linux-kernel - Re: [PATCH v7 3/8] fsdax: Replace mmap entry in case of CoW

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Message-ID: <6e86fe6e-fcbb-908c-11a4-4c322199bc5e@fujitsu.com>
Date:   Fri, 27 Aug 2021 13:26:41 +0800
From:   Shiyang Ruan <ruansy.fnst@...itsu.com>
To:     Dan Williams <dan.j.williams@...el.com>
CC:     Christoph Hellwig <hch@....de>,
        "Darrick J. Wong" <djwong@...nel.org>,
        linux-xfs <linux-xfs@...r.kernel.org>,
        david <david@...morbit.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux NVDIMM <nvdimm@...ts.linux.dev>,
        Goldwyn Rodrigues <rgoldwyn@...e.de>,
        Al Viro <viro@...iv.linux.org.uk>,
        Matthew Wilcox <willy@...radead.org>,
        Goldwyn Rodrigues <rgoldwyn@...e.com>,
        Ritesh Harjani <riteshh@...ux.ibm.com>
Subject: Re: [PATCH v7 3/8] fsdax: Replace mmap entry in case of CoW



On 2021/8/27 13:00, Dan Williams wrote:
> On Thu, Aug 26, 2021 at 8:22 PM Shiyang Ruan <ruansy.fnst@...itsu.com> wrote:
>>
>>
>>
>> On 2021/8/23 20:57, Christoph Hellwig wrote:
>>> On Thu, Aug 19, 2021 at 03:54:01PM -0700, Dan Williams wrote:
>>>>
>>>> static void *dax_insert_entry(struct xa_state *xas, struct vm_fault *vmf,
>>>>                                 const struct iomap_iter *iter, void
>>>> *entry, pfn_t pfn,
>>>>                                 unsigned long flags)
>>>>
>>>>
>>>>>    {
>>>>> +       struct address_space *mapping = vmf->vma->vm_file->f_mapping;
>>>>>           void *new_entry = dax_make_entry(pfn, flags);
>>>>> +       bool dirty = insert_flags & DAX_IF_DIRTY;
>>>>> +       bool cow = insert_flags & DAX_IF_COW;
>>>>
>>>> ...and then calculate these flags from the source data. I'm just
>>>> reacting to "yet more flags".
>>>
>>> Except for the overly long line above that seems like a good idea.
>>> The iomap_iter didn't exist for most of the time this patch has been
>>> around.
>>>
>>
>> So should I reuse the iter->flags to pass the insert_flags? (left shift
>> it to higher bits)
> 
> No, the advice is to just pass the @iter to dax_insert_entry directly
> and calculate @dirty and @cow internally.
> 

I see.  Yes, they can be calculated inside the dax_insert_entry() 
because it already has enough arguments.


--
Thanks,
Ruan.