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From: Christoph Hellwig <hch-jcswGhMUV9g@public.gmane.org>
To: Minchan Kim <minchan-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
Cc: Christoph Hellwig <hch-jcswGhMUV9g@public.gmane.org>,
	Jens Axboe <axboe-tSWWG44O7X1aa/9Udqfwiw@public.gmane.org>,
	Song Liu <song-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
	Hans de Goede <hdegoede-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
	Richard Weinberger <richard-/L3Ra7n9ekc@public.gmane.org>,
	linux-mtd-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org,
	dm-devel-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org,
	linux-block-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	drbd-dev-cunTk1MwBs8qoQakbn7OcQ@public.gmane.org,
	linux-raid-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org,
	cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
Subject: Re: [PATCH 10/14] bdi: remove BDI_CAP_SYNCHRONOUS_IO
Date: Mon, 27 Jul 2020 09:58:22 +0200	[thread overview]
Message-ID: <20200727075822.GA5355@lst.de> (raw)
In-Reply-To: <20200726190639.GA560221-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>

On Sun, Jul 26, 2020 at 12:06:39PM -0700, Minchan Kim wrote:
> > @@ -528,8 +530,7 @@ static ssize_t backing_dev_store(struct device *dev,
> >  	 * freely but in fact, IO is going on so finally could cause
> >  	 * use-after-free when the IO is really done.
> >  	 */
> > -	zram->disk->queue->backing_dev_info->capabilities &=
> > -			~BDI_CAP_SYNCHRONOUS_IO;
> > +	zram->disk->fops = &zram_wb_devops;
> >  	up_write(&zram->init_lock);
> 
> For zram, regardless of BDI_CAP_SYNCHRONOUS_IO, it have used rw_page
> every time on read/write path. This one with next patch will make zram
> use bio instead of rw_page when it's declared !BDI_CAP_SYNCHRONOUS_IO,
> which introduce regression for performance.

It really should not matter, as the overhead of setting up a bio
is minimal.  It also is only used in the legacy mpage buffered I/O
code outside of the swap code, which has so many performance issues on
its own that even if this made a difference it wouldn't matter.

If you want magic treatment for your zram swap code you really need
to integrate it with the swap code instead of burding the block layer
with all this mess.

WARNING: multiple messages have this Message-ID
From: Christoph Hellwig <hch@lst.de>
To: Minchan Kim <minchan@kernel.org>
Cc: Christoph Hellwig <hch@lst.de>, Jens Axboe <axboe@kernel.dk>,
	Song Liu <song@kernel.org>, Hans de Goede <hdegoede@redhat.com>,
	Richard Weinberger <richard@nod.at>,
	linux-mtd@lists.infradead.org, dm-devel@redhat.com,
	linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
	drbd-dev@lists.linbit.com, linux-raid@vger.kernel.org,
	linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
	cgroups@vger.kernel.org
Subject: Re: [PATCH 10/14] bdi: remove BDI_CAP_SYNCHRONOUS_IO
Date: Mon, 27 Jul 2020 09:58:22 +0200	[thread overview]
Message-ID: <20200727075822.GA5355@lst.de> (raw)
In-Reply-To: <20200726190639.GA560221@google.com>

On Sun, Jul 26, 2020 at 12:06:39PM -0700, Minchan Kim wrote:
> > @@ -528,8 +530,7 @@ static ssize_t backing_dev_store(struct device *dev,
> >  	 * freely but in fact, IO is going on so finally could cause
> >  	 * use-after-free when the IO is really done.
> >  	 */
> > -	zram->disk->queue->backing_dev_info->capabilities &=
> > -			~BDI_CAP_SYNCHRONOUS_IO;
> > +	zram->disk->fops = &zram_wb_devops;
> >  	up_write(&zram->init_lock);
> 
> For zram, regardless of BDI_CAP_SYNCHRONOUS_IO, it have used rw_page
> every time on read/write path. This one with next patch will make zram
> use bio instead of rw_page when it's declared !BDI_CAP_SYNCHRONOUS_IO,
> which introduce regression for performance.

It really should not matter, as the overhead of setting up a bio
is minimal.  It also is only used in the legacy mpage buffered I/O
code outside of the swap code, which has so many performance issues on
its own that even if this made a difference it wouldn't matter.

If you want magic treatment for your zram swap code you really need
to integrate it with the swap code instead of burding the block layer
with all this mess.

WARNING: multiple messages have this Message-ID
From: Christoph Hellwig <hch@lst.de>
To: Minchan Kim <minchan@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>,
	linux-raid@vger.kernel.org, Hans de Goede <hdegoede@redhat.com>,
	Richard Weinberger <richard@nod.at>,
	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-mm@kvack.org, linux-fsdevel@vger.kernel.org,
	cgroups@vger.kernel.org, Christoph Hellwig <hch@lst.de>,
	drbd-dev@lists.linbit.com
Subject: Re: [PATCH 10/14] bdi: remove BDI_CAP_SYNCHRONOUS_IO
Date: Mon, 27 Jul 2020 09:58:22 +0200	[thread overview]
Message-ID: <20200727075822.GA5355@lst.de> (raw)
In-Reply-To: <20200726190639.GA560221@google.com>

On Sun, Jul 26, 2020 at 12:06:39PM -0700, Minchan Kim wrote:
> > @@ -528,8 +530,7 @@ static ssize_t backing_dev_store(struct device *dev,
> >  	 * freely but in fact, IO is going on so finally could cause
> >  	 * use-after-free when the IO is really done.
> >  	 */
> > -	zram->disk->queue->backing_dev_info->capabilities &=
> > -			~BDI_CAP_SYNCHRONOUS_IO;
> > +	zram->disk->fops = &zram_wb_devops;
> >  	up_write(&zram->init_lock);
> 
> For zram, regardless of BDI_CAP_SYNCHRONOUS_IO, it have used rw_page
> every time on read/write path. This one with next patch will make zram
> use bio instead of rw_page when it's declared !BDI_CAP_SYNCHRONOUS_IO,
> which introduce regression for performance.

