From: Alan Stern <stern@rowland.harvard.edu>
To: Ingo Rohloff <ingo.rohloff@lauterbach.com>
Cc: Greg KH <gregkh@linuxfoundation.org>,
balbi@kernel.org, linux-usb@vger.kernel.org
Subject: Re: [PATCH v2 1/1] usb: gadget: f_fs: Support zerocopy transfers via mmap.
Date: Tue, 8 Feb 2022 10:21:51 -0500 [thread overview]
Message-ID: <YgKKj46jN1zGyqYR@rowland.harvard.edu> (raw)
In-Reply-To: <20220208124817.3bd884ba@ingpc2>
On Tue, Feb 08, 2022 at 12:48:17PM +0100, Ingo Rohloff wrote:
> > > + atomic64_sub(amount, &ffs->mmap_mem_usage);
> >
> > Why not use a real lock instead of trying to do a fake one with this
> > atomic variable?
>
> I don't think there is a good reason using the "atomic" stuff:
> I think this code path anyway is not hit that often (only when you mmap or
> munmap buffers), so this should not have any noticeable impact on performance.
>
> I just took the code from "drivers/usb/core/devio.c",
> "usbfs_increase_memory_usage()".
> I am still convinced it is correct.
>
> You are of course right: You can easily use a lock here and this makes the
> intention of the code a lot clearer I guess.
>
> I will modify the patch accordingly.
If you also feel like making a similar change to the code in devio.c, it
would be welcome.
Alan Stern
prev parent reply other threads:[~2022-02-08 15:21 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-02 17:20 [PATCH v2 0/1] Zerocopy for USB Gadget FunctionFS Ingo Rohloff
2022-02-02 17:20 ` [PATCH v2 1/1] usb: gadget: f_fs: Support zerocopy transfers via mmap Ingo Rohloff
2022-02-08 10:44 ` Greg KH
2022-02-08 11:48 ` Ingo Rohloff
2022-02-08 15:21 ` Alan Stern [this message]
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