linux-ext4 - Re: [PATCH v2 0/4] Write-hint for FS journal

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Date:   Mon, 28 Jan 2019 16:24:24 -0700
From:   Keith Busch <keith.busch@...el.com>
To:     Jan Kara <jack@...e.cz>
Cc:     Kanchan Joshi <joshi.k@...sung.com>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
        "linux-nvme@...ts.infradead.org" <linux-nvme@...ts.infradead.org>,
        "jack@...e.com" <jack@...e.com>,
        "david@...morbit.com" <david@...morbit.com>,
        "tytso@....edu" <tytso@....edu>,
        "prakash.v@...sung.com" <prakash.v@...sung.com>
Subject: Re: [PATCH v2 0/4] Write-hint for FS journal

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?