It really should not matter, as the overhead of setting up a bio
is minimal.  It also is only used in the legacy mpage buffered I/O
code outside of the swap code, which has so many performance issues on
its own that even if this made a difference it wouldn't matter.

If you want magic treatment for your zram swap code you really need
to integrate it with the swap code instead of burding the block layer
with all this mess.

______________________________________________________
Linux MTD discussion mailing list
http://lists.infradead.org/mailman/listinfo/linux-mtd/

  parent reply	other threads:[~2020-07-27  7:58 UTC|newest]

Thread overview: 72+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-26 15:03 bdi cleanups v3 Christoph Hellwig
2020-07-26 15:03 ` 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   ` Christoph Hellwig
2020-07-26 15:03 ` [PATCH 03/14] drbd: remove RB_CONGESTED_REMOTE Christoph Hellwig
2020-07-26 15:03   ` Christoph Hellwig
     [not found] ` <20200726150333.305527-1-hch-jcswGhMUV9g@public.gmane.org>
2020-07-26 15:03   ` [PATCH 02/14] drbd: remove dead code in device_to_statistics Christoph Hellwig
2020-07-26 15:03     ` Christoph Hellwig
2020-07-26 15:03     ` Christoph Hellwig
2020-07-26 15:03   ` [PATCH 04/14] bdi: initialize ->ra_pages in bdi_init Christoph Hellwig
2020-07-26 15:03     ` Christoph Hellwig
2020-07-26 15:03     ` 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     ` Christoph Hellwig
2020-07-26 15:03     ` Christoph Hellwig
2020-07-26 15:03   ` [PATCH 06/14] block: lift setting the readahead size into the block layer Christoph Hellwig
2020-07-26 15:03     ` Christoph Hellwig
2020-07-26 15:03     ` Christoph Hellwig
2020-08-26 22:07     ` Mike Snitzer
2020-08-26 22:07       ` Mike Snitzer
2020-09-02 15:11       ` Christoph Hellwig
2020-09-02 15:11         ` Christoph Hellwig
2020-09-02 15:11         ` Christoph Hellwig
2020-09-02 16:20         ` Mike Snitzer
2020-09-02 16:20           ` Mike Snitzer
2020-09-10  9:28           ` Christoph Hellwig
2020-09-10  9:28             ` Christoph Hellwig
2020-09-10  9:28             ` Christoph Hellwig
2020-09-10 17:15             ` Mike Snitzer
2020-09-10 17:15               ` Mike Snitzer
2020-09-15  7:05               ` Christoph Hellwig
2020-09-15  7:05                 ` Christoph Hellwig
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
2020-07-26 15:03     ` Christoph Hellwig
2020-07-26 15:03     ` Christoph Hellwig
2020-07-29  8:57     ` [block] 54529aac98: fsmark.files_per_sec -13.6% regression kernel test robot
2020-07-29  8:57       ` kernel test robot
2020-07-30  2:14     ` [block] 54529aac98: blktests.block.005.fail kernel test robot
2020-07-30  2:14       ` 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     ` Christoph Hellwig
2020-07-26 15:03     ` Christoph Hellwig
2020-07-26 15:03   ` [PATCH 13/14] bdi: invert BDI_CAP_NO_ACCT_WB Christoph Hellwig
2020-07-26 15:03     ` Christoph Hellwig
2020-07-26 15:03     ` Christoph Hellwig
2020-07-26 15:03 ` [PATCH 09/14] bdi: remove BDI_CAP_CGROUP_WRITEBACK Christoph Hellwig
2020-07-26 15:03   ` Christoph Hellwig
2020-07-26 15:03 ` [PATCH 10/14] bdi: remove BDI_CAP_SYNCHRONOUS_IO Christoph Hellwig
2020-07-26 15:03   ` Christoph Hellwig
2020-07-26 19:06   ` Minchan Kim
2020-07-26 19:06     ` Minchan Kim
     [not found]     ` <20200726190639.GA560221-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
2020-07-27  7:58       ` Christoph Hellwig [this message]
2020-07-27  7:58         ` Christoph Hellwig
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   ` 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   ` 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 15:03   ` [PATCH 14/14] bdi: replace BDI_CAP_NO_{WRITEBACK, ACCT_DIRTY} " Christoph Hellwig
2020-07-26 15:12 ` bdi cleanups v3 Christoph Hellwig
2020-07-26 15:12   ` Christoph Hellwig
  -- strict thread matches above, loose matches on Subject: below --
2020-07-24  7:32 Christoph Hellwig
2020-07-24  7:33 ` [PATCH 10/14] bdi: remove BDI_CAP_SYNCHRONOUS_IO Christoph Hellwig
2020-07-24  7:33   ` Christoph Hellwig
2020-07-28 12:26   ` Johannes Thumshirn
2020-07-28 12:26     ` Johannes Thumshirn
2020-07-28 12:26     ` Johannes Thumshirn
2020-07-22  6:25 bdi cleanups v2 Christoph Hellwig
2020-07-22  6:25 ` [PATCH 10/14] bdi: remove BDI_CAP_SYNCHRONOUS_IO Christoph Hellwig
2020-07-22  6:25   ` Christoph Hellwig
2020-07-20  7:51 bdi cleanups Christoph Hellwig
2020-07-20  7:51 ` [PATCH 10/14] bdi: remove BDI_CAP_SYNCHRONOUS_IO Christoph Hellwig
2020-07-20  7:51   ` Christoph Hellwig

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