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Subject: Re: [PATCH 6/6] x86/xen: open code alloc_vm_area in
 arch_gnttab_valloc
To:     Christoph Hellwig <hch@lst.de>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Juergen Gross <jgross@suse.com>,
        Stefano Stabellini <sstabellini@kernel.org>,
        Jani Nikula <jani.nikula@linux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@linux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@intel.com>,
        Minchan Kim <minchan@kernel.org>,
        Nitin Gupta <ngupta@vflare.org>, x86@kernel.org,
        xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org,
        intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org,
        linux-mm@kvack.org
References: <20200918163724.2511-1-hch@lst.de>
 <20200918163724.2511-7-hch@lst.de>
 <0833b9a8-5096-d105-a850-1336150eada1@oracle.com>
 <20200922145819.GA28420@lst.de>
 <ebd69ba1-fc06-3cc7-348e-3cb0004c2a34@oracle.com>
 <20200922152706.GA30633@lst.de>
From:   boris.ostrovsky@oracle.com
Organization: Oracle Corporation
Message-ID: <a3daaf31-d1cd-2bf1-5b2f-aaae32baa7f6@oracle.com>
Date:   Tue, 22 Sep 2020 11:34:35 -0400
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On 9/22/20 11:27 AM, Christoph Hellwig wrote:
> On Tue, Sep 22, 2020 at 11:24:20AM -0400, boris.ostrovsky@oracle.com wrote:
>> On 9/22/20 10:58 AM, Christoph Hellwig wrote:
>>> On Mon, Sep 21, 2020 at 04:44:10PM -0400, boris.ostrovsky@oracle.com wrote:
>>>> This will end up incrementing area->ptes pointer. So perhaps something like
>>>>
>>>>
>>>> pte_t **ptes = area->ptes;
>>>>
>>>> if (apply_to_page_range(&init_mm, (unsigned long)area->area->addr,
>>>>                         PAGE_SIZE * nr_frames, gnttab_apply, &ptes)) {
>>>>
>>>>        ...
>>> Yeah.  What do you think of this version? 
>>
>> Oh yes, this is way better. This now can actually be read without trying to mentally unwind triple pointers. (You probably want to initialize idx to zero before calling apply_to_page_range(), I am not sure it's guaranteed to be zero).
> Both instances are static variables, thus in .bss and initialized.
> So unless you insist I don't think we need a manual one.


Yes, you are right. (I thought perhaps this code could be called more than once but no, it can't).


-boris