| Message ID | 20230802025606.346758-1-kaleshsingh@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v2,1/3] mm-unstable: Multi-gen LRU: Fix per-zone reclaim | expand |
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@vger.kernel.org > 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> 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@collabora.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);
Thanks Kalesh for taking this to upstream. On 8/2/2023 8:26 AM, Kalesh Singh 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). > As discussing offline, I think this can make system to spend too much time in scan_folios() in moving the pages from Gen-0 to Gen-1 of the other zone which can result into OOM is not active when necessary. > 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@vger.kernel.org > 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> We tested this patch on our systems for couple of weeks and aggressive OOM is not observed which otherwise is easily reproducible. Tested-by: Charan Teja Kalla <quic_charante@quicinc.com>
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);
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@vger.kernel.org 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> --- Changes in v2: - Add Fixes tag and cc stable mm/vmscan.c | 18 ++++++++++++++---- 1 file changed, 14 insertions(+), 4 deletions(-)