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SubjectRE: [PATCH v3 7/7] fs/ext4,jbd2: add support for passing write-hint with journal
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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@oracle.com]
Sent: Wednesday, April 03, 2019 8:28 AM
To: Kanchan Joshi <joshi.k@samsung.com>
Cc: linux-kernel@vger.kernel.org; linux-block@vger.kernel.org;
linux-nvme@lists.infradead.org; linux-fsdevel@vger.kernel.org;
linux-ext4@vger.kernel.org; axboe@fb.com; prakash.v@samsung.com;
anshul@samsung.com; joshiiitr@gmail.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

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