Subject: Re: [PATCH 5/9] block: add ability to flag write back caching on a
 device
To: Christoph Hellwig <hch@infradead.org>
References: <1459350477-16404-1-git-send-email-axboe@fb.com>
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 <20160330154241.GA13131@infradead.org>
CC: <linux-kernel@vger.kernel.org>, <linux-fsdevel@vger.kernel.org>,
        <linux-block@vger.kernel.org>
From: Jens Axboe <axboe@fb.com>
Message-ID: <56FBF4D8.9000203@fb.com>
Date: Wed, 30 Mar 2016 09:46:32 -0600
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On 03/30/2016 09:42 AM, Christoph Hellwig wrote:
> On Wed, Mar 30, 2016 at 09:07:53AM -0600, Jens Axboe wrote:
>> Add an internal helper and flag for setting whether a queue has
>> write back caching, or write through (or none). Add a sysfs file
>> to show this as well, and make it changeable from user space.
>
> As per previous discussion:  I don't really care about the way how we
> tell the block layer we have a writeback cache, but a NAK to having
> each driver call two interfaces to convey the same information.
>
> Please just look at q->flush_flag & REQ_FLUSH for now, and then
> improvem the interface if you don't like it (I don't particularly like
> it, but not to the point that I'm motivated enough to fix it :))

That's fine, I don't mind making that change, just didn't do it for this 
version. I prefer if we change the cache flagging to be the primary way 
to signal it, it's more intuitive than REQ_FLUSH.

It'll be in the next version.

-- 
Jens Axboe