linux-kernel - Re: [PATCH 5/9] block: add ability to flag write back caching on a device

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Message-ID: <56FBFD96.9020501@fb.com>
Date:	Wed, 30 Mar 2016 10:23:50 -0600
From:	Jens Axboe <axboe@...com>
To:	Christoph Hellwig <hch@...radead.org>
CC:	<linux-kernel@...r.kernel.org>, <linux-fsdevel@...r.kernel.org>,
	<linux-block@...r.kernel.org>
Subject: Re: [PATCH 5/9] block: add ability to flag write back caching on a
 device

On 03/30/2016 09:46 AM, Jens Axboe wrote:
> 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.

Conversion series in here now:

http://git.kernel.dk/cgit/linux-block/log/?h=wb-buf-throttle

-- 
Jens Axboe