From: Nicolas Pitre <nico@fluxnic.net>
To: Ira Weiny <ira.weiny@intel.com>
Cc: "Fabio M. De Francesco" <fmdefrancesco@gmail.com>,
Christian Brauner <brauner@kernel.org>,
linux-kernel@vger.kernel.org, bpf@vger.kernel.org,
"Venkataramanan, Anirudh" <anirudh.venkataramanan@intel.com>
Subject: Re: [PATCH] fs/cramfs: Convert kmap() to kmap_local_data()
Date: Sat, 31 Dec 2022 15:55:17 -0500 (EST) [thread overview]
Message-ID: <210n4959-p557-894p-20qp-r595540r0827@syhkavp.arg> (raw)
In-Reply-To: <Y69mtbmmbDcXhiln@iweiny-desk3>
[-- Attachment #1: Type: text/plain, Size: 1548 bytes --]
On Fri, 30 Dec 2022, Ira Weiny wrote:
> On Wed, Oct 12, 2022 at 11:13:56AM +0200, Fabio M. De Francesco wrote:
> > The use of kmap() is being deprecated in favor of kmap_local_page().
> >
> > There are two main problems with kmap(): (1) It comes with an overhead as
> > the mapping space is restricted and protected by a global lock for
> > synchronization and (2) it also requires global TLB invalidation when the
> > kmap’s pool wraps and it might block when the mapping space is fully
> > utilized until a slot becomes available.
> >
> > With kmap_local_page() the mappings are per thread, CPU local, can take
> > page faults, and can be called from any context (including interrupts).
> > It is faster than kmap() in kernels with HIGHMEM enabled. Furthermore,
> > the tasks can be preempted and, when they are scheduled to run again, the
> > kernel virtual addresses are restored and still valid.
> >
> > Since its use in fs/cramfs is safe everywhere, it should be preferred.
> >
> > Therefore, replace kmap() with kmap_local_page() in fs/cramfs. Instead
> > of open-coding kmap_local_page() + memcpy(), use memcpy_from_page().
> >
> > Cc: "Venkataramanan, Anirudh" <anirudh.venkataramanan@intel.com>
> > Suggested-by: Ira Weiny <ira.weiny@intel.com>
>
> Nicolas, I was auditing the kmap conversion status and I see you reviewed this
> but did not merge it. Are you still the maintainer for fs/cramfs? Should
> Fabio send this to someone else?
Please send it to Al Viro with my reviewed-by.
Nicolas
prev parent reply other threads:[~2022-12-31 20:59 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-12 9:13 [PATCH] fs/cramfs: Convert kmap() to kmap_local_data() Fabio M. De Francesco
2022-10-12 18:54 ` Nicolas Pitre
2022-10-17 6:35 ` Christian Brauner
2022-12-30 22:31 ` Ira Weiny
2022-12-31 20:55 ` Nicolas Pitre [this message]
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