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From: Mike Kravetz <mike.kravetz@oracle.com>
To: Mina Almasry <almasrymina@google.com>
Cc: shuah@kernel.org, rientjes@google.com, shakeelb@google.com,
	gthelen@google.com, akpm@linux-foundation.org,
	khalid.aziz@oracle.com, linux-kernel@vger.kernel.org,
	linux-mm@kvack.org, linux-kselftest@vger.kernel.org
Subject: Re: [RFC PATCH v2 4/5] hugetlb_cgroup: Add accounting for shared mappings
Date: Wed, 14 Aug 2019 09:46:47 -0700	[thread overview]
Message-ID: <9872cec9-a0fe-cfe0-0df6-90b6dd909f04@oracle.com> (raw)
In-Reply-To: <47cfc50d-bea3-0247-247e-888d2942f134@oracle.com>

On 8/13/19 4:54 PM, Mike Kravetz wrote:
> On 8/8/19 4:13 PM, Mina Almasry wrote:
>> For shared mappings, the pointer to the hugetlb_cgroup to uncharge lives
>> in the resv_map entries, in file_region->reservation_counter.
>>
>> When a file_region entry is added to the resv_map via region_add, we
>> also charge the appropriate hugetlb_cgroup and put the pointer to that
>> in file_region->reservation_counter. This is slightly delicate since we
>> need to not modify the resv_map until we know that charging the
>> reservation has succeeded. If charging doesn't succeed, we report the
>> error to the caller, so that the kernel fails the reservation.
> 
> I wish we did not need to modify these region_() routines as they are
> already difficult to understand.  However, I see no other way with the
> desired semantics.
> 

I suspect you have considered this, but what about using the return value
from region_chg() in hugetlb_reserve_pages() to charge reservation limits?
There is a VERY SMALL race where the value could be too large, but that
can be checked and adjusted at region_add time as is done with normal
accounting today.  If the question is, where would we store the information
to uncharge?, then we can hang a structure off the vma.  This would be
similar to what is done for private mappings.  In fact, I would suggest
making them both use a new cgroup reserve structure hanging off the vma.

One issue I see is what to do if a vma is split?  The private mapping case
'should' handle this today, but I would not be surprised if such code is
missing or incorrect.

-- 
Mike Kravetz

  reply	other threads:[~2019-08-14 16:46 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-08 23:13 [RFC PATCH v2 0/5] hugetlb_cgroup: Add hugetlb_cgroup reservation limits Mina Almasry
2019-08-08 23:13 ` [RFC PATCH v2 1/5] hugetlb_cgroup: Add hugetlb_cgroup reservation counter Mina Almasry
2019-08-08 23:13 ` [RFC PATCH v2 2/5] hugetlb_cgroup: Add interface for charge/uncharge Mina Almasry
2019-08-08 23:13 ` [RFC PATCH v2 3/5] hugetlb_cgroup: Add reservation accounting for private mappings Mina Almasry
2019-08-08 23:13 ` [RFC PATCH v2 4/5] hugetlb_cgroup: Add accounting for shared mappings Mina Almasry
2019-08-13 23:54   ` Mike Kravetz
2019-08-14 16:46     ` Mike Kravetz [this message]
2019-08-15 23:04       ` Mina Almasry
2019-08-16 16:28         ` Mike Kravetz
2019-08-16 18:06           ` Mina Almasry
2019-08-15 23:08     ` Mina Almasry
2019-08-16 16:33       ` Mike Kravetz
2019-08-08 23:13 ` [RFC PATCH v2 5/5] hugetlb_cgroup: Add hugetlb_cgroup reservation tests Mina Almasry
2019-08-09 17:54 ` [RFC PATCH v2 0/5] hugetlb_cgroup: Add hugetlb_cgroup reservation limits Mike Kravetz
2019-08-09 19:42   ` Mina Almasry
2019-08-10 18:58     ` Mike Kravetz
2019-08-10 22:01       ` Mina Almasry
2019-08-13 23:40         ` Mike Kravetz
     [not found] ` <20190815035352.14952-1-hdanton@sina.com>
2019-08-15 23:21   ` [RFC PATCH v2 1/5] hugetlb_cgroup: Add hugetlb_cgroup reservation counter Mina Almasry

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