From: Mike Kravetz <mike.kravetz@oracle.com>
To: Michal Hocko <mhocko@kernel.org>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Matthew Wilcox <willy@infradead.org>,
akpm@linux-foundation.org, ak@linux.intel.com,
mtk.manpages@gmail.com, Davidlohr Bueso <dbueso@suse.de>,
khandual@linux.vnet.ibm.com, aneesh.kumar@linux.vnet.ibm.com,
aarcange@redhat.com
Subject: Re: [RFC PATCH 3/3] mm: shm: Use new hugetlb size encoding definitions
Date: Thu, 27 Jul 2017 14:18:11 -0700 [thread overview]
Message-ID: <9baf7efb-3772-b101-b68a-ab88c02bfc40@oracle.com> (raw)
In-Reply-To: <20170727075051.GJ20970@dhcp22.suse.cz>
On 07/27/2017 12:50 AM, Michal Hocko wrote:
> On Wed 26-07-17 10:39:30, Mike Kravetz wrote:
>> On 07/26/2017 03:07 AM, Michal Hocko wrote:
>>> On Wed 26-07-17 11:53:38, Michal Hocko wrote:
>>>> On Mon 17-07-17 15:28:01, Mike Kravetz wrote:
>>>>> Use the common definitions from hugetlb_encode.h header file for
>>>>> encoding hugetlb size definitions in shmget system call flags. In
>>>>> addition, move these definitions to the from the internal to user
>>>>> (uapi) header file.
>>>>
>>>> s@to the from@from@
>>>>
>>>>>
>>>>> Suggested-by: Matthew Wilcox <willy@infradead.org>
>>>>> Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
>>>>
>>>> with s@HUGETLB_FLAG_ENCODE__16GB@HUGETLB_FLAG_ENCODE_16GB@
>>>>
>>>> Acked-by: Michal Hocko <mhocko@suse.com>
>>>
>>> Btw. man page mentions only 2MB and 1GB, we should document others and
>>> note that each arch might support only subset of them
>>
>> Thanks for looking at these Michal.
>> BTW, those definitions below are wrong. They should be SHM_HUGE_*. :(
>
> Ups, and I completely missed that.
>
>> In the overview of this RFC, I mentioned still needing to address the
>> comment from Aneesh about splitting SHM_HUGE_* definitions into arch
>> specific header files. This is how it is done for mmap. If an arch
>> supports multiple huge page sizes, the 'asm/mman.h' contains definitions
>> for those sizes. There will be a bit of churn (such as header file
>> renaming) to do this for shm as well. So, I keep going back and forth
>> asking myself 'is it worth it'?
>
> Why cannot we use a generic header? Btw. I think it would be better for
> MMAP definitions as well.
I assume you are asking about a uapi asm-generic header file? Currently
mmap has two such files: mman.h and mman-common.h. In order to get the
definitions in such files, arch specific header files must #include the
asm-generic headers. There are arch specific mmap headers today that do
not include either of the asm-generic headers. And, they have their own
definitions for MAP_HUGE_SHIFT. So, it seems we can not use one of the
existing mmap asm-generic header files. Rather, we would need to create
a new one and have that included by all arch specific files.
However, ALL the MAP_HUGE_* definitions in all the arch specific and
asm-generic header files are the same. It would be possible to just put
all those MAP_HUGE_* definitions in the primary uapi header file
(include/uapi/linux/mman.h). If there was ever a need for arch specific
values in the future, we could split them out at that time.
>> Some things to consider.
>>
>> - We should be consistent between mmap and shm. Also remember, that I
>> will propose adding the same type of encoding to memfd_create. So,
>> three system calls will use the encoding. They should be consistent.
>
> agreed
>
>> - Adding the arch specific definitions seems the 'most correct', as a
>> user can not use a definition not supported by the arch. However,
>> even if an arch supports a huge page size it does not mean that the
>> running kernel supports that size. Therefore, the folllowing is in
>> the man page.
>> "The range of huge page sizes that are supported by the system
>> can be discovered by listing the subdirectories in
>> /sys/kernel/mm/hugepages."
>
> Doesn't the respective call return -EINVAL on the unsupported hugepage
> size?
Yes, it does.
>> - Another alternative is to make all known huge page sizes available
>> to all users. This is 'easier' as the definitions can likely reside
>> in a common header file. The user will need to determine what
>> huge page sizes are supported by the running kernel as mentioned in
>> the man page.
>
> yes I think this makes more sense.
Ok, thanks.
The only remaining question is what kind of common header to use:
1) An asm-generic header file in case there may be arch specific differences
in the future.
2) Use the primary uapi header file in include/uapi/linux/mman|shm.h.
--
Mike Kravetz
next prev parent reply other threads:[~2017-07-27 21:19 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-03-08 17:06 [PATCH] mm,hugetlb: compute page_size_log properly Davidlohr Bueso
2017-03-08 19:39 ` Andi Kleen
2017-03-09 3:24 ` Anshuman Khandual
2017-03-09 8:55 ` Michal Hocko
2017-03-28 16:53 ` Davidlohr Bueso
2017-03-28 16:55 ` Davidlohr Bueso
2017-03-28 17:54 ` Matthew Wilcox
2017-03-29 8:06 ` Michal Hocko
2017-03-29 17:45 ` Andi Kleen
2017-03-30 6:12 ` Michal Hocko
2017-04-12 16:18 ` Davidlohr Bueso
2017-04-12 16:30 ` Andi Kleen
2017-04-12 17:21 ` Matthew Wilcox
2017-04-13 6:02 ` Aneesh Kumar K.V
2017-04-13 12:46 ` Matthew Wilcox
2017-07-17 22:27 ` Mike Kravetz
2017-07-17 22:27 ` [RFC PATCH 1/3] mm:hugetlb: Define system call hugetlb size encodings in single file Mike Kravetz
2017-07-18 0:00 ` Matthew Wilcox
2017-07-26 9:50 ` Michal Hocko
2017-07-17 22:28 ` [RFC PATCH 2/3] mm: arch: Use new hugetlb size encoding definitions Mike Kravetz
2017-07-26 9:52 ` Michal Hocko
2017-07-17 22:28 ` [RFC PATCH 3/3] mm: shm: " Mike Kravetz
2017-07-26 9:53 ` Michal Hocko
2017-07-26 10:07 ` Michal Hocko
2017-07-26 17:39 ` Mike Kravetz
2017-07-26 18:48 ` Matthew Wilcox
2017-07-27 7:50 ` Michal Hocko
2017-07-27 21:18 ` Mike Kravetz [this message]
2017-07-28 6:30 ` Michal Hocko
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