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From:   Yafang Shao <laoar.shao@gmail.com>
To:     hannes@cmpxchg.org, peterz@infradead.org, akpm@linux-foundation.org
Cc:     linux-mm@kvack.org, linux-block@vger.kernel.org,
        linux-kernel@vger.kernel.org, Yafang Shao <laoar.shao@gmail.com>
Subject: [PATCH v2 1/2] psi: introduce various types of memstall
Date:   Tue, 31 Mar 2020 06:04:36 -0400
Message-Id: <1585649077-10896-2-git-send-email-laoar.shao@gmail.com>
In-Reply-To: <1585649077-10896-1-git-send-email-laoar.shao@gmail.com>
References: <1585649077-10896-1-git-send-email-laoar.shao@gmail.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

The memstall is used as a memory pressure index now. But there're many
paths to get into memstall, so once memstall happens we don't know the
specific reason of it.

This patch introduces various types of memstall as bellow,
	MEMSTALL_KSWAPD
	MEMSTALL_RECLAIM_DIRECT
	MEMSTALL_RECLAIM_MEMCG
	MEMSTALL_RECLAIM_HIGH
	MEMSTALL_KCOMPACTD
	MEMSTALL_COMPACT
	MEMSTALL_WORKINGSET_REFAULT
	MEMSTALL_WORKINGSET_THRASH
	MEMSTALL_MEMDELAY
	MEMSTALL_SWAPIO
and adds a new parameter 'type' in psi_memstall_{enter, leave}.

After that, we can trace specific types of memstall with other
powerful tools like tracepoint, kprobe, ebpf and etc. It can also help us
to analyze latency spike caused by memory pressure. But note that we
can't use it to build memory pressure for a specific type of memstall,
e.g. memcg pressure, compaction pressure and etc, because it doesn't
implement various types of task->in_memstall, e.g. task->in_memcgstall,
task->in_compactionstall and etc. IOW, the main goal of it is to trace
the spread of latencies and the specific reason of these latencies.

Although there're already some tracepoints can help us to achieve this
goal, e.g.
	vmscan:mm_vmscan_kswapd_{wake, sleep}
	vmscan:mm_vmscan_direct_reclaim_{begin, end}
	vmscan:mm_vmscan_memcg_reclaim_{begin, end}
	/* no tracepoint for memcg high reclaim*/
	compcation:mm_compaction_kcompactd_{wake, sleep}
	compcation:mm_compaction_begin_{begin, end}
	/* no tracepoint for workingset refault */
	/* no tracepoint for workingset thrashing */
	/* no tracepoint for use memdelay */
	/* no tracepoint for swapio */
but psi_memstall_{enter, leave} gives us a unified entrance for all
types of memstall and we don't need to add many begin and end tracepoints
that hasn't been implemented yet.

Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
---
 block/blk-cgroup.c        |  4 ++--
 block/blk-core.c          |  4 ++--
 include/linux/psi.h       | 15 +++++++++++----
 include/linux/psi_types.h | 13 +++++++++++++
 kernel/sched/psi.c        |  6 ++++--
 mm/compaction.c           |  4 ++--
 mm/filemap.c              |  4 ++--
 mm/memcontrol.c           |  4 ++--
 mm/page_alloc.c           |  8 ++++----
 mm/page_io.c              |  4 ++--
 mm/vmscan.c               |  8 ++++----
 11 files changed, 48 insertions(+), 26 deletions(-)

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index a229b94d5390..fc24095c13c0 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -1593,7 +1593,7 @@ static void blkcg_maybe_throttle_blkg(struct blkcg_gq *blkg, bool use_memdelay)
 	delay_nsec = min_t(u64, delay_nsec, 250 * NSEC_PER_MSEC);
 
 	if (use_memdelay)
-		psi_memstall_enter(&pflags);
+		psi_memstall_enter(&pflags, MEMSTALL_MEMDELAY);
 
 	exp = ktime_add_ns(now, delay_nsec);
 	tok = io_schedule_prepare();
@@ -1605,7 +1605,7 @@ static void blkcg_maybe_throttle_blkg(struct blkcg_gq *blkg, bool use_memdelay)
 	io_schedule_finish(tok);
 
 	if (use_memdelay)
-		psi_memstall_leave(&pflags);
+		psi_memstall_leave(&pflags, MEMSTALL_MEMDELAY);
 }
 
