linux-kernel - RE: [PATCH v3 7/7] fs/ext4,jbd2: add support for passing write-hint with journal

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Date:   Wed, 3 Apr 2019 19:12:00 +0530
From:   "kanchan" <joshi.k@...sung.com>
To:     "'Martin K. Petersen'" <martin.petersen@...cle.com>
Cc:     <linux-kernel@...r.kernel.org>, <linux-block@...r.kernel.org>,
        <linux-nvme@...ts.infradead.org>, <linux-fsdevel@...r.kernel.org>,
        <linux-ext4@...r.kernel.org>, <axboe@...com>,
        <prakash.v@...sung.com>, <anshul@...sung.com>,
        <joshiiitr@...il.com>
Subject: RE: [PATCH v3 7/7] fs/ext4,jbd2: add support for passing write-hint
 with journal

Hi Martin,

> Why not just introduce REQ_JOURNAL and let the device driver decide how to
turn that into something appropriate for the device?

It began with that kind of thought/goal i.e.  introduce something just for
FS journal. But it seems to have evolved for good. 
Current approach extends write-hint infra so that whole thing becomes
extensible for other kind of use-cases (than FS journal) as well. 	
Also in this approach, driver will do little, while block-layer will do
majority of the work.

> That's what I'll need for SCSI. Existing SCSI streams are not a good fit.

Do you see that it's difficult for SCSI to use write-hint infrastructure for
streams? 


  
-----Original Message-----
From: Martin K. Petersen [mailto:martin.petersen@...cle.com] 
Sent: Wednesday, April 03, 2019 8:28 AM
To: Kanchan Joshi <joshi.k@...sung.com>
Cc: linux-kernel@...r.kernel.org; linux-block@...r.kernel.org;
linux-nvme@...ts.infradead.org; linux-fsdevel@...r.kernel.org;
linux-ext4@...r.kernel.org; axboe@...com; prakash.v@...sung.com;
anshul@...sung.com; joshiiitr@...il.com
Subject: Re: [PATCH v3 7/7] fs/ext4,jbd2: add support for passing write-hint
with journal


Kanchan,

> For NAND based SSDs, mixing of data with different life-time reduces 
> efficiency of internal garbage-collection. During FS operations, 
> series of journal updates will follow/precede series of data/meta 
> updates, causing intermixing inside SSD. By passing a write-hint with 
> journal, its write can be isolated from other data/meta writes, 
> leading to endurance/performance benefit on SSD.

Why not just introduce REQ_JOURNAL and let the device driver decide how to
turn that into something appropriate for the device?

That's what I'll need for SCSI. Existing SCSI streams are not a good fit.

-- 
Martin K. Petersen	Oracle Linux Engineering