linux-kernel - Re: [RFC PATCH v2] Add new elevator ops for request hint

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Message-ID: <4E43DBFB.6020105@fusionio.com>
Date:	Thu, 11 Aug 2011 15:41:15 +0200
From:	Jens Axboe <jaxboe@...ionio.com>
To:	Vivek Goyal <vgoyal@...hat.com>
CC:	Kyungmin Park <kmpark@...radead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"arnd@...db.de" <arnd@...db.de>,
	"jh80.chung@...sung.com" <jh80.chung@...sung.com>,
	"shli@...nel.org" <shli@...nel.org>,
	"linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>
Subject: Re: [RFC PATCH v2] Add new elevator ops for request hint

On 2011-08-11 15:33, Vivek Goyal wrote:
> On Thu, Aug 11, 2011 at 09:42:16AM +0900, Kyungmin Park wrote:
>> Hi Jens
>>
>> Now eMMC device requires the upper layer information to improve the data
>> performance and reliability.
>>
>> . Context ID
>> Using the context information, it can sort out the data internally and improve the performance.
>> The main problem is that it's needed to define "What's the context". 
>> Actually I expect cfq queue has own unique ID but it doesn't so decide to use the pid instead
>>
> 
> Hi,
> 
> Can you please give little more details about the optimization you will
> do with this pid information?

It is provided in one of the other email threads for this patch.

> Also what happens in the case of noop and deadline which don't maintain
> per process queues and can't provide this information.

It'll still work, it isn't really tied to the CFQ way of diviying things
up.

>> First I expect the REQ_META but current ext4 doesn't pass the WRITE_META. only use the READ_META. so it needs to investigate it.
> 
> So are you planning to later fix file systems to appropriately mark meta
> data requests?

One thing that occured to me is that equating META to HOT is not
necessarily a good idea. Meta data isn't necessarily more "hot" than
regular data, it all depends on how it's being used. So I think it would
be a lot more appropriate to pass down this information specifically,
instead of overloading REQ_META.

-- 
Jens Axboe

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