Re: [PATCH] kswapd: no need reclaim cma pages triggered by unmovable allocation

Michal Hocko
2021-02-09T09:29:15Z

On Tue 09-02-21 16:23:13, zhou wrote:
> From: zhou xianrong <xianrong.zhou@transsion.com>
>
> For purpose of better migration cma pages are allocated after
> failure movalbe allocations and are used normally for file pages
> or anonymous pages.
>
> In reclaim path so many cma pages if configurated are reclaimed
> from lru lists in kswapd mainly or direct reclaim triggered by
> unmovable or reclaimable allocations. But these cma pages can not
> be used by original unmovable or reclaimable allocations. So the
> reclaim are unnecessary.
>
> In a same system if the cma pages were configurated to large then
> more failture unmovable (vmalloc etc.) or reclaimable (slab etc.)
> allocations are arised and then more kswapd rounds are triggered
> and then more cma pages are reclaimed.

Could you be more specific? Do you have any numbers and an example
configuration when this is visible?

> So this maybe cause vicious cycle. It causes that when we are under
> low memory and still there are many cma pages that can not be
> allocated due to unnecessary cma reclaim and cma fallback allocations
> . So cma pages are not used sufficiently.
>
> The modification is straightforward that skips reclaiming cma pages
> in reclaim procedure which is triggered only by unmovable or
> reclaimable allocations. This optimization can avoid ~3% unnecessary
> cma isolations (cma isolated / total isolated).

Joonsoo used to have a patch series to drop many of the hacks we have
for CMA and made it part of a movable zone. That would solve many
problems, including this one. I am not sure where the work stands now
but it would be probably better to revive that rather than adding more
special casing on top of what we have right now.

