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Date:   Thu, 19 Nov 2020 20:27:02 -0500
From:   John Dorminy <jdorminy@...hat.com>
To:     "Leizhen (ThunderTown)" <thunder.leizhen@...wei.com>
Cc:     Coly Li <colyli@...e.de>, Jens Axboe <axboe@...nel.dk>,
        Kent Overstreet <kent.overstreet@...il.com>,
        Alasdair Kergon <agk@...hat.com>,
        Mike Snitzer <snitzer@...hat.com>,
        dm-devel <dm-devel@...hat.com>,
        linux-block <linux-block@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-bcache <linux-bcache@...r.kernel.org>
Subject: Re: [PATCH 1/1] block: move the PAGE_SECTORS definition into <linux/blkdev.h>

Greetings;

There are a lot of uses of PAGE_SIZE/SECTOR_SIZE scattered around, and
it seems like a medium improvement to be able to refer to it as
PAGE_SECTORS everywhere instead of just inside dm, bcache, and
null_blk. Did this change progress forward somewhere?

Thanks!

John Dorminy


On Mon, Sep 7, 2020 at 3:40 AM Leizhen (ThunderTown)
<thunder.leizhen@...wei.com> wrote:
>
> Hi, Jens Axboe, Alasdair Kergon, Mike Snitzer:
>   What's your opinion?
>
>
> On 2020/8/21 15:05, Coly Li wrote:
> > On 2020/8/21 14:48, Leizhen (ThunderTown) wrote:
> >>
> >>
> >> On 8/21/2020 12:11 PM, Coly Li wrote:
> >>> On 2020/8/21 10:03, Zhen Lei wrote:
> >>>> There are too many PAGE_SECTORS definitions, and all of them are the
> >>>> same. It looks a bit of a mess. So why not move it into <linux/blkdev.h>,
> >>>> to achieve a basic and unique definition.
> >>>>
> >>>> Signed-off-by: Zhen Lei <thunder.leizhen@...wei.com>
> >>>
> >>>
> >>> A lazy question about page size > 4KB: currently in bcache code the
> >>> sector size is assumed to be 512 sectors, if kernel page > 4KB, it is
> >>> possible that PAGE_SECTORS in bcache will be a number > 8 ?
> >>
> >> Sorry, I don't fully understand your question. I known that the sector size
> >> can be 512 or 4K, and the PAGE_SIZE can be 4K or 64K. So even if sector size
> >> is 4K, isn't it greater than 8 for 64K pages?
> >>
> >> I'm not sure if the question you're asking is the one Matthew Wilcox has
> >> answered before:
> >> https://www.spinics.net/lists/raid/msg64345.html
> >
> > Thank you for the above information. Currently bcache code assumes
> > sector size is always 512 bytes, you may see how many "<< 9" or ">> 9"
> > are used. Therefore I doubt whether current code may stably work on e.g.
> > 4Kn SSDs (this is only doubt because I don't have such SSD).
> >
> > Anyway your patch is fine to me. This change to bcache doesn't make
> > thins worse or better, maybe it can be helpful to trigger my above
> > suspicious early if people do have this kind of problem on 4Kn sector SSDs.
> >
> > For the bcache part of this patch, you may add,
> > Acked-by: Coly Li <colyli@...e.de>
> >
> > Thanks.
> >
> > Coly Li
> >
> >>>> ---
> >>>>  drivers/block/brd.c           | 1 -
> >>>>  drivers/block/null_blk_main.c | 1 -
> >>>>  drivers/md/bcache/util.h      | 2 --
> >>>>  include/linux/blkdev.h        | 5 +++--
> >>>>  include/linux/device-mapper.h | 1 -
> >>>>  5 files changed, 3 insertions(+), 7 deletions(-)
> >>>>
> >>>
> >>> [snipped]
> >>>
> >>>> diff --git a/drivers/md/bcache/util.h b/drivers/md/bcache/util.h
> >>>> index c029f7443190805..55196e0f37c32c6 100644
> >>>> --- a/drivers/md/bcache/util.h
> >>>> +++ b/drivers/md/bcache/util.h
> >>>> @@ -15,8 +15,6 @@
> >>>>
> >>>>  #include "closure.h"
> >>>>
> >>>> -#define PAGE_SECTORS              (PAGE_SIZE / 512)
> >>>> -
> >>>>  struct closure;
> >>>>
> >>>>  #ifdef CONFIG_BCACHE_DEBUG
> >>>> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
> >>>> index bb5636cc17b91a7..b068dfc5f2ef0ab 100644
> >>>> --- a/include/linux/blkdev.h
> >>>> +++ b/include/linux/blkdev.h
> >>>> @@ -949,11 +949,12 @@ static inline struct request_queue *bdev_get_queue(struct block_device *bdev)
> >>>>   * multiple of 512 bytes. Hence these two constants.
> >>>>   */
> >>>>  #ifndef SECTOR_SHIFT
> >>>> -#define SECTOR_SHIFT 9
> >>>> +#define SECTOR_SHIFT              9
> >>>>  #endif
> >>>>  #ifndef SECTOR_SIZE
> >>>> -#define SECTOR_SIZE (1 << SECTOR_SHIFT)
> >>>> +#define SECTOR_SIZE               (1 << SECTOR_SHIFT)
> >>>>  #endif
> >>>> +#define PAGE_SECTORS              (PAGE_SIZE / SECTOR_SIZE)
> >>>>
> >>>>  /*
> >>>>   * blk_rq_pos()                   : the current sector
> >>> [snipped]
> >>>
> >>>
> >>
> >
> >
> > .
> >
>

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