linux-kernel - Re: [RFC] blk: increase logical_block

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Date:   Wed, 11 Jan 2017 07:54:27 +0900
From:   Minchan Kim <minchan@...nel.org>
To:     Jerome Marchand <jmarchan@...hat.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Jens Axboe <axboe@...nel.dk>,
        Hyeoncheol Lee <cheol.lee@....com>,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Robert Jennings <rcj@...ux.vnet.ibm.com>
Subject: Re: [RFC] blk: increase logical_block_size to unsigned int

Hi Jerome, Sergey

On Mon, Jan 09, 2017 at 10:09:20AM -0500, Jerome Marchand wrote:
> 
> 
> ----- Original Message -----
> > From: "Sergey Senozhatsky" <sergey.senozhatsky@...il.com>
> > To: "Minchan Kim" <minchan@...nel.org>
> > Cc: "Jens Axboe" <axboe@...nel.dk>, "Hyeoncheol Lee" <cheol.lee@....com>, linux-block@...r.kernel.org,
> > linux-kernel@...r.kernel.org, "Andrew Morton" <akpm@...ux-foundation.org>, "Sergey Senozhatsky"
> > <sergey.senozhatsky@...il.com>, "Jerome Marchand" <jmarchan@...hat.com>
> > Sent: Monday, January 9, 2017 3:33:44 PM
> > Subject: Re: [RFC] blk: increase logical_block_size to unsigned int

Remove Robert's mail. It didn't work and don't know his update mail

> > 
> > On (01/09/17 14:04), Minchan Kim wrote:
> > > Mostly, zram is used as swap system on embedded world so it want to do IO
> > > as PAGE_SIZE aligned/size IO unit. For that, one of the problem was
> > > blk_queue_logical_block_size(zram->disk->queue, PAGE_SIZE) made overflow
> > > in *64K page system* so [1] changed it to constant 4096.
> > > Since that, partial IO can happen so zram should handle it which makes zram
> > > complicated[2].
> > > 
> > 
> > I thought that zram partial IO support is there because some file
> > systems cannot cope with large logical_block_size. like FAT, for
> > example. am I wrong?
> 
> Yes indeed. When we discussed the patch adding the partial I/O, increasing the
> size of logical_block was considered. The reason we didn't go the easy path was
> that not all block users could handle 64k blocks. FAT is one of them.


I thought it might make some FSes which doesn't support 64K block but
I didn't know what FSes exactly. I thought most popular FSes in linux
may work well(e.g., ext, btrfs, xfs). Thanks for the pointer.
I guess there might be more as well as FAT so let's keep it.

Thanks, Sergey and Jerome!