Re: [RFC 0/3] hugetlbfs: optionally reserve all fs pages at mount time

[Mike Kravetz]

On 03/06/2015 01:14 PM, David Rientjes wrote:
> On Fri, 6 Mar 2015, Mike Kravetz wrote:
>
> > Thanks for the CONFIG_CGROUP_HUGETLB suggestion, however I do not
> > believe this will be a satisfactory solution for my usecase.  As you
> > point out, cgroups could be set up (by a sysadmin) for every hugetlb
> > user/application.  In this case, the sysadmin needs to have knowledge
> > of every huge page user/application and configure appropriately.
> >
> > I was approaching this from the point of view of the application.  The
> > application wants the guarantee of a minimum number of huge pages,
> > independent of other users/applications.  The "reserve" approach allows
> > the application to set aside those pages at initialization time.  If it
> > can not get the pages it needs, it can refuse to start, or configure
> > itself to use less, or take other action.
>
> Would it be too difficult to modify the application to mmap() the
> hugepages at startup so they are no longer free in the global pool but
> rather get marked as reserved so other applications cannot map them?  That
> should return MAP_FAILED if there is an insufficient number of hugepages
> available to be reserved (HugePages_Rsvd in /proc/meminfo).

The application is a database with multiple processes/tasks that will
come and go over time.  I thought about having one task do a big
mmap() at initialization time, but then the issue is how to coordinate
with the other tasks and their requests to allocate/free pages.

--
Mike Kravetz
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