From: Christoph Hellwig <hch@lst.de>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Christoph Hellwig <hch@lst.de>, Jens Axboe <axboe@kernel.dk>,
"Rafael J. Wysocki" <rafael@kernel.org>,
Denis Efremov <efremov@linux.com>,
"David S. Miller" <davem@davemloft.net>,
Song Liu <song@kernel.org>, Al Viro <viro@zeniv.linux.org.uk>,
linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-ide@vger.kernel.org, linux-raid@vger.kernel.org,
linux-scsi@vger.kernel.org, linux-m68k@lists.linux-m68k.org
Subject: Re: [PATCH 01/19] char_dev: replace cdev_map with an xarray
Date: Thu, 27 Aug 2020 10:53:53 +0200 [thread overview]
Message-ID: <20200827085353.GA12111@lst.de> (raw)
In-Reply-To: <20200826081905.GB1796103@kroah.com>
On Wed, Aug 26, 2020 at 10:19:05AM +0200, Greg Kroah-Hartman wrote:
> On Wed, Aug 26, 2020 at 08:24:28AM +0200, Christoph Hellwig wrote:
> > None of the complicated overlapping regions bits of the kobj_map are
> > required for the character device lookup, so just a trivial xarray
> > instead.
> >
> > Signed-off-by: Christoph Hellwig <hch@lst.de>
>
> Really? This is ok to use and just as fast? If so, wonderful, it would
> be great to clean up kobj_map users.
Xarrays provide pretty efficient as long as we have a unsigned long
or smaller index (check, dev_t is small) and the indices are reasonable
clustered (check, minors for the same major). Memory usage will go down
vs the probes, and lookup speed up.
> > + mutex_lock(&chrdevs_lock);
> > + for (i = 0; i < count; i++) {
> > + error = xa_insert(&cdev_map, dev + i, p, GFP_KERNEL);
> > + if (error)
> > + goto out_unwind;
> > + }
> > + mutex_unlock(&chrdevs_lock);
> >
> > kobject_get(p->kobj.parent);
>
> Can't you drop this kobject_get() too?
I'll have to drop it or add back the put on the delete side. And
I think the latter is safer for now, because..
>
> And also the "struct kobj" in struct cdev can be gone as well, as the
> kobj_map was the only "real" user of this structure. I know some
> drivers liked to touch that field as well, but it never actually did
> anything for them, so it was pointless, but it will take some 'make
> allmodconfig' builds to flush them out.
I looked at it, but it does get registered and shows up in sysfs.
I don't really dare to touch this for now, as it can have huge
implications. Better done in a separate series (if we can actually do
it at all).
next prev parent reply other threads:[~2020-08-27 8:54 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-26 6:24 simplify gendisk lookup and remove struct block_device aliases Christoph Hellwig
2020-08-26 6:24 ` [PATCH 01/19] char_dev: replace cdev_map with an xarray Christoph Hellwig
2020-08-26 8:19 ` Greg Kroah-Hartman
2020-08-27 8:53 ` Christoph Hellwig [this message]
2020-08-27 9:18 ` Greg Kroah-Hartman
2020-08-27 9:39 ` Christoph Hellwig
2020-08-27 7:25 ` Hannes Reinecke
2020-08-27 8:55 ` Christoph Hellwig
2020-08-26 6:24 ` [PATCH 02/19] block: merge drivers/base/map.c into block/genhd.c Christoph Hellwig
2020-08-26 8:19 ` Greg Kroah-Hartman
2020-08-26 6:24 ` [PATCH 03/19] block: cleanup del_gendisk a bit Christoph Hellwig
2020-08-26 6:24 ` [PATCH 04/19] block: split block_class_lock Christoph Hellwig
2020-08-26 6:24 ` [PATCH 05/19] block: rework requesting modules for unclaimed devices Christoph Hellwig
2020-08-26 6:24 ` [PATCH 06/19] block: add an optional probe callback to major_names Christoph Hellwig
2020-08-26 6:24 ` [PATCH 07/19] ide: remove ide_{,un}register_region Christoph Hellwig
2020-08-27 7:25 ` Hannes Reinecke
2020-08-26 6:24 ` [PATCH 08/19] swim: don't call blk_register_region Christoph Hellwig
2020-08-26 6:24 ` [PATCH 09/19] sd: use __register_blkdev to avoid a modprobe for an unregistered dev_t Christoph Hellwig
2020-08-26 6:24 ` [PATCH 10/19] brd: use __register_blkdev to allocate devices on demand Christoph Hellwig
2020-08-26 6:24 ` [PATCH 11/19] loop: " Christoph Hellwig
2020-08-26 6:24 ` [PATCH 12/19] md: " Christoph Hellwig
2020-08-28 7:08 ` Song Liu
2020-08-26 6:24 ` [PATCH 13/19] ide: switch to __register_blkdev for command set probing Christoph Hellwig
2020-08-26 6:24 ` [PATCH 14/19] floppy: use a separate gendisk for each media format Christoph Hellwig
2020-08-26 6:24 ` [PATCH 15/19] amiflop: use separate gendisks for Amiga vs MS-DOS mode Christoph Hellwig
2020-08-26 6:24 ` [PATCH 16/19] ataflop: use a separate gendisk for each media format Christoph Hellwig
2020-08-26 6:24 ` [PATCH 17/19] z2ram: reindent Christoph Hellwig
2020-08-26 9:12 ` Joe Perches
2020-08-26 9:49 ` John Paul Adrian Glaubitz
2020-08-26 14:51 ` Joe Perches
2020-08-27 23:21 ` Finn Thain
2020-08-28 0:01 ` Joe Perches
2020-08-28 0:57 ` Finn Thain
2020-08-28 1:11 ` Joe Perches
2020-08-28 4:25 ` Christoph Hellwig
2020-08-26 6:24 ` [PATCH 18/19] z2ram: use separate gendisk for the different modes Christoph Hellwig
2020-08-26 6:24 ` [PATCH 19/19] block: switch gendisk lookup to a simple xarray Christoph Hellwig
-- strict thread matches above, loose matches on Subject: below --
2020-08-30 6:24 simplify gendisk lookup and remove struct block_device aliases v2 Christoph Hellwig
2020-08-30 6:24 ` [PATCH 01/19] char_dev: replace cdev_map with an xarray Christoph Hellwig
2020-08-30 7:31 ` Greg Kroah-Hartman
2020-09-03 8:01 simplify gendisk lookup and remove struct block_device aliases v3 Christoph Hellwig
2020-09-03 8:01 ` [PATCH 01/19] char_dev: replace cdev_map with an xarray Christoph Hellwig
2020-09-04 10:16 ` Hannes Reinecke
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