linux-ext4 - Re: [PATCH v1 2/2] mm: remove extra ZONE

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Date:   Fri, 15 Oct 2021 08:06:49 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     "Sierra Guiza, Alejandro (Alex)" <alex.sierra@....com>
Cc:     Ralph Campbell <rcampbell@...dia.com>, akpm@...ux-foundation.org,
        Felix.Kuehling@....com, linux-mm@...ck.org,
        linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org,
        amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        hch@....de, jglisse@...hat.com, apopple@...dia.com,
        willy@...radead.org
Subject: Re: [PATCH v1 2/2] mm: remove extra ZONE_DEVICE struct page refcount

On Thu, Oct 14, 2021 at 10:45:52PM -0500, Sierra Guiza, Alejandro (Alex) wrote:
> 
> On 10/14/2021 3:57 PM, Ralph Campbell wrote:
> > 
> > On 10/14/21 11:01 AM, Jason Gunthorpe wrote:
> > > On Thu, Oct 14, 2021 at 10:35:27AM -0700, Ralph Campbell wrote:
> > > 
> > > > I ran xfstests-dev using the kernel boot option to "fake" a pmem device
> > > > when I first posted this patch. The tests ran OK (or at least the same
> > > > tests passed with and without my patch).
> > > Hmm. I know nothing of xfstests but
> > > 
> > > tests/generic/413
> > > 
> > > Looks kind of like it might cover this situation?
> > > 
> > > Did it run for you?
> > > 
> > > Jason
> > 
> > I don't remember. I'll have to rerun the test which might take a day or
> > two
> > to set up again.
> > 
> I just ran this generic/413 on my side using pmem fake device. It does fail.
> I remember we proposed a fix on this patch before try_get_page was
> removed.

Thanks so much, that confirms I've read everything properly!

The fix is to incr the refcount at the proper times, not ignore the
broken refcount

Jason