linux-kernel - correction: Re: [PATCH 4/6] dm,dax,pmem: prepare dax_copy_to/from_iter() APIs with DAXDEV_F

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Date:   Fri, 22 Oct 2021 01:41:16 +0000
From:   Jane Chu <jane.chu@...cle.com>
To:     Christoph Hellwig <hch@...radead.org>
CC:     "david@...morbit.com" <david@...morbit.com>,
        "djwong@...nel.org" <djwong@...nel.org>,
        "dan.j.williams@...el.com" <dan.j.williams@...el.com>,
        "vishal.l.verma@...el.com" <vishal.l.verma@...el.com>,
        "dave.jiang@...el.com" <dave.jiang@...el.com>,
        "agk@...hat.com" <agk@...hat.com>,
        "snitzer@...hat.com" <snitzer@...hat.com>,
        "dm-devel@...hat.com" <dm-devel@...hat.com>,
        "ira.weiny@...el.com" <ira.weiny@...el.com>,
        "willy@...radead.org" <willy@...radead.org>,
        "vgoyal@...hat.com" <vgoyal@...hat.com>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "nvdimm@...ts.linux.dev" <nvdimm@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-xfs@...r.kernel.org" <linux-xfs@...r.kernel.org>
Subject: correction: Re: [PATCH 4/6] dm,dax,pmem: prepare
 dax_copy_to/from_iter() APIs with DAXDEV_F_RECOVERY

On 10/21/2021 5:49 PM, Jane Chu wrote:
> On 10/21/2021 4:27 AM, Christoph Hellwig wrote:
>> On Wed, Oct 20, 2021 at 06:10:57PM -0600, Jane Chu wrote:
>>> Prepare dax_copy_to/from_iter() APIs with DAXDEV_F_RECOVERY flag
>>> such that when the flag is set, the underlying driver implementation
>>> of the APIs may deal with potential poison in a given address
>>> range and read partial data or write after clearing poison.
>>
>> FYI, I've been wondering for a while if we could just kill off these
>> methods entirely.  Basically the driver interaction consists of two
>> parts:
>>
>>    a) wether to use the flushcache/mcsafe variants of the generic helpers
>>    b) actually doing remapping for device mapper
>>
>> to me it seems like we should handle a) with flags in dax_operations,
>> and only have a remap callback for device mapper.  That way we'd avoid
>> the indirect calls for the native case, and also avoid tons of
>> boilerplate code.  "futher decouple DAX from block devices" series
>> already massages the device mapper into a form suitable for such
>> callbacks.
>>
> 
> I've looked through your "futher decouple DAX from block devices" series
> and likes the use of xarray in place of the host hash list.
> Which upstream version is the series based upon?
> If it's based on your development repo, I'd be happy to take a clone
> and rebase my patches on yours if you provide a link. Please let me
> know the best way to cooperate.
> 
> That said, I'm unclear at what you're trying to suggest with respect
> to the 'DAXDEV_F_RECOVERY' flag.  The flag came from upper dax-fs
> call stack to the dm target layer, and the dm targets are equipped
> with handling pmem driver specific task, so it appears that the flag

Apologies. The above line should be
"..., and the dm targets are _not_ equipped with handling pmem driver
specific task,"

-jane


> would need to be passed down to the native pmem layer, right?
> Am I totally missing your point?
> 
> thanks,
> -jane
>