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

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Date:   Wed, 14 Jun 2017 09:49:50 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Jan Kara <jack@...e.cz>
Cc:     "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
        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>,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v3 13/14] filesystem-dax: gate calls to dax_flush() on QUEUE_FLAG_WC

On Wed, Jun 14, 2017 at 3:46 AM, Jan Kara <jack@...e.cz> wrote:
> On Fri 09-06-17 13:24:56, 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.
>>
>> Cc: Jan Kara <jack@...e.cz>
>> Cc: Jeff Moyer <jmoyer@...hat.com>
>> Cc: Christoph Hellwig <hch@....de>
>> Cc: Matthew Wilcox <mawilcox@...rosoft.com>
>> Cc: Ross Zwisler <ross.zwisler@...ux.intel.com>
>> Signed-off-by: Dan Williams <dan.j.williams@...el.com>
>
> ...
>
>> -     dax_flush(dax_dev, pgoff, kaddr, size);
>> +     if (test_bit(QUEUE_FLAG_WC, &bdev->bd_queue->queue_flags))
>> +             dax_flush(dax_dev, pgoff, kaddr, size);
>
> IMHO the check belongs into dax_flush() similarly as blkdev_issue_flush()
> takes silently handles whether the flush is actually needed or not.

Looks good, will do.