linux-kernel - Re: [PATCH RFC] hugetlbfs 'noautofill' mount option

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Message-ID: <1031e0d4-cdbb-db8b-dae7-7c733921e20e@oracle.com>
Date:   Tue, 9 May 2017 13:59:34 -0700
From:   Prakash Sangappa <prakash.sangappa@...cle.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Dave Hansen <dave.hansen@...el.com>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH RFC] hugetlbfs 'noautofill' mount option

On 5/9/17 1:58 AM, Christoph Hellwig wrote:
> On Mon, May 08, 2017 at 03:12:42PM -0700, prakash.sangappa wrote:
>> Regarding #3 as a general feature, do we want to
>> consider this and the complexity associated with the
>> implementation?
> We have to.  Given that no one has exclusive access to hugetlbfs
> a mount option is fundamentally the wrong interface.

A hugetlbfs filesystem may need to be mounted for exclusive use by
an application. Note, recently the 'min_size' mount option was added
to hugetlbfs, which would reserve minimum number of huge pages
for that filesystem for use by an application. If the filesystem with
min size specified, is not setup for exclusive use by an application,
then the purpose of reserving huge pages is defeated.  The
min_size option was for use by applications like the database.

Also, I am investigating enabling hugetlbfs mounts within user
namespace's mount namespace. That would allow an application
to mount a hugetlbfs filesystem inside a namespace exclusively for
its use, running as a non root user. For this it seems like the 'min_size'
should be subject to some user limits. Anyways, mounting inside
user namespaces is  a different discussion.

So, if a filesystem has to be setup for exclusive use by an application,
then different mount options can be used for that filesystem.