linux-kernel - Re: [PATCH v3 13/14] filesystem-dax: gate calls to dax_flush() on QUEUE_FLAG

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Message-ID: <CAPcyv4gk_0d-aykn2WQJSTArpR+fReWmtY_5=TLpW_uHPbNEeA@mail.gmail.com>
Date:   Sun, 18 Jun 2017 19:07:10 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Christoph Hellwig <hch@....de>
Cc:     "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
        Jan Kara <jack@...e.cz>, dm-devel@...hat.com,
        Matthew Wilcox <mawilcox@...rosoft.com>,
        X86 ML <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Jeff Moyer <jmoyer@...hat.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Ross Zwisler <ross.zwisler@...ux.intel.com>
Subject: Re: [PATCH v3 13/14] filesystem-dax: gate calls to dax_flush() on QUEUE_FLAG_WC

On Sun, Jun 18, 2017 at 1:45 AM, Christoph Hellwig <hch@....de> wrote:
> On Fri, Jun 09, 2017 at 01:24:56PM -0700, Dan Williams wrote:
>> Some platforms arrange for cpu caches to be flushed on power-fail. On
>> those platforms there is no requirement that the kernel track and flush
>> potentially dirty cache lines. Given that we still insert entries into
>> the radix for locking purposes this patch only disables the cache flush
>> loop, not the dirty tracking.
>>
>> Userspace can override the default cache setting via the block device
>> queue "write_cache" attribute in sysfs.
>
> NAK.  Please stop using the block infrastructure for dax values.  Have
> your own flag and sysfs file in the dax infrastructure and only propagate
> it to the block layer for the block devices using dax.

Ok, that makes sense.