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Date: Wed, 2 Aug 2023 12:32:35 +0200
From: AngeloGioacchino Del Regno
<angelogioacchino.delregno@...labora.com>
To: Kalesh Singh <kaleshsingh@...gle.com>, yuzhao@...gle.com,
akpm@...ux-foundation.org
Cc: surenb@...gle.com, android-mm@...gle.com, kernel-team@...roid.com,
stable@...r.kernel.org,
Charan Teja Kalla <quic_charante@...cinc.com>,
Lecopzer Chen <lecopzer.chen@...iatek.com>,
Matthias Brugger <matthias.bgg@...il.com>,
Suleiman Souhlal <suleiman@...gle.com>,
Oleksandr Natalenko <oleksandr@...alenko.name>,
"Jan Alexander Steffens (heftig)" <heftig@...hlinux.org>,
Qi Zheng <zhengqi.arch@...edance.com>,
Steven Barrett <steven@...uorix.net>,
Brian Geffon <bgeffon@...gle.com>,
Barry Song <baohua@...nel.org>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH v2 1/3] mm-unstable: Multi-gen LRU: Fix per-zone reclaim
Il 02/08/23 04:56, Kalesh Singh ha scritto:
> 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
>
> Fixes: ac35a4902374 ("mm: multi-gen LRU: minimal implementation")
> Cc: stable@...r.kernel.org
> Cc: Yu Zhao <yuzhao@...gle.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Reported-by: Charan Teja Kalla <quic_charante@...cinc.com>
> Reported-by: Lecopzer Chen <lecopzer.chen@...iatek.com>
> Signed-off-by: Kalesh Singh <kaleshsingh@...gle.com>
Whole series tested on MT8173 Elm Chromebook and MT6795 Xperia M5 as those are
low ram devices. Can't reproduce the issue described in your [1] link from RPi.
MediaTek:
Tested-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
> ---
>
> Changes in v2:
> - Add Fixes tag and cc stable
>
> mm/vmscan.c | 18 ++++++++++++++----
> 1 file changed, 14 insertions(+), 4 deletions(-)
>
> 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);
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