linux-kernel - Re: [PATCH v3] mm, oom: make the calculation of oom badness more accurate

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Date:   Mon, 13 Jul 2020 12:39:39 +1000
From:   Stephen Rothwell <sfr@...b.auug.org.au>
To:     Yafang Shao <laoar.shao@...il.com>
Cc:     mhocko@...nel.org, cai@....pw, rientjes@...gle.com,
        akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-next@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] mm, oom: make the calculation of oom badness more
 accurate

Hi all,

On Fri, 10 Jul 2020 11:57:31 -0400 Yafang Shao <laoar.shao@...il.com> wrote:
>
> ---
> v2 -> v3:
> - fix the type of variable 'point' in oom_evaluate_task()
> - initialize oom_control->chosen_points in select_bad_process() per Michal
> - update the comment in proc_oom_score() per Michal

I have applied the following incremental patch to linux-next today.

From: Stephen Rothwell <sfr@...b.auug.org.au>
Date: Mon, 13 Jul 2020 12:34:46 +1000
Subject: [PATCH] mm-oom-make-the-calculation-of-oom-badness-more-accurate-fix

Signed-off-by: Stephen Rothwell <sfr@...b.auug.org.au>
---
 drivers/tty/sysrq.c |  1 -
 fs/proc/base.c      | 10 +++++++---
 mm/memcontrol.c     |  1 -
 mm/oom_kill.c       |  5 +++--
 mm/page_alloc.c     |  1 -
 5 files changed, 10 insertions(+), 8 deletions(-)

diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c
index e83fd46f632c..7c95afa905a0 100644
--- a/drivers/tty/sysrq.c
+++ b/drivers/tty/sysrq.c
@@ -382,7 +382,6 @@ static void moom_callback(struct work_struct *ignored)
 		.memcg = NULL,
 		.gfp_mask = gfp_mask,
 		.order = -1,
-		.chosen_points = LONG_MIN,
 	};
 
 	mutex_lock(&oom_lock);
diff --git a/fs/proc/base.c b/fs/proc/base.c
index bf164064b901..10c2a26c0e20 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -554,10 +554,14 @@ static int proc_oom_score(struct seq_file *m, struct pid_namespace *ns,
 	long badness;
 
 	badness = oom_badness(task, totalpages);
-	if (badness != LONG_MIN) {
-		/* Let's keep the range of points as [0, 2000]. */
+	/*
+	 * Special case OOM_SCORE_ADJ_MIN for all others scale the
+	 * badness value into [0, 2000] range which we have been
+	 * exporting for a long time so userspace might depend on it.
+	 */
+	if (badness != LONG_MIN)
 		points = (1000 + badness * 1000 / (long)totalpages) * 2 / 3;
-	}
+
 	seq_printf(m, "%lu\n", points);
 
 	return 0;
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 4ae64726f863..430d4c659669 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1666,7 +1666,6 @@ static bool mem_cgroup_out_of_memory(struct mem_cgroup *memcg, gfp_t gfp_mask,
 		.memcg = memcg,
 		.gfp_mask = gfp_mask,
 		.order = order,
-		.chosen_points = LONG_MIN,
 	};
 	bool ret;
 
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 8fdb8b03f5cd..48e0db54d838 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -306,7 +306,7 @@ static enum oom_constraint constrained_alloc(struct oom_control *oc)
 static int oom_evaluate_task(struct task_struct *task, void *arg)
 {
 	struct oom_control *oc = arg;
-	unsigned long points;
+	long points;
 
 	if (oom_unkillable_task(task))
 		goto next;
@@ -361,6 +361,8 @@ static int oom_evaluate_task(struct task_struct *task, void *arg)
  */
 static void select_bad_process(struct oom_control *oc)
 {
+	oc->chosen_points = LONG_MIN;
+
 	if (is_memcg_oom(oc))
 		mem_cgroup_scan_tasks(oc->memcg, oom_evaluate_task, oc);
 	else {
@@ -1124,7 +1126,6 @@ void pagefault_out_of_memory(void)
 		.memcg = NULL,
 		.gfp_mask = 0,
 		.order = 0,
-		.chosen_points = LONG_MIN,
 	};
 
 	if (mem_cgroup_oom_synchronize(true))
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 0832b21a7728..65fc0ed784d2 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3915,7 +3915,6 @@ __alloc_pages_may_oom(gfp_t gfp_mask, unsigned int order,
 		.memcg = NULL,
 		.gfp_mask = gfp_mask,
 		.order = order,
-		.chosen_points = LONG_MIN,
 	};
 	struct page *page;
 
-- 
2.27.0

-- 
Cheers,
Stephen Rothwell

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