> Signed-off-by: zhou xianrong <xianrong.zhou@transsion.com>
> ---
> include/linux/mmzone.h | 6 ++--
> include/trace/events/vmscan.h | 20 +++++++----
> mm/page_alloc.c | 5 +--
> mm/vmscan.c | 63 +++++++++++++++++++++++++++++------
> 4 files changed, 73 insertions(+), 21 deletions(-)
>
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index b593316bff3d..7dd38d7372b9 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -301,6 +301,8 @@ struct lruvec {
> #define ISOLATE_ASYNC_MIGRATE ((__force isolate_mode_t)0x4)
> /* Isolate unevictable pages */
> #define ISOLATE_UNEVICTABLE ((__force isolate_mode_t)0x8)
> +/* Isolate none cma pages */
> +#define ISOLATE_NONCMA ((__force isolate_mode_t)0x10)
>
> /* LRU Isolation modes. */
> typedef unsigned __bitwise isolate_mode_t;
> @@ -756,7 +758,7 @@ typedef struct pglist_data {
> wait_queue_head_t pfmemalloc_wait;
> struct task_struct *kswapd; /* Protected by
> mem_hotplug_begin/end() */
> - int kswapd_order;
> + int kswapd_order, kswapd_migratetype;
> enum zone_type kswapd_highest_zoneidx;
>
> int kswapd_failures; /* Number of 'reclaimed == 0' runs */
> @@ -840,7 +842,7 @@ static inline bool pgdat_is_empty(pg_data_t *pgdat)
>
> void build_all_zonelists(pg_data_t *pgdat);
> void wakeup_kswapd(struct zone *zone, gfp_t gfp_mask, int order,
> - enum zone_type highest_zoneidx);
> + int migratetype, enum zone_type highest_zoneidx);
> bool __zone_watermark_ok(struct zone *z, unsigned int order, unsigned long mark,
> int highest_zoneidx, unsigned int alloc_flags,
> long free_pages);
> diff --git a/include/trace/events/vmscan.h b/include/trace/events/vmscan.h
> index 2070df64958e..41bbafdfde84 100644
> --- a/include/trace/events/vmscan.h
> +++ b/include/trace/events/vmscan.h
> @@ -51,37 +51,41 @@ TRACE_EVENT(mm_vmscan_kswapd_sleep,
>
> TRACE_EVENT(mm_vmscan_kswapd_wake,
>
> - TP_PROTO(int nid, int zid, int order),
> + TP_PROTO(int nid, int zid, int order, int mt),
>
> - TP_ARGS(nid, zid, order),
> + TP_ARGS(nid, zid, order, mt),
>
> TP_STRUCT__entry(
> __field( int, nid )
> __field( int, zid )
> __field( int, order )
> + __field( int, mt )
> ),
>
> TP_fast_assign(
> __entry->nid = nid;
> __entry->zid = zid;
> __entry->order = order;
> + __entry->mt = mt;
> ),
>
> - TP_printk("nid=%d order=%d",
> + TP_printk("nid=%d order=%d migratetype=%d",
> __entry->nid,
> - __entry->order)
> + __entry->order,
> + __entry->mt)
> );
>
> TRACE_EVENT(mm_vmscan_wakeup_kswapd,
>
> - TP_PROTO(int nid, int zid, int order, gfp_t gfp_flags),
> + TP_PROTO(int nid, int zid, int order, int mt, gfp_t gfp_flags),
>
> - TP_ARGS(nid, zid, order, gfp_flags),
> + TP_ARGS(nid, zid, order, mt, gfp_flags),
>
> TP_STRUCT__entry(
> __field( int, nid )
> __field( int, zid )
> __field( int, order )
> + __field( int, mt )
> __field( gfp_t, gfp_flags )
> ),
>
> @@ -89,12 +93,14 @@ TRACE_EVENT(mm_vmscan_wakeup_kswapd,
> __entry->nid = nid;
> __entry->zid = zid;
> __entry->order = order;
> + __entry->mt = mt;
> __entry->gfp_flags = gfp_flags;
> ),
>
> - TP_printk("nid=%d order=%d gfp_flags=%s",
> + TP_printk("nid=%d order=%d migratetype=%d gfp_flags=%s",
> __entry->nid,
> __entry->order,
> + __entry->mt,
> show_gfp_flags(__entry->gfp_flags))
> );
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 519a60d5b6f7..45ceb15721b8 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -3517,7 +3517,7 @@ struct page *rmqueue(struct zone *preferred_zone,
> /* Separate test+clear to avoid unnecessary atomics */
> if (test_bit(ZONE_BOOSTED_WATERMARK, &zone->flags)) {
> clear_bit(ZONE_BOOSTED_WATERMARK, &zone->flags);
> - wakeup_kswapd(zone, 0, 0, zone_idx(zone));
> + wakeup_kswapd(zone, 0, 0, migratetype, zone_idx(zone));
> }
>
> VM_BUG_ON_PAGE(page && bad_range(zone, page), page);
> @@ -4426,11 +4426,12 @@ static void wake_all_kswapds(unsigned int order, gfp_t gfp_mask,
> struct zone *zone;
> pg_data_t *last_pgdat = NULL;
> enum zone_type highest_zoneidx = ac->highest_zoneidx;
> + int migratetype = ac->migratetype;
>
> for_each_zone_zonelist_nodemask(zone, z, ac->zonelist, highest_zoneidx,
> ac->nodemask) {
> if (last_pgdat != zone->zone_pgdat)
> - wakeup_kswapd(zone, gfp_mask, order, highest_zoneidx);
> + wakeup_kswapd(zone, gfp_mask, order, migratetype, highest_zoneidx);
> last_pgdat = zone->zone_pgdat;
