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From: Dave Chinner <david@fromorbit.com>
To: Jan Kara <jack@suse.cz>
Cc: Keith Busch <keith.busch@intel.com>,
	Kanchan Joshi <joshi.k@samsung.com>,
	"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
	"linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
	"linux-ext4@vger.kernel.org" <linux-ext4@vger.kernel.org>,
	"linux-nvme@lists.infradead.org" <linux-nvme@lists.infradead.org>,
	"jack@suse.com" <jack@suse.com>, "tytso@mit.edu" <tytso@mit.edu>,
	"prakash.v@samsung.com" <prakash.v@samsung.com>,
	Jens Axboe <axboe@kernel.dk>
Subject: Re: [PATCH v2 0/4] Write-hint for FS journal
Date: Wed, 30 Jan 2019 11:13:49 +1100
Message-ID: <20190130001349.GT6173@dastard> (raw)
In-Reply-To: <20190129100702.GA29981@quack2.suse.cz>

On Tue, Jan 29, 2019 at 11:07:02AM +0100, Jan Kara wrote:
> On Mon 28-01-19 16:24:24, Keith Busch wrote:
> > On Mon, Jan 28, 2019 at 04:47:09AM -0800, Jan Kara wrote:
> > > On Fri 25-01-19 09:23:53, Keith Busch wrote:
> > > > On Wed, Jan 09, 2019 at 09:00:57PM +0530, Kanchan Joshi wrote:
> > > > > Towards supporing write-hints/streams for filesystem journal.                   
> > > > >                                                                                 
> > > > > Here is the v1 patch for background -                                           
> > > > > https://marc.info/?l=linux-fsdevel&m=154444637519020&w=2                        
> > > > >                                                                                 
> > > > > Changes since v1:                                                               
> > > > > - introduce four more hints for in-kernel use, as recommended by Dave chinner   
> > > > >   & Jens axboe. This isolates kernel-mode hints from user-mode ones.            
> > > > 
> > > > The nvme driver disables streams if the controller doesn't support
> > > > BLK_MAX_WRITE_HINT number of streams, so this series breaks the feature
> > > > for controllers that only support up to 4.
> > > 
> > > Right. Do you know if there are such controllers? Or are you just afraid
> > > that there could be?
> > 
> > I've asked around, and the concensus I received is all currently support
> > at least 8, but they couldn't say if that would be true for potential
> > lower budget products. Can we implement a reasonable fallback to use
> > what's available?
> 
> OK, thanks for input. So probably we should just map kernel stream IDs to 0
> if the device doesn't support them. But that probably means we need to
> propagate number of available streams up from NVME into the block layer so
> that this can be handled reasonably seamlessly. Jens, Kanchan?

Yeah, that's basically what I said we needed to do when this was
last discussed. i.e. that the block layer needed to know how many
streams the hardware had and map the 4 "kernel internal" hints
appropriately to what he device supports.

e.g. if the device only supports 4 hints, then it needs to map the
kernel hints either to zero. If it supports less than 8 streams,
then they need otbe mapped into the hints above index 5. If there
are N streams, then they need to be mapped to the hints {N-3,N}

And, to top it all off, there needs to be guards so that if we want
to grow the userspace hints to more than 4 hints, they don't crash
into ranges the kernel is already reserving because of limited
device range support.

Nothing is ever simple....

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com

  reply index

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <CGME20190109153328epcas2p4643cbdc7a2182b47893a2bcaa0778e17@epcas2p4.samsung.com>
2019-01-09 15:30 ` Kanchan Joshi
     [not found]   ` <CGME20190109153332epcas1p187b419176a8d1d0be4982a275c0b9e86@epcas1p1.samsung.com>
2019-01-09 15:30     ` [PATCH 1/4] block: Increase count of supported write-hints Kanchan Joshi
     [not found]   ` <CGME20190109153336epcas2p29b3275b6c545e483a3f43b92268f08bf@epcas2p2.samsung.com>
2019-01-09 15:30     ` [PATCH 2/4] fs: introduce four macros for in-kernel hints Kanchan Joshi
2019-01-23 18:27       ` [PATCH 2/4] " Javier González
2019-01-24  8:35         ` Jan Kara
2019-01-24  9:23           ` Javier González
     [not found]   ` <CGME20190109153339epcas2p4691a898dde0174a7565d62fcb3be0b6d@epcas2p4.samsung.com>
2019-01-09 15:31     ` [PATCH 3/4] fs: introduce APIs to enable sending write-hint with buffer-head Kanchan Joshi
     [not found]   ` <CGME20190109153342epcas2p3208f62a4dd876f8e1765b48f8aec2432@epcas2p3.samsung.com>
2019-01-09 15:31     ` [PATCH 4/4] fs/ext4,jbd2: add support for passing write-hint with journal Kanchan Joshi
2019-01-24  8:50       ` Jan Kara
2019-01-23 18:35   ` [PATCH v2 0/4] Write-hint for FS journal Javier González
2019-01-24  8:29   ` Jan Kara
2019-01-25 14:20     ` Kanchan Joshi
2019-01-25 16:23   ` Keith Busch
2019-01-28 12:47     ` Jan Kara
2019-01-28 23:24       ` Keith Busch
2019-01-29 10:07         ` Jan Kara
2019-01-30  0:13           ` Dave Chinner [this message]
2019-01-30 13:54             ` Kanchan Joshi
2019-02-05 11:50               ` Jan Kara
2019-02-05 22:53                 ` Dave Chinner

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