From 779f4c5754c5a9d30dfe909fad2a2546afd70621 Mon Sep 17 00:00:00 2001
From: Jens Axboe <axboe@kernel.dk>
Date: Fri, 19 Feb 2021 12:33:30 -0700
Subject: io-wq: make hashed work map + lock per-ctx

Before the io-wq thread change, we maintained a hash work map and lock
per-node per-ring. That wasn't ideal, as we really wanted it to be per
ring. But now that we have per-task workers, the hash map ends up being
just per-task. That'll work just fine for the normal case of having
one task use a ring, but if you share the ring between tasks, then it's
considerably worse than it was before.

Make the hash map per ctx instead, which provides full per-ctx buffered
write serialization on hashed writes.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 fs/io-wq.c    | 10 ++++++----
 fs/io-wq.h    |  2 ++
 fs/io_uring.c |  4 ++++
 3 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/fs/io-wq.c b/fs/io-wq.c
index b0d09f60200b..9d5ab6d744dc 100644
--- a/fs/io-wq.c
+++ b/fs/io-wq.c
@@ -85,7 +85,6 @@ struct io_wqe {
 	struct {
 		raw_spinlock_t lock;
 		struct io_wq_work_list work_list;
-		unsigned long hash_map;
 		unsigned flags;
 	} ____cacheline_aligned_in_smp;
 
@@ -111,6 +110,9 @@ struct io_wq {
 
 	struct task_struct *manager;
 	struct user_struct *user;
+
+	unsigned long *hash_map;
+
 	refcount_t refs;
 	struct completion done;
 
@@ -353,8 +355,7 @@ static struct io_wq_work *io_get_next_work(struct io_wqe *wqe)
 
 		/* hashed, can run if not already running */
 		hash = io_get_work_hash(work);
-		if (!(wqe->hash_map & BIT(hash))) {
-			wqe->hash_map |= BIT(hash);
+		if (!test_and_set_bit(hash, wqe->wq->hash_map)) {
 			/* all items with this hash lie in [work, tail] */
 			tail = wqe->hash_tail[hash];
 			wqe->hash_tail[hash] = NULL;
@@ -452,7 +453,7 @@ get_next:
 
 			if (hash != -1U && !next_hashed) {
 				raw_spin_lock_irq(&wqe->lock);
-				wqe->hash_map &= ~BIT_ULL(hash);
+				clear_bit(hash, wq->hash_map);
 				wqe->flags &= ~IO_WQE_FLAG_STALLED;
 				/* skip unnecessary unlock-lock wqe->lock */
 				if (!work)
@@ -975,6 +976,7 @@ struct io_wq *io_wq_create(unsigned bounded, struct io_wq_data *data)
 	if (ret)
 		goto err_wqes;
 
+	wq->hash_map = data->hash_map;
 	wq->free_work = data->free_work;
 	wq->do_work = data->do_work;
 
diff --git a/fs/io-wq.h b/fs/io-wq.h
index 3c63a99d1629..d5f4e1ae2d5f 100644
--- a/fs/io-wq.h
+++ b/fs/io-wq.h
@@ -96,6 +96,8 @@ typedef void (io_wq_work_fn)(struct io_wq_work *);
 struct io_wq_data {
 	struct user_struct *user;
 
+	unsigned long *hash_map;
+
 	io_wq_work_fn *do_work;
 	free_work_fn *free_work;
 };
diff --git a/fs/io_uring.c b/fs/io_uring.c
index 239eacec3f3a..e71bc4e3bf08 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -359,6 +359,9 @@ struct io_ring_ctx {
 		unsigned		cached_cq_overflow;
 		unsigned long		sq_check_overflow;
 
+		/* hashed buffered write serialization */
+		unsigned long		hash_map;
+
 		struct list_head	defer_list;
 		struct list_head	timeout_list;
 		struct list_head	cq_overflow_list;
@@ -7796,6 +7799,7 @@ static struct io_wq *io_init_wq_offload(struct io_ring_ctx *ctx)
 	unsigned int concurrency;
 
 	data.user = ctx->user;
+	data.hash_map = &ctx->hash_map;
 	data.free_work = io_free_work;
 	data.do_work = io_wq_submit_work;
 
-- 
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