Multi-gen LRU: fix per-zone reclaim

commit 669281ee7ef731fb5204df9d948669bf32a5e68d upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 0400e3b..78efee4 100644 (file)
--- 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->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))) {
@@ -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->folios[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);