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From: Mike Kravetz <mike.kravetz@oracle.com>
To: Mina Almasry <almasrymina@google.com>
Cc: shuah <shuah@kernel.org>, "David Rientjes" <rientjes@google.com>,
	"Shakeel Butt" <shakeelb@google.com>,
	"Greg Thelen" <gthelen@google.com>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	"open list" <linux-kernel@vger.kernel.org>,
	linux-mm@kvack.org, linux-kselftest@vger.kernel.org,
	cgroups@vger.kernel.org,
	"Aneesh Kumar" <aneesh.kumar@linux.vnet.ibm.com>,
	"Michal Koutný" <mkoutny@suse.com>,
	"Hillf Danton" <hdanton@sina.com>
Subject: Re: [PATCH v9 1/8] hugetlb_cgroup: Add hugetlb_cgroup reservation counter
Date: Mon, 13 Jan 2020 14:05:58 -0800
Message-ID: <a78595a8-448c-14bb-a54b-9be685f36388@oracle.com> (raw)
In-Reply-To: <CAHS8izNs24KOaRuQkVUuZZUh42rvkyBXJEJYrHNf9bLFnZEXCg@mail.gmail.com>

On 1/13/20 1:03 PM, Mina Almasry wrote:
> On Mon, Jan 13, 2020 at 10:44 AM Mike Kravetz <mike.kravetz@oracle.com> wrote:
>>
>> On 12/17/19 3:16 PM, Mina Almasry wrote:
>>> - While usage_in_bytes tracks all *faulted* hugetlb memory,
>>> reservation_usage_in_bytes tracks all *reserved* hugetlb memory and
>>> hugetlb memory faulted in without a prior reservation.
>>
>> To me, this implies that 'faults without reservations' could cause
>> reservation usage to exceed reservation limit?  Or, does the faulting
>> process get a SIGBUS because of the reservation limit even though it
>> is not using reservations?
>>
>> We shall see in subsequent patches.
>>
> 
> The design we went with based on previous discussions is as follows:
> hugetlb pages faulted without a prior reservation get accounted at
> fault time, rather than reservation time, and if the fault causes the
> counter to cross the limit, the charge fails, hence the fault fails,
> hence the process gets sigbus'd.

Ok, sorry I did not recall the design discussion.

> This means that one counter I'm adding here can cover both use cases:
> if the userspace uses MAP_NORESERVE, then their memory is accounted at
> fault time and they may get sigbus'd.

Let's make sure this is clearly documented.  Someone could be surprised
if their application not using reserves gets a SIGBUS because there is a
reserve limit.
-- 
Mike Kravetz

  reply index

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-12-17 23:16 Mina Almasry
2019-12-17 23:16 ` [PATCH v9 2/8] hugetlb_cgroup: add interface for charge/uncharge hugetlb reservations Mina Almasry
2020-01-13 22:14   ` Mike Kravetz
2020-01-14  0:45     ` David Rientjes
2020-01-14 22:55     ` Mina Almasry
2019-12-17 23:16 ` [PATCH v9 3/8] hugetlb_cgroup: add reservation accounting for private mappings Mina Almasry
2020-01-14  0:55   ` Mike Kravetz
2020-01-14 22:52     ` Mina Almasry
2020-01-17 22:09       ` Mike Kravetz
2020-01-22 21:40         ` Mina Almasry
2019-12-17 23:16 ` [PATCH v9 4/8] hugetlb: disable region_add file_region coalescing Mina Almasry
2020-01-21 17:38   ` Mike Kravetz
2020-01-21 17:40     ` Mike Kravetz
2019-12-17 23:16 ` [PATCH v9 5/8] hugetlb_cgroup: add accounting for shared mappings Mina Almasry
2019-12-17 23:16 ` [PATCH v9 6/8] hugetlb_cgroup: support noreserve mappings Mina Almasry
2020-01-14  0:48   ` David Rientjes
2019-12-17 23:16 ` [PATCH v9 7/8] hugetlb_cgroup: Add hugetlb_cgroup reservation tests Mina Almasry
2019-12-17 23:16 ` [PATCH v9 8/8] hugetlb_cgroup: Add hugetlb_cgroup reservation docs Mina Almasry
2020-01-14  0:54   ` David Rientjes
2019-12-19  1:12 ` [PATCH v9 1/8] hugetlb_cgroup: Add hugetlb_cgroup reservation counter Andrew Morton
2019-12-19  1:37   ` Mike Kravetz
2019-12-19  1:59     ` Mina Almasry
2020-01-13 18:43 ` Mike Kravetz
2020-01-13 21:03   ` Mina Almasry
2020-01-13 22:05     ` Mike Kravetz [this message]
2020-01-13 22:21       ` Mina Almasry
2020-01-14  0:45 ` David Rientjes

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