linux-kernel - Re: [PATCH] char_dev: replace cdev

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Message-ID: <X/yUzVu04TyVuU/f@kroah.com>
Date:   Mon, 11 Jan 2021 19:11:25 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Christoph Hellwig <hch@....de>, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] char_dev: replace cdev_map with an xarray

On Mon, Jan 11, 2021 at 05:35:00PM +0000, Matthew Wilcox wrote:
> On Mon, Jan 11, 2021 at 06:05:13PM +0100, 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.
> 
> Thanks for doing this.  We could make it more efficient for chardevs
> that occupy 64 or more consecutive/aligned devices -- is it worth doing?

efficient in what way?  Space or faster lookup?

THis shouldn't be on a "fast" lookup path, so I doubt that's worth
optimizing for.  Space, maybe, for systems with thousands of scsi
devices, but usually they just stick to the block device, not a char
device from what I remember.

thanks,

greg k-h