> }
> }
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index b1b574ad199d..e61ec8747a40 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -99,6 +99,9 @@ struct scan_control {
> /* Can pages be swapped as part of reclaim? */
> unsigned int may_swap:1;
>
> + /* Can cma pages be reclaimed? */
> + unsigned int may_cma:1;
> +
> /*
> * Cgroups are not reclaimed below their configured memory.low,
> * unless we threaten to OOM. If any cgroups are skipped due to
> @@ -286,6 +289,11 @@ static bool writeback_throttling_sane(struct scan_control *sc)
> }
> #endif
>
> +static bool movable_reclaim(gfp_t gfp_mask)
> +{
> + return is_migrate_movable(gfp_migratetype(gfp_mask));
> +}
> +
> /*
> * This misses isolated pages which are not accounted for to save counters.
> * As the data only determines if reclaim or compaction continues, it is
> @@ -1499,6 +1507,7 @@ unsigned int reclaim_clean_pages_from_list(struct zone *zone,
> .gfp_mask = GFP_KERNEL,
> .priority = DEF_PRIORITY,
> .may_unmap = 1,
> + .may_cma = 1,
> };
> struct reclaim_stat stat;
> unsigned int nr_reclaimed;
> @@ -1593,6 +1602,9 @@ int __isolate_lru_page_prepare(struct page *page, isolate_mode_t mode)
> if ((mode & ISOLATE_UNMAPPED) && page_mapped(page))
> return ret;
>
> + if ((mode & ISOLATE_NONCMA) && is_migrate_cma(get_pageblock_migratetype(page)))
> + return ret;
> +
> return 0;
> }
>
> @@ -1647,7 +1659,10 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
> unsigned long skipped = 0;
> unsigned long scan, total_scan, nr_pages;
> LIST_HEAD(pages_skipped);
> - isolate_mode_t mode = (sc->may_unmap ? 0 : ISOLATE_UNMAPPED);
> + isolate_mode_t mode;
> +
> + mode = (sc->may_unmap ? 0 : ISOLATE_UNMAPPED);
> + mode |= (sc->may_cma ? 0 : ISOLATE_NONCMA);
>
> total_scan = 0;
> scan = 0;
> @@ -2125,6 +2140,7 @@ unsigned long reclaim_pages(struct list_head *page_list)
> .may_writepage = 1,
> .may_unmap = 1,
> .may_swap = 1,
> + .may_cma = 1,
> };
>
> while (!list_empty(page_list)) {
> @@ -3253,6 +3269,7 @@ unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
> .may_writepage = !laptop_mode,
> .may_unmap = 1,
> .may_swap = 1,
> + .may_cma = movable_reclaim(gfp_mask),
> };
>
> /*
> @@ -3298,6 +3315,7 @@ unsigned long mem_cgroup_shrink_node(struct mem_cgroup *memcg,
> .may_unmap = 1,
> .reclaim_idx = MAX_NR_ZONES - 1,
> .may_swap = !noswap,
> + .may_cma = 1,
> };
>
> WARN_ON_ONCE(!current->reclaim_state);
> @@ -3341,6 +3359,7 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
> .may_writepage = !laptop_mode,
> .may_unmap = 1,
> .may_swap = may_swap,
> + .may_cma = 1,
> };
> /*
> * Traverse the ZONELIST_FALLBACK zonelist of the current node to put
> @@ -3548,7 +3567,7 @@ static bool kswapd_shrink_node(pg_data_t *pgdat,
> * or lower is eligible for reclaim until at least one usable zone is
> * balanced.
> */
> -static int balance_pgdat(pg_data_t *pgdat, int order, int highest_zoneidx)
> +static int balance_pgdat(pg_data_t *pgdat, int order, int migratetype, int highest_zoneidx)
> {
> int i;
> unsigned long nr_soft_reclaimed;
> @@ -3650,6 +3669,7 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int highest_zoneidx)
> */
> sc.may_writepage = !laptop_mode && !nr_boost_reclaim;
> sc.may_swap = !nr_boost_reclaim;
> + sc.may_cma = is_migrate_movable(migratetype);
>
> /*
> * Do some background aging of the anon list, to give
> @@ -3771,8 +3791,15 @@ static enum zone_type kswapd_highest_zoneidx(pg_data_t *pgdat,
> return curr_idx == MAX_NR_ZONES ? prev_highest_zoneidx : curr_idx;
> }
>
> +static int kswapd_migratetype(pg_data_t *pgdat, int prev_migratetype)
> +{
> + int curr_migratetype = READ_ONCE(pgdat->kswapd_migratetype);
> +
> + return curr_migratetype == MIGRATE_TYPES ? prev_migratetype : curr_migratetype;
> +}
> +
> static void kswapd_try_to_sleep(pg_data_t *pgdat, int alloc_order, int reclaim_order,
> - unsigned int highest_zoneidx)
> + int migratetype, unsigned int highest_zoneidx)
> {
> long remaining = 0;
> DEFINE_WAIT(wait);
> @@ -3807,8 +3834,8 @@ static void kswapd_try_to_sleep(pg_data_t *pgdat, int alloc_order, int reclaim_o
> remaining = schedule_timeout(HZ/10);
>
> /*
> - * If woken prematurely then reset kswapd_highest_zoneidx and
> - * order. The values will either be from a wakeup request or
