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From: Mike Snitzer <snitzer@redhat.com>
To: Christoph Hellwig <hch@lst.de>
Cc: Jens Axboe <axboe@kernel.dk>,
	linux-raid@vger.kernel.org, martin.petersen@oracle.com,
	Hans de Goede <hdegoede@redhat.com>,
	Richard Weinberger <richard@nod.at>,
	Minchan Kim <minchan@kernel.org>,
	drbd-dev@tron.linbit.com, linux-kernel@vger.kernel.org,
	linux-block@vger.kernel.org, Song Liu <song@kernel.org>,
	dm-devel@redhat.com, linux-mtd@lists.infradead.org,
	linux-fsdevel@vger.kernel.org, cgroups@vger.kernel.org,
	linux-mm@kvack.org
Subject: Re: [PATCH 06/14] block: lift setting the readahead size into the block layer
Date: Thu, 10 Sep 2020 13:15:41 -0400
Message-ID: <20200910171541.GB21919@redhat.com> (raw)
In-Reply-To: <20200910092813.GA27229@lst.de>

On Thu, Sep 10 2020 at  5:28am -0400,
Christoph Hellwig <hch@lst.de> wrote:

> On Wed, Sep 02, 2020 at 12:20:07PM -0400, Mike Snitzer wrote:
> > On Wed, Sep 02 2020 at 11:11am -0400,
> > Christoph Hellwig <hch@lst.de> wrote:
> > 
> > > On Wed, Aug 26, 2020 at 06:07:38PM -0400, Mike Snitzer wrote:
> > > > On Sun, Jul 26 2020 at 11:03am -0400,
> > > > Christoph Hellwig <hch@lst.de> wrote:
> > > > 
> > > > > Drivers shouldn't really mess with the readahead size, as that is a VM
> > > > > concept.  Instead set it based on the optimal I/O size by lifting the
> > > > > algorithm from the md driver when registering the disk.  Also set
> > > > > bdi->io_pages there as well by applying the same scheme based on
> > > > > max_sectors.
> > > > > 
> > > > > Signed-off-by: Christoph Hellwig <hch@lst.de>
> > > > > ---
> > > > >  block/blk-settings.c         |  5 ++---
> > > > >  block/blk-sysfs.c            |  1 -
> > > > >  block/genhd.c                | 13 +++++++++++--
> > > > >  drivers/block/aoe/aoeblk.c   |  2 --
> > > > >  drivers/block/drbd/drbd_nl.c | 12 +-----------
> > > > >  drivers/md/bcache/super.c    |  4 ----
> > > > >  drivers/md/dm-table.c        |  3 ---
> > > > >  drivers/md/raid0.c           | 16 ----------------
> > > > >  drivers/md/raid10.c          | 24 +-----------------------
> > > > >  drivers/md/raid5.c           | 13 +------------
> > > > >  10 files changed, 16 insertions(+), 77 deletions(-)
> > > > 
> > > > 
> > > > In general these changes need a solid audit relative to stacking
> > > > drivers.  That is, the limits stacking methods (blk_stack_limits)
> > > > vs lower level allocation methods (__device_add_disk).
> > > > 
> > > > You optimized for lowlevel __device_add_disk establishing the bdi's
> > > > ra_pages and io_pages.  That is at the beginning of disk allocation,
> > > > well before any build up of stacking driver's queue_io_opt() -- which
> > > > was previously done in disk_stack_limits or driver specific methods
> > > > (e.g. dm_table_set_restrictions) that are called _after_ all the limits
> > > > stacking occurs.
> > > > 
> > > > By inverting the setting of the bdi's ra_pages and io_pages to be done
> > > > so early in __device_add_disk it'll break properly setting these values
> > > > for at least DM afaict.
> > > 
> > > ra_pages never got inherited by stacking drivers, check it by modifying
> > > it on an underlying device and then creating a trivial dm or md one.
> > 
> > Sure, not saying that it did.  But if the goal is to set ra_pages based
> > on io_opt then to do that correctly on stacking drivers it must be done
> > in terms of limits stacking right?  Or at least done at a location that
> > is after the limits stacking has occurred?  So should DM just open-code
> > setting ra_pages like it did for io_pages?
> > 
> > Because setting ra_pages in __device_add_disk() is way too early for DM
> > -- given it uses device_add_disk_no_queue_reg via add_disk_no_queue_reg
> > at DM device creation (before stacking all underlying devices' limits).
> 
> I'll move it to blk_register_queue, which should work just fine.

