linux-kernel - Re: [PATCH] mm: fix hugetlb page unmap count balance issue

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Message-Id: <20230607140001.6685b0a058511f125a005da4@linux-foundation.org>
Date:   Wed, 7 Jun 2023 14:00:01 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Mike Kravetz <mike.kravetz@...cle.com>
Cc:     Gerd Hoffmann <kraxel@...hat.com>,
        Junxiao Chang <junxiao.chang@...el.com>,
        kirill.shutemov@...ux.intel.com, mhocko@...e.com,
        jmarchan@...hat.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, muchun.song@...ux.dev,
        Vivek Kasireddy <vivek.kasireddy@...el.com>,
        Dongwon Kim <dongwon.kim@...el.com>,
        James Houghton <jthoughton@...gle.com>,
        dri-devel@...ts.freedesktop.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH] mm: fix hugetlb page unmap count balance issue

On Wed, 7 Jun 2023 13:53:10 -0700 Mike Kravetz <mike.kravetz@...cle.com> wrote:

> > 
> > BUGs aren't good.  Can we please find a way to push this along?
> > 
> > Have we heard anything from any udmabuf people?
> > 
> 
> I have not heard anything.  When this issue popped up, it took me by surprise.
> 
> udmabuf maintainer (Gerd Hoffmann), the people who added hugetlb support and
> the list where udmabuf was developed (dri-devel@...ts.freedesktop.org) have
> been on cc.

Maybe Greg can suggest a way forward.

> My 'gut reaction' would be to remove hugetlb support from udmabuf.  From a
> quick look, if we really want this support then there will need to be some
> API changes.  For example UDMABUF_CREATE should be hugetlb page aligned
> and a multiple of hugetlb page size if using a hugetlb mapping.
> 
> It would be good to know about users of the driver.

So disabling "hugetlb=on" (and adding an explanatory printk) would
suffice for now?