Re: [RFC] blk: increase logical_block_size to unsigned int

[Jerome Marchand]

----- Original Message -----
> From: "Sergey Senozhatsky" <sergey.senozhatsky@xxxxxxxxx>
> To: "Minchan Kim" <minchan@xxxxxxxxxx>
> Cc: "Jens Axboe" <axboe@xxxxxxxxx>, "Hyeoncheol Lee" <cheol.lee@xxxxxxx>, linux-block@xxxxxxxxxxxxxxx,
> linux-kernel@xxxxxxxxxxxxxxx, "Andrew Morton" <akpm@xxxxxxxxxxxxxxxxxxxx>, "Sergey Senozhatsky"
> <sergey.senozhatsky@xxxxxxxxx>, "Robert Jennings" <rcj@xxxxxxxxxxxxxxxxxx>, "Jerome Marchand" <jmarchan@xxxxxxxxxx>
> Sent: Monday, January 9, 2017 3:33:44 PM
> Subject: Re: [RFC] blk: increase logical_block_size to unsigned int
> 
> 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.

Jerome

> 
> 	-ss
>