This removes the workqueue scheme that periodically tests when inflight reach zero such that page_pool memory can be freed. This change adds code to fast-path free checking for a shutdown flags bit after returning PP pages. Performance is very important for PP, as the fast path is used for XDP_DROP use-cases where NIC drivers recycle PP pages directly into PP alloc cache. This patch (since V3) shows zero impact on this fast path. Micro benchmarked with [1] on Intel CPU E5-1650 @3.60GHz. The slight code reorg of likely() are deliberate. [1] https://github.com/netoptimizer/prototype-kernel/blob/master/kernel/lib/bench_page_pool_simple.c Signed-off-by: Jesper Dangaard Brouer <brouer@xxxxxxxxxx> --- include/net/page_pool.h | 10 ++- net/core/page_pool.c | 138 ++++++++++++++++++++++++++++++++++------------- 2 files changed, 104 insertions(+), 44 deletions(-) diff --git a/include/net/page_pool.h b/include/net/page_pool.h index c8ec2f34722b..19396e05f12d 100644 --- a/include/net/page_pool.h +++ b/include/net/page_pool.h @@ -50,6 +50,9 @@ PP_FLAG_DMA_SYNC_DEV |\ PP_FLAG_PAGE_FRAG) +/* Internal flag: PP in shutdown phase, waiting for inflight pages */ +#define PP_FLAG_SHUTDOWN BIT(8) + /* * Fast allocation side cache array/stack * @@ -151,11 +154,6 @@ static inline u64 *page_pool_ethtool_stats_get(u64 *data, void *stats) struct page_pool { struct page_pool_params p; - struct delayed_work release_dw; - void (*disconnect)(void *); - unsigned long defer_start; - unsigned long defer_warn; - u32 pages_state_hold_cnt; unsigned int frag_offset; struct page *frag_page; @@ -165,6 +163,7 @@ struct page_pool { /* these stats are incremented while in softirq context */ struct page_pool_alloc_stats alloc_stats; #endif + void (*disconnect)(void *); u32 xdp_mem_id; /* @@ -208,6 +207,7 @@ struct page_pool { refcount_t user_cnt; u64 destroy_cnt; + struct rcu_head rcu; }; struct page *page_pool_alloc_pages(struct page_pool *pool, gfp_t gfp); diff --git a/net/core/page_pool.c b/net/core/page_pool.c index e212e9d7edcb..213349148a48 100644 --- a/net/core/page_pool.c +++ b/net/core/page_pool.c @@ -23,9 +23,6 @@ #include <trace/events/page_pool.h> -#define DEFER_TIME (msecs_to_jiffies(1000)) -#define DEFER_WARN_INTERVAL (60 * HZ) - #define BIAS_MAX LONG_MAX #ifdef CONFIG_PAGE_POOL_STATS @@ -380,6 +377,10 @@ static struct page *__page_pool_alloc_pages_slow(struct page_pool *pool, struct page *page; int i, nr_pages; + /* API usage BUG: PP in shutdown phase, cannot alloc new pages */ + if (WARN_ON(pool->p.flags & PP_FLAG_SHUTDOWN)) + return NULL; + /* Don't support bulk alloc for high-order pages */ if (unlikely(pp_order)) return __page_pool_alloc_page_order(pool, gfp); @@ -450,9 +451,8 @@ EXPORT_SYMBOL(page_pool_alloc_pages); */ #define _distance(a, b) (s32)((a) - (b)) -static s32 page_pool_inflight(struct page_pool *pool) +static s32 __page_pool_inflight(struct page_pool *pool, u32 release_cnt) { - u32 release_cnt = atomic_read(&pool->pages_state_release_cnt); u32 hold_cnt = READ_ONCE(pool->pages_state_hold_cnt); s32 inflight; @@ -464,6 +464,14 @@ static s32 page_pool_inflight(struct page_pool *pool) return inflight; } +static s32 page_pool_inflight(struct page_pool *pool) +{ + u32 release_cnt = atomic_read(&pool->pages_state_release_cnt); + return __page_pool_inflight(pool, release_cnt); +} + +static int page_pool_free_attempt(struct page_pool *pool, u32 release_cnt); + /* Disconnects a page (from a page_pool). API users can have a need * to disconnect a page (from a page_pool), to allow it to be used as * a regular page (that will eventually be returned to the normal @@ -472,7 +480,7 @@ static s32 page_pool_inflight(struct page_pool *pool) void page_pool_release_page(struct page_pool *pool, struct page *page) { dma_addr_t dma; - int count; + u32 release_cnt; if (!