MGLRU has a LRU list for each zone for each type (anon/file) in each generation:
long nr_pages[MAX_NR_GENS][ANON_AND_FILE][MAX_NR_ZONES];
The min_seq (oldest generation) can progress independently for each type but the max_seq (youngest generation) is shared for both anon and file. This is to maintain a common frame of reference.
In order for eviction to advance the min_seq of a type, all the per-zone lists in the oldest generation of that type must be empty.
The eviction logic only considers pages from eligible zones for eviction or promotion.
scan_folios() { ... for (zone = sc->reclaim_idx; zone >= 0; zone--) { ... sort_folio(); // Promote ... isolate_folio(); // Evict } ... }
Consider the system has the movable zone configured and default 4 generations. The current state of the system is as shown below (only illustrating one type for simplicity):
Type: ANON
Zone DMA32 Normal Movable Device
Gen 0 0 0 4GB 0
Gen 1 0 1GB 1MB 0
Gen 2 1MB 4GB 1MB 0
Gen 3 1MB 1MB 1MB 0
Now consider there is a GFP_KERNEL allocation request (eligible zone index <= Normal), evict_folios() will return without doing any work since there are no pages to scan in the eligible zones of the oldest generation. Reclaim won't make progress until triggered from a ZONE_MOVABLE allocation request; which may not happen soon if there is a lot of free memory in the movable zone. This can lead to OOM kills, although there is 1GB pages in the Normal zone of Gen 1 that we have not yet tried to reclaim.
This issue is not seen in the conventional active/inactive LRU since there are no per-zone lists.
If there are no (not enough) folios to scan in the eligible zones, move folios from ineligible zone (zone_index > reclaim_index) to the next generation. This allows for the progression of min_seq and reclaiming from the next generation (Gen 1).
Qualcomm, Mediatek and raspberrypi [1] discovered this issue independently.
[1] https://github.com/raspberrypi/linux/issues/5395
Link: https://lkml.kernel.org/r/20230802025606.346758-1-kaleshsingh@google.com Fixes: ac35a4902374 ("mm: multi-gen LRU: minimal implementation") Signed-off-by: Kalesh Singh kaleshsingh@google.com Reported-by: Charan Teja Kalla quic_charante@quicinc.com Reported-by: Lecopzer Chen lecopzer.chen@mediatek.com Tested-by: AngeloGioacchino Del Regno angelogioacchino.delregno@collabora.com [mediatek] Tested-by: Charan Teja Kalla quic_charante@quicinc.com Cc: Yu Zhao yuzhao@google.com Cc: Barry Song baohua@kernel.org Cc: Brian Geffon bgeffon@google.com Cc: Jan Alexander Steffens (heftig) heftig@archlinux.org Cc: Matthias Brugger matthias.bgg@gmail.com Cc: Oleksandr Natalenko oleksandr@natalenko.name Cc: Qi Zheng zhengqi.arch@bytedance.com Cc: Steven Barrett steven@liquorix.net Cc: Suleiman Souhlal suleiman@google.com Cc: Suren Baghdasaryan surenb@google.com Cc: Aneesh Kumar K V aneesh.kumar@linux.ibm.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org (cherry picked from commit 669281ee7ef731fb5204df9d948669bf32a5e68d) [ Kalesh Singh - Fix conflicts caused by rename of lrugen->lists to lrugen->folios ] Signed-off-by: Kalesh Singh kaleshsingh@google.com --- mm/vmscan.c | 18 ++++++++++++++---- 1 file changed, 14 insertions(+), 4 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c index d18296109aa7..d7016fdb7c14 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -4728,7 +4728,8 @@ void lru_gen_look_around(struct page_vma_mapped_walk *pvmw) * the eviction ******************************************************************************/
-static bool sort_folio(struct lruvec *lruvec, struct folio *folio, int tier_idx) +static bool sort_folio(struct lruvec *lruvec, struct folio *folio, struct scan_control *sc, + int tier_idx) { bool success; int gen = folio_lru_gen(folio); @@ -4779,6 +4780,13 @@ static bool sort_folio(struct lruvec *lruvec, struct folio *folio, int tier_idx) return true; }
+ /* ineligible */ + if (zone > sc->reclaim_idx) { + gen = folio_inc_gen(lruvec, folio, false); + list_move_tail(&folio->lru, &lrugen->lists[gen][type][zone]); + return true; + } + /* waiting for writeback */ if (folio_test_locked(folio) || folio_test_writeback(folio) || (type == LRU_GEN_FILE && folio_test_dirty(folio))) { @@ -4831,7 +4839,8 @@ static bool isolate_folio(struct lruvec *lruvec, struct folio *folio, struct sca static int scan_folios(struct lruvec *lruvec, struct scan_control *sc, int type, int tier, struct list_head *list) { - int gen, zone; + int i; + int gen; enum vm_event_item item; int sorted = 0; int scanned = 0; @@ -4847,9 +4856,10 @@ static int scan_folios(struct lruvec *lruvec, struct scan_control *sc,
gen = lru_gen_from_seq(lrugen->min_seq[type]);
- for (zone = sc->reclaim_idx; zone >= 0; zone--) { + for (i = MAX_NR_ZONES; i > 0; i--) { LIST_HEAD(moved); int skipped = 0; + int zone = (sc->reclaim_idx + i) % MAX_NR_ZONES; struct list_head *head = &lrugen->lists[gen][type][zone];
while (!list_empty(head)) { @@ -4863,7 +4873,7 @@ static int scan_folios(struct lruvec *lruvec, struct scan_control *sc,
scanned += delta;
- if (sort_folio(lruvec, folio, tier)) + if (sort_folio(lruvec, folio, sc, tier)) sorted += delta; else if (isolate_folio(lruvec, folio, sc)) { list_add(&folio->lru, list);