 /**
diff --git a/block/blk-core.c b/block/blk-core.c
index 60dc9552ef8d..e2039cf4719a 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1190,12 +1190,12 @@ blk_qc_t submit_bio(struct bio *bio)
 	 * submission can be a significant part of overall IO time.
 	 */
 	if (workingset_read)
-		psi_memstall_enter(&pflags);
+		psi_memstall_enter(&pflags, MEMSTALL_WORKINGSET_REFAULT);
 
 	ret = generic_make_request(bio);
 
 	if (workingset_read)
-		psi_memstall_leave(&pflags);
+		psi_memstall_leave(&pflags, MEMSTALL_WORKINGSET_REFAULT);
 
 	return ret;
 }
diff --git a/include/linux/psi.h b/include/linux/psi.h
index 7b3de7321219..7bf94f6fb5e8 100644
--- a/include/linux/psi.h
+++ b/include/linux/psi.h
@@ -19,8 +19,8 @@ void psi_init(void);
 void psi_task_change(struct task_struct *task, int clear, int set);
 
 void psi_memstall_tick(struct task_struct *task, int cpu);
-void psi_memstall_enter(unsigned long *flags);
-void psi_memstall_leave(unsigned long *flags);
+void psi_memstall_enter(unsigned long *flags, enum memstall_types type);
+void psi_memstall_leave(unsigned long *flags, enum memstall_types type);
 
 int psi_show(struct seq_file *s, struct psi_group *group, enum psi_res res);
 
@@ -41,8 +41,15 @@ __poll_t psi_trigger_poll(void **trigger_ptr, struct file *file,
 
 static inline void psi_init(void) {}
 
-static inline void psi_memstall_enter(unsigned long *flags) {}
-static inline void psi_memstall_leave(unsigned long *flags) {}
+static inline void psi_memstall_enter(unsigned long *flags,
+				      enum memstall_types type)
+{
+}
+
+static inline void psi_memstall_leave(unsigned long *flags,
+				      enum memstall_types type)
+{
+}
 
 #ifdef CONFIG_CGROUPS
 static inline int psi_cgroup_alloc(struct cgroup *cgrp)
diff --git a/include/linux/psi_types.h b/include/linux/psi_types.h
index 07aaf9b82241..48ebb51484f9 100644
--- a/include/linux/psi_types.h
+++ b/include/linux/psi_types.h
@@ -7,6 +7,19 @@
 #include <linux/kref.h>
 #include <linux/wait.h>
 
+enum memstall_types {
+	MEMSTALL_KSWAPD,
+	MEMSTALL_RECLAIM_DIRECT,
+	MEMSTALL_RECLAIM_MEMCG,
+	MEMSTALL_RECLAIM_HIGH,
+	MEMSTALL_KCOMPACTD,
+	MEMSTALL_COMPACT,
+	MEMSTALL_WORKINGSET_REFAULT,
+	MEMSTALL_WORKINGSET_THRASH,
+	MEMSTALL_MEMDELAY,
+	MEMSTALL_SWAPIO,
+};
+
 #ifdef CONFIG_PSI
 
 /* Tracked task states */
diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
index 028520702717..460f08436b58 100644
--- a/kernel/sched/psi.c
+++ b/kernel/sched/psi.c
@@ -806,11 +806,12 @@ void psi_memstall_tick(struct task_struct *task, int cpu)
 /**
  * psi_memstall_enter - mark the beginning of a memory stall section
  * @flags: flags to handle nested sections
+ * @type: type of memstall
  *
  * Marks the calling task as being stalled due to a lack of memory,
  * such as waiting for a refault or performing reclaim.
  */
-void psi_memstall_enter(unsigned long *flags)
+void psi_memstall_enter(unsigned long *flags, enum memstall_types type)
 {
 	struct rq_flags rf;
 	struct rq *rq;
@@ -837,10 +838,11 @@ void psi_memstall_enter(unsigned long *flags)
 /**
  * psi_memstall_leave - mark the end of an memory stall section
  * @flags: flags to handle nested memdelay sections
+ * @type: type of memstall
  *
  * Marks the calling task as no longer stalled due to lack of memory.
  */
-void psi_memstall_leave(unsigned long *flags)
+void psi_memstall_leave(unsigned long *flags, enum memstall_types type)
 {
 	struct rq_flags rf;
 	struct rq *rq;
diff --git a/mm/compaction.c b/mm/compaction.c
index 672d3c78c6ab..c0d533192974 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -2647,9 +2647,9 @@ static int kcompactd(void *p)
 		wait_event_freezable(pgdat->kcompactd_wait,
 				kcompactd_work_requested(pgdat));
 
-		psi_memstall_enter(&pflags);
+		psi_memstall_enter(&pflags, MEMSTALL_KCOMPACTD);
 		kcompactd_do_work(pgdat);
-		psi_memstall_leave(&pflags);
+		psi_memstall_leave(&pflags, MEMSTALL_KCOMPACTD);
 	}
 
 	return 0;
diff --git a/mm/filemap.c b/mm/filemap.c
index 1784478270e1..f5459e3850ef 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1123,7 +1123,7 @@ static inline int wait_on_page_bit_common(wait_queue_head_t *q,
 			delayacct_thrashing_start();
 			delayacct = true;
 		}
-		psi_memstall_enter(&pflags);
+		psi_memstall_enter(&pflags, MEMSTALL_WORKINGSET_THRASH);
 		thrashing = true;
 	}
 