(pool->p.flags & PP_FLAG_DMA_MAP)) /* Always account for inflight pages, even if we didn't @@ -490,11 +498,12 @@ void page_pool_release_page(struct page_pool *pool, struct page *page) skip_dma_unmap: page_pool_clear_pp_info(page); - /* This may be the last page returned, releasing the pool, so - * it is not safe to reference pool afterwards. - */ - count = atomic_inc_return_relaxed(&pool->pages_state_release_cnt); - trace_page_pool_state_release(pool, page, count); + release_cnt = atomic_inc_return(&pool->pages_state_release_cnt); + trace_page_pool_state_release(pool, page, release_cnt); + + /* In shutdown phase, last page will free pool instance */ + if (READ_ONCE(pool->p.flags) & PP_FLAG_SHUTDOWN) + page_pool_free_attempt(pool, release_cnt); } EXPORT_SYMBOL(page_pool_release_page); @@ -535,7 +544,7 @@ static bool page_pool_recycle_in_ring(struct page_pool *pool, struct page *page) static bool page_pool_recycle_in_cache(struct page *page, struct page_pool *pool) { - if (unlikely(pool->alloc.count == PP_ALLOC_CACHE_SIZE)) { + if (pool->alloc.count == PP_ALLOC_CACHE_SIZE) { recycle_stat_inc(pool, cache_full); return false; } @@ -546,6 +555,8 @@ static bool page_pool_recycle_in_cache(struct page *page, return true; } +static void page_pool_empty_ring(struct page_pool *pool); + /* If the page refcnt == 1, this will try to recycle the page. * if PP_FLAG_DMA_SYNC_DEV is set, we'll try to sync the DMA area for * the configured size min(dma_sync_size, pool->max_len). @@ -572,7 +583,8 @@ __page_pool_put_page(struct page_pool *pool, struct page *page, page_pool_dma_sync_for_device(pool, page, dma_sync_size); - if (allow_direct && in_softirq() && + /* During PP shutdown, no direct recycle must occur */ + if (likely(allow_direct && in_softirq()) && page_pool_recycle_in_cache(page, pool)) return NULL; @@ -609,6 +621,8 @@ void page_pool_put_defragged_page(struct page_pool *pool, struct page *page, recycle_stat_inc(pool, ring_full); page_pool_return_page(pool, page); } + if (page && pool->p.flags & PP_FLAG_SHUTDOWN) + page_pool_empty_ring(pool); } EXPORT_SYMBOL(page_pool_put_defragged_page); @@ -646,6 +660,9 @@ void page_pool_put_page_bulk(struct page_pool *pool, void **data, recycle_stat_add(pool, ring, i); page_pool_ring_unlock(pool); + if (pool->p.flags & PP_FLAG_SHUTDOWN) + page_pool_empty_ring(pool); + /* Hopefully all pages was return into ptr_ring */ if (likely(i == bulk_len)) return; @@ -737,12 +754,18 @@ struct page *page_pool_alloc_frag(struct page_pool *pool, } EXPORT_SYMBOL(page_pool_alloc_frag); +noinline static void page_pool_empty_ring(struct page_pool *pool) { - struct page *page; + struct page *page, *next; + + next = ptr_ring_consume_bh(&pool->ring); /* Empty recycle ring */ - while ((page = ptr_ring_consume_bh(&pool->ring))) { + while (next) { + page = next; + next = ptr_ring_consume_bh(&pool->ring); + /* Verify the refcnt invariant of cached pages */ if (!