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

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Message-ID: <536D5DED-FE80-441E-8715-1E5E594C2AF0@vmware.com>
Date:   Tue, 16 Jul 2019 22:06:19 +0000
From:   Nadav Amit <namit@...are.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
CC:     Dan Williams <dan.j.williams@...el.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 Jul 16, 2019, at 3:00 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
> resource-avoid-unnecessary-lookups-in-find_next_iomem_res.patch
> 
> ?

I didn’t get to follow Dan Williams advice. But, both of two patches are
fine on my opinion and should go upstream. The first one fixes a bug and the
second one improves performance considerably (and removes most of the
overhead). Future improvements can go on top of these patches and are not
expected to conflict.

So I think they should go upstream - the first one immediately, the second
one when possible.