Re: [PATCH v7 00/10] per lruvec lru_lock for memcg

I tried with the mods you had appended, from [PATCH v7 02/10]
discussion with Konstantion: no, still crashes in a similar way.> 
Does your github tree have other changes too?  I see it says "Latest
commit e05d0dd 22 days ago", which doesn't seem to fit.  Afraid I
don't have time to test many variations.

Thanks a lot for testing! the github version is same as your tested.
The github branches page has a bug, it don't show correct update time.
https://github.com/alexshi/linux/branches while detailed page does. 
https://github.com/alexshi/linux/tree/lru-next 

It looks like, in my case, systemd was usually jumping in and doing
something with shmem (perhaps via memfd) that read back from swap
and triggered the crash without any further intervention from me.

So please try booting with mem=700M and 1.5G swap,
mount -t tmpfs -o size=470M tmpfs /tst
cp /dev/zero /tst; cp /tst/zero /dev/null

That's enough to crash it for me, without getting into any losetup or
systemd complications. But you might have to adjust the numbers to be
sure of writing out and reading back from swap.

It's swap to SSD in my case, don't think that matters. I happen to
run with swappiness 100 (precisely to help generate swap problems),
but swappiness 60 is good enough to get these crashes.

I did use 700M memory and 1.5G swapfile in my qemu, but with a swapfile
not a disk.
qemu-system-x86_64  -smp 4 -enable-kvm -cpu SandyBridge \
	-m 700M -kernel /home/kuiliang.as/linux/qemulru/arch/x86/boot/bzImage \
	-append "earlyprintk=ttyS0 root=/dev/sda1 console=ttyS0 debug crashkernel=128M printk.devkmsg=on " \
	-hda /home/kuiliang.as/rootimages/CentOS-7-x86_64-Azure-1703.qcow2 \
	-hdb /home/kuiliang.as/rootimages/hdb.qcow2 \
	--nographic \

Anyway, although I didn't reproduced the bug. but I found a bug in my
debug function:
	VM_BUG_ON_PAGE(lruvec_memcg(lruvec) != page->mem_cgroup, page);

 if !page->mem_cgroup, the bug could be triggered, so, seems it's a bug
for debug function, not real issue. The 9th patch should be replaced by
the following new patch. 

Many thanks for testing!
Alex

From ac6d3e2bcfba5727d5c03f9655bb0c7443f655eb Mon Sep 17 00:00:00 2001
From: Alex Shi <redacted>
Date: Mon, 23 Dec 2019 13:33:54 +0800
Subject: [PATCH v8 8/9] mm/lru: add debug checking for page memcg moving

This debug patch could give some clues if there are sth out of
consideration.

Signed-off-by: Alex Shi <redacted>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Vladimir Davydov <redacted>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: cgroups@vger.kernel.org
Cc: linux-mm@kvack.org
Cc: linux-kernel@vger.kernel.org
---
 include/linux/memcontrol.h |  5 +++++
 mm/compaction.c            |  2 ++
 mm/memcontrol.c            | 13 +++++++++++++
 3 files changed, 20 insertions(+)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 09e861df48e8..ece88bb11d0f 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h

@@ -421,6 +421,7 @@ struct lruvec *lock_page_lruvec_irq(struct page *);
 struct lruvec *lock_page_lruvec_irqsave(struct page *, unsigned long*);
 void unlock_page_lruvec_irq(struct lruvec *);
 void unlock_page_lruvec_irqrestore(struct lruvec *, unsigned long);
+void lruvec_memcg_debug(struct lruvec *lruvec, struct page *page);
 
 struct mem_cgroup *mem_cgroup_from_task(struct task_struct *p);
 

@@ -1183,6 +1184,10 @@ static inline
 void count_memcg_event_mm(struct mm_struct *mm, enum vm_event_item idx)
 {
 }
+
+static inline void lruvec_memcg_debug(struct lruvec *lruvec, struct page *page)
+{
+}
 #endif /* CONFIG_MEMCG */
 
 /* idx can be of type enum memcg_stat_item or node_stat_item */

diff --git a/mm/compaction.c b/mm/compaction.c
index 8c0a2da217d8..151242817bf4 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c

@@ -971,6 +971,8 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
 			compact_lock_irqsave(&lruvec->lru_lock, &flags, cc);
 			locked_lruvec = lruvec;
 
+			lruvec_memcg_debug(lruvec, page);
+
 			/* Try get exclusive access under lock */
 			if (!skip_updated) {
 				skip_updated = true;

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 00fef8ddbd08..a473da8d2275 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c

@@ -1238,6 +1238,17 @@ struct lruvec *mem_cgroup_page_lruvec(struct page *page, struct pglist_data *pgd
 	return lruvec;
 }
 
+void lruvec_memcg_debug(struct lruvec *lruvec, struct page *page)
+{
+	if (mem_cgroup_disabled())
+		return;
+
+	if (!page->mem_cgroup)
+		VM_BUG_ON_PAGE(lruvec_memcg(lruvec) != root_mem_cgroup, page);
+	else
+		VM_BUG_ON_PAGE(lruvec_memcg(lruvec) != page->mem_cgroup, page);
+}
+
 struct lruvec *lock_page_lruvec_irq(struct page *page)
 {
 	struct lruvec *lruvec;

@@ -1247,6 +1258,7 @@ struct lruvec *lock_page_lruvec_irq(struct page *page)
 	lruvec = mem_cgroup_lruvec(memcg, page_pgdat(page));
 	spin_lock_irq(&lruvec->lru_lock);
 
+	lruvec_memcg_debug(lruvec, page);
 	return lruvec;
 }
 

@@ -1259,6 +1271,7 @@ struct lruvec *lock_page_lruvec_irqsave(struct page *page, unsigned long *flags)
 	lruvec = mem_cgroup_lruvec(memcg, page_pgdat(page));
 	spin_lock_irqsave(&lruvec->lru_lock, *flags);
 
+	lruvec_memcg_debug(lruvec, page);
 	return lruvec;
 }
 

-- 
2.22.0