(page_ref_count(page) == 1)) pr_crit("%s() page_pool refcnt %d violation\n", @@ -768,6 +791,14 @@ static void page_pool_free(struct page_pool *pool) kfree(pool); } +static void page_pool_free_rcu(struct rcu_head *rcu) +{ + struct page_pool *pool; + + pool = container_of(rcu, struct page_pool, rcu); + page_pool_free(pool); +} + static void page_pool_empty_alloc_cache_once(struct page_pool *pool) { struct page *page; @@ -796,39 +827,30 @@ static void page_pool_scrub(struct page_pool *pool) page_pool_empty_ring(pool); } -static int page_pool_release(struct page_pool *pool) +noinline +static int page_pool_free_attempt(struct page_pool *pool, u32 release_cnt) { int inflight; - page_pool_scrub(pool); - inflight = page_pool_inflight(pool); + rcu_read_lock(); + inflight = __page_pool_inflight(pool, release_cnt); + rcu_read_unlock(); if (!inflight) - page_pool_free(pool); + call_rcu(&pool->rcu, page_pool_free_rcu); return inflight; } -static void page_pool_release_retry(struct work_struct *wq) +static int page_pool_release(struct page_pool *pool) { - struct delayed_work *dwq = to_delayed_work(wq); - struct page_pool *pool = container_of(dwq, typeof(*pool), release_dw); int inflight; - inflight = page_pool_release(pool); + page_pool_scrub(pool); + inflight = page_pool_inflight(pool); if (!inflight) - return; - - /* Periodic warning */ - if (time_after_eq(jiffies, pool->defer_warn)) { - int sec = (s32)((u32)jiffies - (u32)pool->defer_start) / HZ; - - pr_warn("%s() stalled pool shutdown %d inflight %d sec\n", - __func__, inflight, sec); - pool->defer_warn = jiffies + DEFER_WARN_INTERVAL; - } + page_pool_free(pool); - /* Still not ready to be disconnected, retry later */ - schedule_delayed_work(&pool->release_dw, DEFER_TIME); + return inflight; } void page_pool_use_xdp_mem(struct page_pool *pool, void (*disconnect)(void *), @@ -856,6 +878,10 @@ EXPORT_SYMBOL(page_pool_unlink_napi); void page_pool_destroy(struct page_pool *pool) { + unsigned int flags; + u32 release_cnt; + u32 hold_cnt; + if (!pool) return; @@ -868,11 +894,45 @@ void page_pool_destroy(struct page_pool *pool) if (!page_pool_release(pool)) return; - pool->defer_start = jiffies; - pool->defer_warn = jiffies + DEFER_WARN_INTERVAL; + /* PP have pages inflight, thus cannot immediately release memory. + * Enter into shutdown phase, depending on remaining in-flight PP + * pages to trigger shutdown process (on concurrent CPUs) and last + * page will free pool instance. + * + * There exist two race conditions here, we need to take into + * account in the following code. + * + * 1. Before setting PP_FLAG_SHUTDOWN another CPU released the last + * pages into the ptr_ring. Thus, it missed triggering shutdown + * process, which can then be stalled forever. + * + * 2. After setting PP_FLAG_SHUTDOWN another CPU released the last + * page, which triggered shutdown process and freed pool + * instance. Thus, its not safe to dereference *pool afterwards. + * + * Handling races by holding a fake in-flight count, via artificially + * bumping pages_state_hold_cnt, which assures pool isn't freed under + * us. Use RCU Grace-Periods to guarantee concurrent CPUs will + * transition safely into the shutdown phase. + * + * After safely transition into this state the races are resolved. For + * race(1) its safe to recheck and empty ptr_ring (it will not free + * pool). Race(2) cannot happen, and we can release fake in-flight count + * as last step. + */ + hold_cnt = READ_ONCE(pool->pages_state_hold_cnt) + 1; + WRITE_ONCE(pool->pages_state_hold_cnt, hold_cnt); + synchronize_rcu(); + + flags = READ_ONCE(pool->p.flags) | PP_FLAG_SHUTDOWN; + WRITE_ONCE(pool->p.flags, flags); + synchronize_rcu(); + + /* Concurrent CPUs could have returned last pages into ptr_ring */ + page_pool_empty_ring(pool); - INIT_DELAYED_WORK(&pool->release_dw, page_pool_release_retry); - schedule_delayed_work(&pool->release_dw, DEFER_TIME); + release_cnt = atomic_inc_return(&pool->pages_state_release_cnt); + page_pool_free_attempt(pool, release_cnt); } EXPORT_SYMBOL(page_pool_destroy);
