linux-kernel - Re: [PATCH v9 10/10] fsdax: set a CoW flag when associate reflink mappings

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Date:   Fri, 21 Jan 2022 16:34:18 +0800
From:   Shiyang Ruan <ruansy.fnst@...itsu.com>
To:     Christoph Hellwig <hch@...radead.org>
CC:     <linux-kernel@...r.kernel.org>, <linux-xfs@...r.kernel.org>,
        <nvdimm@...ts.linux.dev>, <linux-mm@...ck.org>,
        <linux-fsdevel@...r.kernel.org>, <djwong@...nel.org>,
        <dan.j.williams@...el.com>, <david@...morbit.com>,
        <jane.chu@...cle.com>
Subject: Re: [PATCH v9 10/10] fsdax: set a CoW flag when associate reflink
 mappings



在 2022/1/21 15:16, Christoph Hellwig 写道:
> On Fri, Jan 21, 2022 at 10:33:58AM +0800, Shiyang Ruan wrote:
>>>
>>> But different question, how does this not conflict with:
>>>
>>> #define PAGE_MAPPING_ANON       0x1
>>>
>>> in page-flags.h?
>>
>> Now we are treating dax pages, so I think its flags should be different from
>> normal page.  In another word, PAGE_MAPPING_ANON is a flag of rmap mechanism
>> for normal page, it doesn't work for dax page.  And now, we have dax rmap
>> for dax page.  So, I think this two kinds of flags are supposed to be used
>> in different mechanisms and won't conflect.
> 
> It just needs someone to use folio_test_anon in a place where a DAX
> folio can be passed.  This probably should not happen, but we need to
> clearly document that.
> 
>>> Either way I think this flag should move to page-flags.h and be
>>> integrated with the PAGE_MAPPING_FLAGS infrastucture.
>>
>> And that's why I keep them in this dax.c file.
> 
> But that does not integrate it with the infrastructure.  For people
> to debug things it needs to be next to PAGE_MAPPING_ANON and have
> documentation explaining why they are exclusive.

Ok, understood.


--
Thanks,
Ruan.