diff mbox series

[1/3] mm-unstable: Multi-gen LRU: Fix per-zone reclaim

Message ID 20230802001938.3913174-1-kaleshsingh@google.com
State New
Headers
Series [1/3] mm-unstable: Multi-gen LRU: Fix per-zone reclaim |

Commit Message

Kalesh Singh Aug. 2, 2023, 12:19 a.m. UTC 
  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

Cc: Yu Zhao <yuzhao@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Reported-by: Charan Teja Kalla <quic_charante@quicinc.com>
Reported-by: Lecopzer Chen <lecopzer.chen@mediatek.com>
Signed-off-by: Kalesh Singh <kaleshsingh@google.com>
---
 mm/vmscan.c | 18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

Comments

Yu Zhao Aug. 2, 2023, 2:07 a.m. UTC | #1 
On Tue, Aug 1, 2023 at 6:19 PM Kalesh Singh <kaleshsingh@google.com> wrote:
>
> 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
>
> Cc: Yu Zhao <yuzhao@google.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Reported-by: Charan Teja Kalla <quic_charante@quicinc.com>
> Reported-by: Lecopzer Chen <lecopzer.chen@mediatek.com>
> Signed-off-by: Kalesh Singh <kaleshsingh@google.com>

LGTM. But I think we need the Fixes tag and Cc stable.
Kalesh Singh Aug. 2, 2023, 3 a.m. UTC | #2 
On Tue, Aug 1, 2023 at 7:08 PM Yu Zhao <yuzhao@google.com> wrote:
>
> On Tue, Aug 1, 2023 at 6:19 PM Kalesh Singh <kaleshsingh@google.com> wrote:
> >
> > 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
> >
> > Cc: Yu Zhao <yuzhao@google.com>
> > Cc: Andrew Morton <akpm@linux-foundation.org>
> > Reported-by: Charan Teja Kalla <quic_charante@quicinc.com>
> > Reported-by: Lecopzer Chen <lecopzer.chen@mediatek.com>
> > Signed-off-by: Kalesh Singh <kaleshsingh@google.com>
>
> LGTM. But I think we need the Fixes tag and Cc stable.

I've reposted the patches with fixes tag and stable cc'ed at:
https://lore.kernel.org/lkml/20230802025606.346758-1-kaleshsingh@google.com/#t

Thanks,
Kalesh
diff mbox series

Patch

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 4039620d30fe..489a4fc7d9b1 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -4889,7 +4889,8 @@  static int lru_gen_memcg_seg(struct lruvec *lruvec)
  *                          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);
@@ -4939,6 +4940,13 @@  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->folios[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))) {
@@ -4987,7 +4995,8 @@  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;
@@ -5003,9 +5012,10 @@  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->folios[gen][type][zone];
 
 		while (!list_empty(head)) {
@@ -5019,7 +5029,7 @@  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);