That'll work for initial DM table load as part of DM device creation
(dm_setup_md_queue).  But it won't account for DM table reloads that
might change underlying devices on a live DM device (done using
__bind).

Both dm_setup_md_queue() and __bind() call dm_table_set_restrictions()
to set/update queue_limits.  It feels like __bind() will need to call a
new block helper to set/update parts of queue_limits (e.g. ra_pages and
io_pages).

Any chance you're open to factoring out that block function as an
exported symbol for use by blk_register_queue() and code like DM's
__bind()?

Thanks,
Mike


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Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-26 15:03 bdi cleanups v3 Christoph Hellwig
2020-07-26 15:03 ` [PATCH 01/14] fs: remove the unused SB_I_MULTIROOT flag Christoph Hellwig
2020-07-26 15:03 ` [PATCH 02/14] drbd: remove dead code in device_to_statistics Christoph Hellwig
2020-07-26 15:03 ` [PATCH 03/14] drbd: remove RB_CONGESTED_REMOTE Christoph Hellwig
2020-07-26 15:03 ` [PATCH 04/14] bdi: initialize ->ra_pages in bdi_init Christoph Hellwig
2020-07-26 15:03 ` [PATCH 05/14] md: update the optimal I/O size on reshape Christoph Hellwig
2020-07-26 15:03 ` [PATCH 06/14] block: lift setting the readahead size into the block layer Christoph Hellwig
2020-08-26 22:07   ` Mike Snitzer
2020-09-02 15:11     ` Christoph Hellwig
2020-09-02 16:20       ` Mike Snitzer
2020-09-10  9:28         ` Christoph Hellwig
2020-09-10 17:15           ` Mike Snitzer [this message]
2020-09-15  7:05             ` Christoph Hellwig
2020-07-26 15:03 ` [PATCH 07/14] block: make QUEUE_SYSFS_BIT_FNS a little more useful Christoph Hellwig
2020-07-29  8:57   ` [block] 54529aac98: fsmark.files_per_sec -13.6% regression kernel test robot
2020-07-30  2:14   ` [block] 54529aac98: blktests.block.005.fail kernel test robot
2020-07-26 15:03 ` [PATCH 08/14] block: add helper macros for queue sysfs entries Christoph Hellwig
2020-07-26 15:03 ` [PATCH 09/14] bdi: remove BDI_CAP_CGROUP_WRITEBACK Christoph Hellwig
2020-07-26 15:03 ` [PATCH 10/14] bdi: remove BDI_CAP_SYNCHRONOUS_IO Christoph Hellwig
2020-07-26 19:06   ` Minchan Kim
2020-07-27  7:58     ` Christoph Hellwig
2020-07-26 15:03 ` [PATCH 11/14] mm: use SWP_SYNCHRONOUS_IO more intelligently Christoph Hellwig
2020-07-26 15:03 ` [PATCH 12/14] bdi: replace BDI_CAP_STABLE_WRITES with a queue and a sb flag Christoph Hellwig
2020-07-26 15:03 ` [PATCH 13/14] bdi: invert BDI_CAP_NO_ACCT_WB Christoph Hellwig
2020-07-26 15:03 ` [PATCH 14/14] bdi: replace BDI_CAP_NO_{WRITEBACK, ACCT_DIRTY} with a single flag Christoph Hellwig
2020-07-26 15:12 ` bdi cleanups v3 Christoph Hellwig
  -- strict thread matches above, loose matches on Subject: below --
2020-07-24  7:32 Christoph Hellwig
2020-07-24  7:33 ` [PATCH 06/14] block: lift setting the readahead size into the block layer Christoph Hellwig
2020-07-28 12:23   ` Johannes Thumshirn
2020-07-22  6:25 bdi cleanups v2 Christoph Hellwig
2020-07-22  6:25 ` [PATCH 06/14] block: lift setting the readahead size into the block layer Christoph Hellwig
2020-07-22  7:13   ` Johannes Thumshirn
2020-07-22  7:18     ` Christoph Hellwig
2020-07-20  7:51 bdi cleanups Christoph Hellwig
2020-07-20  7:51 ` [PATCH 06/14] block: lift setting the readahead size into the block layer Christoph Hellwig

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