On 2023/5/5 8:54, Yunsheng Lin wrote:
> It is not exactly the kind of refcnt bias trick in my mind, I was thinking
> about using pool->pages_state_hold_cnt as refcnt bias and merge it to
> pool->pages_state_release_cnt as needed, maybe I need to try to implement
> that to see if it turn out to be what I want it to be.
>
I did try implementing the above idea, not sure is there anything missing
yet as I only do the compile testing.
diff --git a/include/net/page_pool.h b/include/net/page_pool.h
index c8ec2f34722b..bd8dacc2adfd 100644
--- a/include/net/page_pool.h
+++ b/include/net/page_pool.h
@@ -50,6 +50,10 @@
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 +155,6 @@ 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 +164,7 @@ 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;
/*
@@ -206,8 +206,6 @@ struct page_pool {
* refcnt serves purpose is to simplify drivers error handling.
*/
refcount_t user_cnt;
-
- u64 destroy_cnt;
};
struct page *page_pool_alloc_pages(struct page_pool *pool, gfp_t gfp);
diff --git a/include/trace/events/page_pool.h b/include/trace/events/page_pool.h
index ca534501158b..200f539f1a70 100644
--- a/include/trace/events/page_pool.h
+++ b/include/trace/events/page_pool.h
@@ -23,7 +23,6 @@ TRACE_EVENT(page_pool_release,
__field(s32, inflight)
__field(u32, hold)
__field(u32, release)
- __field(u64, cnt)
),
TP_fast_assign(
@@ -31,12 +30,11 @@ TRACE_EVENT(page_pool_release,
__entry->inflight = inflight;
__entry->hold = hold;
__entry->release = release;
- __entry->cnt = pool->destroy_cnt;
),
- TP_printk("page_pool=%p inflight=%d hold=%u release=%u cnt=%llu",
+ TP_printk("page_pool=%p inflight=%d hold=%u release=%u",
__entry->pool, __entry->inflight, __entry->hold,
- __entry->release, __entry->cnt)
+ __entry->release)
);
TRACE_EVENT(page_pool_state_release,
diff --git a/net/core/page_pool.c b/net/core/page_pool.c
index e212e9d7edcb..6b3393f0c194 100644
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c
@@ -190,7 +190,8 @@ static int page_pool_init(struct page_pool *pool,
if (ptr_ring_init(&pool->ring, ring_qsize, GFP_KERNEL) < 0)
return -ENOMEM;
- atomic_set(&pool->pages_state_release_cnt, 0);
+ atomic_set(&pool->pages_state_release_cnt, INT_MAX / 2);
+ pool->pages_state_hold_cnt = INT_MAX / 2;
/* Driver calling page_pool_create() also call page_pool_destroy() */
refcount_set(&pool->user_cnt, 1);
@@ -344,6 +345,15 @@ static void page_pool_clear_pp_info(struct page *page)
page->pp = NULL;
}
+static void page_pool_hold_cnt_dec(struct page_pool *pool)
+{
+ if (likely(--pool->pages_state_hold_cnt))
+ return;
+
+ pool->pages_state_hold_cnt = INT_MAX / 2;
+ atomic_add(INT_MAX / 2, &pool->pages_state_release_cnt);
+}
+
static struct page *__page_pool_alloc_page_order(struct page_pool *pool,
gfp_t gfp)
{
@@ -364,7 +374,8 @@ static struct page *__page_pool_alloc_page_order(struct page_pool *pool,
page_pool_set_pp_info(pool, page);
/* Track how many pages are held 'in-flight' */
- pool->pages_state_hold_cnt++;
+ page_pool_hold_cnt_dec(pool);
+
trace_page_pool_state_hold(pool, page, pool->pages_state_hold_cnt);
return page;
}
@@ -410,7 +421,7 @@ static struct page *__page_pool_alloc_pages_slow(struct page_pool *pool,
page_pool_set_pp_info(pool, page);
pool->alloc.cache[pool->alloc.count++] = page;
/* Track how many pages are held 'in-flight' */
- pool->pages_state_hold_cnt++;
+ page_pool_hold_cnt_dec(pool);
trace_page_pool_state_hold(pool, page,
pool->pages_state_hold_cnt);
}
@@ -445,24 +456,8 @@ struct page *page_pool_alloc_pages(struct page_pool *pool, gfp_t gfp)
}
EXPORT_SYMBOL(page_pool_alloc_pages);
-/* Calculate distance between two u32 values, valid if distance is below 2^(31)
- * https://en.wikipedia.org/wiki/Serial_number_arithmetic#General_Solution
- */
-#define _distance(a, b) (s32)((a) - (b))
-
-static s32 page_pool_inflight(struct page_pool *pool)
-{
- u32 release_cnt = atomic_read(&pool->pages_state_release_cnt);
- u32 hold_cnt = READ_ONCE(pool->pages_state_hold_cnt);
- s32 inflight;
-
- inflight = _distance(hold_cnt, release_cnt);
- trace_page_pool_release(pool, inflight, hold_cnt, release_cnt);
- WARN(inflight < 0, "Negative(%d) inflight packet-pages", inflight);
-
- return inflight;
-}
+static void page_pool_free(struct page_pool *pool);
/* 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
@@ -493,8 +488,12 @@ void page_pool_release_page(struct page_pool *pool, struct page *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);
+ count = atomic_dec_return_relaxed(&pool->pages_state_release_cnt);
+
trace_page_pool_state_release(pool, page, count);
+
+ if (unlikely(!count))
+ page_pool_free(pool);
}
EXPORT_SYMBOL(page_pool_release_page);
@@ -513,11 +512,20 @@ static void page_pool_return_page(struct page_pool *pool, struct page *page)
static bool page_pool_recycle_in_ring(struct page_pool *pool, struct page *page)
{
int ret;
- /* BH protection not needed if current is softirq */
- if (in_softirq())
- ret = ptr_ring_produce(&pool->ring, page);
- else
- ret = ptr_ring_produce_bh(&pool->ring, page);
+
+ page_pool_ring_lock(pool);
+
+ /* Do the check within spinlock to pair with flags setting
+ * in page_pool_destroy().
