From: Mike Kravetz <mike.kravetz@oracle.com>
To: Rik van Riel <riel@surriel.com>, Michal Hocko <mhocko@kernel.org>,
Roman Gushchin <guro@fb.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Johannes Weiner <hannes@cmpxchg.org>,
linux-mm@kvack.org, kernel-team@fb.com,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] mm: hugetlb: optionally allocate gigantic hugepages using cma
Date: Tue, 10 Mar 2020 13:29:09 -0700 [thread overview]
Message-ID: <c20a0d81-341f-caac-0e47-f8753fbb6dbe@oracle.com> (raw)
In-Reply-To: <4147bc1d429a4336dcb45a6cb2657d082f35ab25.camel@surriel.com>
On 3/10/20 1:15 PM, Rik van Riel wrote:
> On Tue, 2020-03-10 at 13:11 -0700, Mike Kravetz wrote:
>> On 3/10/20 12:46 PM, Rik van Riel wrote:
>>>
>>> How would that work for architectures that have multiple
>>> possible hugetlbfs gigantic page sizes, where the admin
>>> can allocate different numbers of differently sized pages
>>> after bootup?
>>
>> For hugetlb page reservations at boot today, pairs specifying size
>> and
>> quantity are put on the command line. For example,
>> hugepagesz=2M hugepages=512 hugepagesz=1G hugepages=64
>>
>> We could do something similiar for CMA.
>> hugepagesz=512M hugepages_cma=256 hugepagesz=1G hugepages_cma=64
>>
>> That would make things much more complicated (implies separate CMA
>> reservations per size) and may be overkill for the first
>> implementation.
>>
>> Perhaps we limit CMA reservations to one gigantic huge page
>> size. The
>> architectures would need to define the default and there could be a
>> command line option to override. Something like,
>> default_cmapagesz= analogous to today's default_hugepagesz=. Then
>> hugepages_cma= is only associated with that default gigantic huge
>> page
>> size.
>>
>> The more I think about it, the more I like limiting CMA reservations
>> to
>> only one gigantic huge page size (per arch).
>
> Why, though?
>
> The cma_alloc function can return allocations of different
> sizes at the same time.
>
> There is no limitation in the underlying code that would stop
> a user from allocating hugepages of different sizes through
> sysfs.
True, there is no technical reason.
I was only trying to simplify the setup and answer the outstanding questions.
- What alignment to use for reservations?
- What is minimum size of reservations?
If only one gigantic page size is supported, the answer is simple. In any
case, I think input from arch specific code will be needed.
--
Mike Kravetz
> Allowing the system administrator to allocate a little extra
> memory for the CMA pool could also allow us to work around
> initial issues of compaction/migration failing to move some
> of the pages, while we play whack-a-mole with the last corner
> cases.
next prev parent reply other threads:[~2020-03-10 20:30 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-10 0:25 [PATCH v2] mm: hugetlb: optionally allocate gigantic hugepages using cma Roman Gushchin
2020-03-10 0:30 ` Roman Gushchin
2020-03-10 8:45 ` Michal Hocko
2020-03-10 17:25 ` Roman Gushchin
2020-03-10 17:37 ` Michal Hocko
2020-03-16 1:08 ` Rik van Riel
2020-03-10 17:38 ` Mike Kravetz
2020-03-10 17:42 ` Michal Hocko
2020-03-10 9:01 ` Michal Hocko
2020-03-10 17:30 ` Roman Gushchin
2020-03-10 17:39 ` Michal Hocko
2020-03-10 17:58 ` Roman Gushchin
2020-03-10 17:27 ` Mike Kravetz
2020-03-10 18:05 ` Roman Gushchin
2020-03-10 18:22 ` Rik van Riel
2020-03-10 18:33 ` Mike Kravetz
2020-03-10 18:54 ` Andreas Schaufler
2020-03-10 18:56 ` Roman Gushchin
2020-03-10 19:00 ` Andreas Schaufler
2020-03-10 19:19 ` Roman Gushchin
2020-03-10 19:36 ` Michal Hocko
2020-03-10 19:46 ` Rik van Riel
2020-03-10 20:11 ` Mike Kravetz
2020-03-10 20:15 ` Rik van Riel
2020-03-10 20:29 ` Mike Kravetz [this message]
2020-03-10 20:38 ` Rik van Riel
2020-03-10 20:29 ` Roman Gushchin
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