@@ -1182,7 +1182,7 @@ static inline int wait_on_page_bit_common(wait_queue_head_t *q,
 	if (thrashing) {
 		if (delayacct)
 			delayacct_thrashing_end();
-		psi_memstall_leave(&pflags);
+		psi_memstall_leave(&pflags, MEMSTALL_WORKINGSET_THRASH);
 	}
 
 	/*
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 7a4bd8b9adc2..a9b336ea7fe5 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2399,9 +2399,9 @@ void mem_cgroup_handle_over_high(void)
 	 * schedule_timeout_killable sets TASK_KILLABLE). This means we don't
 	 * need to account for any ill-begotten jiffies to pay them off later.
 	 */
-	psi_memstall_enter(&pflags);
+	psi_memstall_enter(&pflags, MEMSTALL_RECLAIM_HIGH);
 	schedule_timeout_killable(penalty_jiffies);
-	psi_memstall_leave(&pflags);
+	psi_memstall_leave(&pflags, MEMSTALL_RECLAIM_HIGH);
 
 out:
 	css_put(&memcg->css);
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 3c4eb750a199..8789234a2fca 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3884,14 +3884,14 @@ __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order,
 	if (!order)
 		return NULL;
 
-	psi_memstall_enter(&pflags);
+	psi_memstall_enter(&pflags, MEMSTALL_COMPACT);
 	noreclaim_flag = memalloc_noreclaim_save();
 
 	*compact_result = try_to_compact_pages(gfp_mask, order, alloc_flags, ac,
 								prio, &page);
 
 	memalloc_noreclaim_restore(noreclaim_flag);
-	psi_memstall_leave(&pflags);
+	psi_memstall_leave(&pflags, MEMSTALL_COMPACT);
 
 	/*
 	 * At least in one zone compaction wasn't deferred or skipped, so let's
@@ -4106,7 +4106,7 @@ __perform_reclaim(gfp_t gfp_mask, unsigned int order,
 
 	/* We now go into synchronous reclaim */
 	cpuset_memory_pressure_bump();
-	psi_memstall_enter(&pflags);
+	psi_memstall_enter(&pflags, MEMSTALL_RECLAIM_DIRECT);
 	fs_reclaim_acquire(gfp_mask);
 	noreclaim_flag = memalloc_noreclaim_save();
 
@@ -4115,7 +4115,7 @@ __perform_reclaim(gfp_t gfp_mask, unsigned int order,
 
 	memalloc_noreclaim_restore(noreclaim_flag);
 	fs_reclaim_release(gfp_mask);
-	psi_memstall_leave(&pflags);
+	psi_memstall_leave(&pflags, MEMSTALL_RECLAIM_DIRECT);
 
 	cond_resched();
 
diff --git a/mm/page_io.c b/mm/page_io.c
index 76965be1d40e..67de6b1801a4 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -369,7 +369,7 @@ int swap_readpage(struct page *page, bool synchronous)
 	 * or the submitting cgroup IO-throttled, submission can be a
 	 * significant part of overall IO time.
 	 */
-	psi_memstall_enter(&pflags);
+	psi_memstall_enter(&pflags, MEMSTALL_SWAPIO);
 
 	if (frontswap_load(page) == 0) {
 		SetPageUptodate(page);
@@ -431,7 +431,7 @@ int swap_readpage(struct page *page, bool synchronous)
 	bio_put(bio);
 
 out:
-	psi_memstall_leave(&pflags);
+	psi_memstall_leave(&pflags, MEMSTALL_SWAPIO);
 	return ret;
 }
 
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 876370565455..4445c1dd9551 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -3352,13 +3352,13 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
 
 	trace_mm_vmscan_memcg_reclaim_begin(0, sc.gfp_mask);
 
-	psi_memstall_enter(&pflags);
+	psi_memstall_enter(&pflags, MEMSTALL_RECLAIM_MEMCG);
 	noreclaim_flag = memalloc_noreclaim_save();
 
 	nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
 
 	memalloc_noreclaim_restore(noreclaim_flag);
-	psi_memstall_leave(&pflags);
+	psi_memstall_leave(&pflags, MEMSTALL_RECLAIM_MEMCG);
 
 	trace_mm_vmscan_memcg_reclaim_end(nr_reclaimed);
 	set_task_reclaim_state(current, NULL);
@@ -3568,7 +3568,7 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx)
 	};
 
 	set_task_reclaim_state(current, &sc.reclaim_state);
-	psi_memstall_enter(&pflags);
+	psi_memstall_enter(&pflags, MEMSTALL_KSWAPD);
 	__fs_reclaim_acquire();
 
 	count_vm_event(PAGEOUTRUN);
@@ -3747,7 +3747,7 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx)
 
 	snapshot_refaults(NULL, pgdat);
 	__fs_reclaim_release();
-	psi_memstall_leave(&pflags);
+	psi_memstall_leave(&pflags, MEMSTALL_KSWAPD);
 	set_task_reclaim_state(current, NULL);
 
 	/*
-- 
2.18.2