman wrote: > > ---8<--- > > From: Mel Gorman <[email protected]> > > Subject: [PATCH] mm, vmscan: Wait on a waitqueue when too many pages are > > isolated > > > > This is potentially a much better version as it avoids wakeup storms and > do a better job of handling the case where pages could not be reclaimed. > > ---8<--- > mm, vmscan: Wait on a waitqueue when too many pages are isolated > > When too many pages are isolated, direct reclaim waits on congestion to > clear for up to a tenth of a second. There is no reason to believe that too > many pages are isolated due to dirty pages, reclaim efficiency or congestion. > It may simply be because an extremely large number of processes have entered > direct reclaim at the same time. > > This patch has processes wait on a waitqueue when too many pages are > isolated. When parallel reclaimers finish shrink_page_list, they wake the > waiters to recheck whether too many pages are isolated. While it is difficult > to trigger this corner case, it's possible by lauching an extremely large > number of hackbench processes on a 32-bit system with limited memory. Without > the patch, a large number of processes wait uselessly and with the patch > applied, I was unable to stall the system. > > Signed-off-by: Mel Gorman <[email protected]> > --- > include/linux/mmzone.h | 1 + > mm/page_alloc.c | 1 + > mm/vmscan.c | 24 +++++++++++++++--------- > 3 files changed, 17 insertions(+), 9 deletions(-) > > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h > index d572b78b65e1..467878d7af33 100644 > --- a/include/linux/mmzone.h > +++ b/include/linux/mmzone.h > @@ -653,6 +653,7 @@ typedef struct pglist_data { > int node_id; > wait_queue_head_t kswapd_wait; > wait_queue_head_t pfmemalloc_wait; > + wait_queue_head_t isolated_wait; > struct task_struct *kswapd; /* Protected by > mem_hotplug_begin/end() */ > int kswapd_order; > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index fbd329e61bf6..3800972f240e 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -5859,6 +5859,7 @@ static void __paginginit free_area_init_core(struct > pglist_data *pgdat) > #endif > init_waitqueue_head(&pgdat->kswapd_wait); > init_waitqueue_head(&pgdat->pfmemalloc_wait); > + init_waitqueue_head(&pgdat->isolated_wait); > #ifdef CONFIG_COMPACTION > init_waitqueue_head(&pgdat->kcompactd_wait); > #endif > diff --git a/mm/vmscan.c b/mm/vmscan.c > index 9c0b2b0fc164..e264fcb7556b 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -1554,16 +1554,16 @@ int isolate_lru_page(struct page *page) > * the LRU list will go small and be scanned faster than necessary, leading > to > * unnecessary swapping, thrashing and OOM. > */ > -static int too_many_isolated(struct pglist_data *pgdat, int file, > +static bool safe_to_isolate(struct pglist_data *pgdat, int file, > struct scan_control *sc) > { > unsigned long inactive, isolated; > > if (current_is_kswapd()) > - return 0; > + return true; > > - if (!sane_reclaim(sc)) > - return 0; > + if (sane_reclaim(sc)) > + return true; > > if (file) { > inactive = node_page_state(pgdat, NR_INACTIVE_FILE); > @@ -1581,7 +1581,7 @@ static int too_many_isolated(struct pglist_data *pgdat, > int file, > if ((sc->gfp_mask & (__GFP_IO | __GFP_FS)) == (__GFP_IO | __GFP_FS)) > inactive >>= 3; > > - return isolated > inactive; > + return isolated < inactive; > } > > static noinline_for_stack void > @@ -1701,12 +1701,15 @@ shrink_inactive_list(unsigned long nr_to_scan, struct > lruvec *lruvec, > if (!inactive_reclaimable_pages(lruvec, sc, lru)) > return 0; > > - while (unlikely(too_many_isolated(pgdat, file, sc))) { > - congestion_wait(BLK_RW_ASYNC, HZ/10); > + if (!safe_to_isolate(pgdat, file, sc)) { > + wait_event_killable(pgdat->isolated_wait, > + safe_to_isolate(pgdat, file, sc)); > > /* We are about to die and free our memory. Return now. */ > - if (fatal_signal_pending(current)) > - return SWAP_CLUSTER_MAX; > + if (fatal_signal_pending(current)) { > + nr_reclaimed = SWAP_CLUSTER_MAX; > + goto out; > + } > } > > lru_add_drain(); > @@ -1819,6 +1822,9 @@ shrink_inactive_list(unsigned long nr_to_scan, struct > lruvec *lruvec, > trace_mm_vmscan_lru_shrink_inactive(pgdat->node_id, > nr_scanned, nr_reclaimed, > sc->priority, file); > + > +out: > + wake_up(&pgdat->isolated_wait);
Isolation can happen migrate/khugepaged as well as reclaim so it would sleep forever unless all of places can isolate pages don't wake up.