+ */
+ if (unlikely(pool->p.flags & PP_FLAG_SHUTDOWN)) {
+ page_pool_ring_unlock(pool);
+ return false;
+ }
+
+ ret = __ptr_ring_produce(&pool->ring, page);
+
+ page_pool_ring_unlock(pool);
if (!ret) {
recycle_stat_inc(pool, ring);
@@ -634,9 +642,20 @@ void page_pool_put_page_bulk(struct page_pool *pool, void **data,
if (unlikely(!bulk_len))
return;
+ i = 0;
+
/* Bulk producer into ptr_ring page_pool cache */
page_pool_ring_lock(pool);
- for (i = 0; i < bulk_len; i++) {
+
+ /* Do the check within spinlock to pair with flags setting
+ * in page_pool_destroy().
+ */
+ if (unlikely(pool->p.flags & PP_FLAG_SHUTDOWN)) {
+ page_pool_ring_unlock(pool);
+ goto return_page;
+ }
+
+ for (; i < bulk_len; i++) {
if (__ptr_ring_produce(&pool->ring, data[i])) {
/* ring full */
recycle_stat_inc(pool, ring_full);
@@ -650,8 +669,10 @@ void page_pool_put_page_bulk(struct page_pool *pool, void **data,
if (likely(i == bulk_len))
return;
- /* ptr_ring cache full, free remaining pages outside producer lock
- * since put_page() with refcnt == 1 can be an expensive operation
+return_page:
+ /* ptr_ring cache full or in shutdown mode, free remaining pages
+ * outside producer lock since put_page() with refcnt == 1 can
+ * be an expensive operation
*/
for (; i < bulk_len; i++)
page_pool_return_page(pool, data[i]);
@@ -768,13 +789,10 @@ static void page_pool_free(struct page_pool *pool)
kfree(pool);
}
-static void page_pool_empty_alloc_cache_once(struct page_pool *pool)
+static void page_pool_scrub(struct page_pool *pool)
{
struct page *page;
- if (pool->destroy_cnt)
- return;
-
/* Empty alloc cache, assume caller made sure this is
* no-longer in use, and page_pool_alloc_pages() cannot be
* call concurrently.
@@ -785,52 +803,6 @@ static void page_pool_empty_alloc_cache_once(struct page_pool *pool)
}
}
-static void page_pool_scrub(struct page_pool *pool)
-{
- page_pool_empty_alloc_cache_once(pool);
- pool->destroy_cnt++;
-
- /* No more consumers should exist, but producers could still
- * be in-flight.
- */
- page_pool_empty_ring(pool);
-}
-
-static int page_pool_release(struct page_pool *pool)
-{
- int inflight;
-
- page_pool_scrub(pool);
- inflight = page_pool_inflight(pool);
- if (!inflight)
- page_pool_free(pool);
-
- return inflight;
-}
-
-static void page_pool_release_retry(struct work_struct *wq)
-{
- 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);
- 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;
- }
-
- /* Still not ready to be disconnected, retry later */
- schedule_delayed_work(&pool->release_dw, DEFER_TIME);
-}
-
void page_pool_use_xdp_mem(struct page_pool *pool, void (*disconnect)(void *),
struct xdp_mem_info *mem)
{
@@ -864,15 +836,25 @@ void page_pool_destroy(struct page_pool *pool)
page_pool_unlink_napi(pool);
page_pool_free_frag(pool);
+ page_pool_scrub(pool);
- if (!page_pool_release(pool))
- return;
+ /* when page_pool_destroy() is called, it is assumed that no
+ * page will be recycled to pool->alloc cache, we only need to
+ * make sure no page will be recycled to pool->ring by setting
+ * PP_FLAG_SHUTDOWN within spinlock to pair with flags checking
+ * within spinlock.
+ */
+ page_pool_ring_lock(pool);
+ pool->p.flags |= PP_FLAG_SHUTDOWN;
+ page_pool_ring_unlock(pool);
- pool->defer_start = jiffies;
- pool->defer_warn = jiffies + DEFER_WARN_INTERVAL;
+ page_pool_empty_ring(pool);
+
+ if (atomic_sub_return_relaxed(pool->pages_state_hold_cnt,
+ &pool->pages_state_release_cnt))
+ return;
- INIT_DELAYED_WORK(&pool->release_dw, page_pool_release_retry);
- schedule_delayed_work(&pool->release_dw, DEFER_TIME);
+ page_pool_free(pool);
}
EXPORT_SYMBOL(page_pool_destroy);
