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Message-ID: <c78634ee-0d6f-c98c-3c2a-8cb500c0ae47@oracle.com>
Date: Thu, 15 Oct 2020 16:14:12 -0700
From: Mike Kravetz <mike.kravetz@...cle.com>
To: David Hildenbrand <david@...hat.com>,
Mina Almasry <almasrymina@...gle.com>
Cc: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linux-mm@...ck.org" <linux-mm@...ck.org>,
Michal Privoznik <mprivozn@...hat.com>,
"Michael S. Tsirkin" <mst@...hat.com>,
Michal Hocko <mhocko@...nel.org>,
Muchun Song <songmuchun@...edance.com>,
"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
Tejun Heo <tj@...nel.org>
Subject: Re: cgroup and FALLOC_FL_PUNCH_HOLE: WARNING: CPU: 13 PID: 2438 at
mm/page_counter.c:57 page_counter_uncharge+0x4b/0x5
On 10/14/20 11:31 AM, Mike Kravetz wrote:
> On 10/14/20 11:18 AM, David Hildenbrand wrote:
>
> FWIW - I ran libhugetlbfs tests which do a bunch of hole punching
> with (and without) hugetlb controller enabled and did not see this issue.
>
I took a closer look after running just the fallocate_stress test
in libhugetlbfs. Here are the cgroup counter values:
hugetlb.2MB.failcnt 0
hugetlb.2MB.limit_in_bytes 9223372036854771712
hugetlb.2MB.max_usage_in_bytes 209715200
hugetlb.2MB.rsvd.failcnt 0
hugetlb.2MB.rsvd.limit_in_bytes 9223372036854771712
hugetlb.2MB.rsvd.max_usage_in_bytes 601882624
hugetlb.2MB.rsvd.usage_in_bytes 392167424
hugetlb.2MB.usage_in_bytes 0
We did not hit the WARN_ON_ONCE(), but the 'rsvd.usage_in_bytes' value
is not correct in that it should be zero. No huge page reservations
remain after the test.
HugePages_Total: 1024
HugePages_Free: 1024
HugePages_Rsvd: 0
HugePages_Surp: 0
Hugepagesize: 2048 kB
Hugetlb: 2097152 kB
To try and better understand the reservation cgroup controller, I addded
a few printks to the code. While running fallocate_stress with the
printks, I can consistently hit the WARN_ON_ONCE() due to the counter
going negative. Here are the cgroup counter values after such a run:
hugetlb.2MB.failcnt 0
hugetlb.2MB.limit_in_bytes 9223372036854771712
hugetlb.2MB.max_usage_in_bytes 209715200
hugetlb.2MB.rsvd.failcnt 3
hugetlb.2MB.rsvd.limit_in_bytes 9223372036854771712
hugetlb.2MB.rsvd.max_usage_in_bytes 251658240
hugetlb.2MB.rsvd.usage_in_bytes 18446744073487253504
hugetlb.2MB.usage_in_bytes 0
Again, no reserved pages after the test.
HugePages_Total: 1024
HugePages_Free: 1024
HugePages_Rsvd: 0
HugePages_Surp: 0
Hugepagesize: 2048 kB
Hugetlb: 2097152 kB
I have some basic hugetlb hole punch functionality tests. Running
these on the kernel with added printk's does not cause any issues.
In order to reproduce, I need to run fallocate_stress test which
will cause hole punch to race with page fault. Best guess at this
time is that some of the error/race detection reservation back out
code is not properly dealing with cgroup accounting.
I'll take a look at this as well.
--
Mike Kravetz
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