linux-kernel - Re: [PATCH v2] Support for write stream IDs

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Message-ID: <554A4668.7040804@plexistor.com>
Date:	Wed, 06 May 2015 19:50:48 +0300
From:	Boaz Harrosh <boaz@...xistor.com>
To:	"Martin K. Petersen" <martin.petersen@...cle.com>,
	Jens Axboe <axboe@...com>
CC:	Jeff Moyer <jmoyer@...hat.com>, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, adilger@...ger.ca,
	david@...morbit.com
Subject: Re: [PATCH v2] Support for write stream IDs

On 05/06/2015 01:09 AM, Martin K. Petersen wrote:
>>>>>> "Jens" == Jens Axboe <axboe@...com> writes:
<>
> 
> The only sensible solution is for the kernel to manage the stream
> IDs. And for them to be plentiful. The storage device is free to ignore
> them, do LRU or whatever it pleases to manage them if it has an internal
> limit on number of open streams, etc.
> 

Sometimes you do not have control over the "storage device" firmware
and/or it is already too late. But in such a case the LLD of the device
can do the state management (open/close) and translation (LRU).
If there are a lot of broken devices with the same small size that need
an LRU and/or state, bunch of LLDs can reuse a common library.

But hey yes I'm with Martin here. It sounds like a filesystem thing
and not an application thing.

>From the application side we already have the O_TMP hint and other
fadvise hits, but it is more the filesystem policy of what to do
with this.

Also current proposed solution for application is kind of a layering
violation. I set an Id at the filesystem level API: Open a file,
set an ID. But I acquire the ID from the block device under
the FS. This will never map well. In fact it calls for only a very
hard-coded hardware specific application that can use this.

Thanks
Boaz

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