> + * If woken prematurely then reset kswapd_highest_zoneidx, order
> + * and migratetype. The values will either be from a wakeup request or
> * the previous request that slept prematurely.
> */
> if (remaining) {
> @@ -3818,6 +3845,10 @@ static void kswapd_try_to_sleep(pg_data_t *pgdat, int alloc_order, int reclaim_o
>
> if (READ_ONCE(pgdat->kswapd_order) < reclaim_order)
> WRITE_ONCE(pgdat->kswapd_order, reclaim_order);
> +
> + if (!is_migrate_movable(READ_ONCE(pgdat->kswapd_migratetype)))
> + WRITE_ONCE(pgdat->kswapd_migratetype,
> + kswapd_migratetype(pgdat, migratetype));
> }
>
> finish_wait(&pgdat->kswapd_wait, &wait);
> @@ -3870,6 +3901,7 @@ static void kswapd_try_to_sleep(pg_data_t *pgdat, int alloc_order, int reclaim_o
> */
> static int kswapd(void *p)
> {
> + int migratetype = 0;
> unsigned int alloc_order, reclaim_order;
> unsigned int highest_zoneidx = MAX_NR_ZONES - 1;
> pg_data_t *pgdat = (pg_data_t*)p;
> @@ -3895,23 +3927,27 @@ static int kswapd(void *p)
> set_freezable();
>
> WRITE_ONCE(pgdat->kswapd_order, 0);
> + WRITE_ONCE(pgdat->kswapd_migratetype, MIGRATE_TYPES);
> WRITE_ONCE(pgdat->kswapd_highest_zoneidx, MAX_NR_ZONES);
> for ( ; ; ) {
> bool ret;
>
> alloc_order = reclaim_order = READ_ONCE(pgdat->kswapd_order);
> + migratetype = kswapd_migratetype(pgdat, migratetype);
> highest_zoneidx = kswapd_highest_zoneidx(pgdat,
> highest_zoneidx);
>
> kswapd_try_sleep:
> kswapd_try_to_sleep(pgdat, alloc_order, reclaim_order,
> - highest_zoneidx);
> + migratetype, highest_zoneidx);
>
> /* Read the new order and highest_zoneidx */
> alloc_order = READ_ONCE(pgdat->kswapd_order);
> + migratetype = kswapd_migratetype(pgdat, migratetype);
> highest_zoneidx = kswapd_highest_zoneidx(pgdat,
> highest_zoneidx);
> WRITE_ONCE(pgdat->kswapd_order, 0);
> + WRITE_ONCE(pgdat->kswapd_migratetype, MIGRATE_TYPES);
> WRITE_ONCE(pgdat->kswapd_highest_zoneidx, MAX_NR_ZONES);
>
> ret = try_to_freeze();
> @@ -3934,8 +3970,8 @@ static int kswapd(void *p)
> * request (alloc_order).
> */
> trace_mm_vmscan_kswapd_wake(pgdat->node_id, highest_zoneidx,
> - alloc_order);
> - reclaim_order = balance_pgdat(pgdat, alloc_order,
> + alloc_order, migratetype);
> + reclaim_order = balance_pgdat(pgdat, alloc_order, migratetype,
> highest_zoneidx);
> if (reclaim_order < alloc_order)
> goto kswapd_try_sleep;
> @@ -3954,10 +3990,11 @@ static int kswapd(void *p)
> * needed.
> */
> void wakeup_kswapd(struct zone *zone, gfp_t gfp_flags, int order,
> - enum zone_type highest_zoneidx)
> + int migratetype, enum zone_type highest_zoneidx)
> {
> pg_data_t *pgdat;
> enum zone_type curr_idx;
> + int curr_migratetype;
>
> if (!managed_zone(zone))
> return;
> @@ -3967,6 +4004,7 @@ void wakeup_kswapd(struct zone *zone, gfp_t gfp_flags, int order,
>
> pgdat = zone->zone_pgdat;
> curr_idx = READ_ONCE(pgdat->kswapd_highest_zoneidx);
> + curr_migratetype = READ_ONCE(pgdat->kswapd_migratetype);
>
> if (curr_idx == MAX_NR_ZONES || curr_idx < highest_zoneidx)
> WRITE_ONCE(pgdat->kswapd_highest_zoneidx, highest_zoneidx);
> @@ -3974,6 +4012,9 @@ void wakeup_kswapd(struct zone *zone, gfp_t gfp_flags, int order,
> if (READ_ONCE(pgdat->kswapd_order) < order)
> WRITE_ONCE(pgdat->kswapd_order, order);
>
> + if (curr_migratetype == MIGRATE_TYPES || is_migrate_movable(migratetype))
> + WRITE_ONCE(pgdat->kswapd_migratetype, migratetype);
> +
> if (!waitqueue_active(&pgdat->kswapd_wait))
> return;
>
> @@ -3994,7 +4035,7 @@ void wakeup_kswapd(struct zone *zone, gfp_t gfp_flags, int order,
> }
>
> trace_mm_vmscan_wakeup_kswapd(pgdat->node_id, highest_zoneidx, order,
> - gfp_flags);
> + migratetype, gfp_flags);
> wake_up_interruptible(&pgdat->kswapd_wait);
> }
>
> @@ -4017,6 +4058,7 @@ unsigned long shrink_all_memory(unsigned long nr_to_reclaim)
> .may_writepage = 1,
> .may_unmap = 1,
> .may_swap = 1,
> + .may_cma = 1,
> .hibernation_mode = 1,
> };
> struct zonelist *zonelist = node_zonelist(numa_node_id(), sc.gfp_mask);
> @@ -4176,6 +4218,7 @@ static int __node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned in
> .may_writepage = !!(node_reclaim_mode & RECLAIM_WRITE),
> .may_unmap = !!(node_reclaim_mode & RECLAIM_UNMAP),
> .may_swap = 1,
> + .may_cma = movable_reclaim(gfp_mask),
> .reclaim_idx = gfp_zone(gfp_mask),
> };
>
> --
> 2.25.1

--
Michal Hocko
SUSE Labs