linux-kernel - Re: [PATCH 0/3] resource: find_next_iomem

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Date:   Tue, 16 Jul 2019 15:07:01 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Nadav Amit <namit@...are.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>, Borislav Petkov <bp@...e.de>,
        Toshi Kani <toshi.kani@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH 0/3] resource: find_next_iomem_res() improvements

On Tue, Jul 16, 2019 at 3:01 PM Andrew Morton <akpm@...ux-foundation.org> wrote:
>
> On Tue, 18 Jun 2019 21:56:43 +0000 Nadav Amit <namit@...are.com> wrote:
>
> > > ...and is constant for the life of the device and all subsequent mappings.
> > >
> > >> Perhaps you want to cache the cachability-mode in vma->vm_page_prot (which I
> > >> see being done in quite a few cases), but I don’t know the code well enough
> > >> to be certain that every vma should have a single protection and that it
> > >> should not change afterwards.
> > >
> > > No, I'm thinking this would naturally fit as a property hanging off a
> > > 'struct dax_device', and then create a version of vmf_insert_mixed()
> > > and vmf_insert_pfn_pmd() that bypass track_pfn_insert() to insert that
> > > saved value.
> >
> > Thanks for the detailed explanation. I’ll give it a try (the moment I find
> > some free time). I still think that patch 2/3 is beneficial, but based on
> > your feedback, patch 3/3 should be dropped.
>
> It has been a while.  What should we do with
>
> resource-fix-locking-in-find_next_iomem_res.patch

This one looks obviously correct to me, you can add:

Reviewed-by: Dan Williams <dan.j.williams@...el.com>

> resource-avoid-unnecessary-lookups-in-find_next_iomem_res.patch

This one is a good bug report that we need to go fix pgprot lookups
for dax, but I don't think we need to increase the trickiness of the
core resource lookup code in the meantime.