lkml.org 
[lkml]   [2019]   [Oct]   [22]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH] hugetlbfs: add O_TMPFILE support
From
Date
On 10/21/19 7:17 PM, Mike Kravetz wrote:
> On 10/15/19 4:37 PM, Mike Kravetz wrote:
>> On 10/15/19 3:50 AM, Michal Hocko wrote:
>>> On Tue 15-10-19 11:01:12, Piotr Sarna wrote:
>>>> With hugetlbfs, a common pattern for mapping anonymous huge pages
>>>> is to create a temporary file first.
>>>
>>> Really? I though that this is normally done by shmget(SHM_HUGETLB) or
>>> mmap(MAP_HUGETLB). Or maybe I misunderstood your definition on anonymous
>>> huge pages.
>>>
>>>> Currently libraries like
>>>> libhugetlbfs and seastar create these with a standard mkstemp+unlink
>>>> trick,
>>
>> I would guess that much of libhugetlbfs was writen before MAP_HUGETLB
>> was implemented. So, that is why it does not make (more) use of that
>> option.
>>
>> The implementation looks to be straight forward. However, I really do
>> not want to add more functionality to hugetlbfs unless there is specific
>> use case that needs it.
>
> It was not my intention to shut down discussion on this patch. I was just
> asking if there was a (new) use case for such a change. I am checking with
> our DB team as I seem to remember them using the create/unlink approach for
> hugetlbfs in one of their upcoming models.
>
> Is there a new use case you were thinking about?
>

Oh, I indeed thought it was a shutdown. The use case I was thinking
about was in Seastar, where the create+unlink trick is used for creating
temporary files (in a generic way, not only for hugetlbfs). I simply
intended to migrate it to a newer approach - O_TMPFILE. However,
for the specific case of hugetlbfs it indeed makes more sense to skip it
and use mmap's MAP_HUGETLB, so perhaps it's not worth it to patch a
perfectly good and stable file system just to provide a semi-useful flag
support. My implementation of tmpfile for hugetlbfs is straightforward
indeed, but the MAP_HUGETLB argument made me realize that it may not be
worth the trouble - especially that MAP_HUGETLB is here since 2.6 and
O_TMPFILE was introduced around v3.11, so the mmap way looks more portable.

tldr: I'd be very happy to get my patch accepted, but the use case I had
in mind can be easily solved with MAP_HUGETLB, so I don't insist.

\
 
 \ /
  Last update: 2019-10-22 09:11    [W:0.060 / U:2.012 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site