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

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Date:   Tue, 02 Apr 2019 22:57:31 -0400
From:   "Martin K. Petersen" <martin.petersen@...cle.com>
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