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Message-ID: <20201012164438.GA20115@casper.infradead.org>
Date: Mon, 12 Oct 2020 17:44:38 +0100
From: Matthew Wilcox <willy@...radead.org>
To: Dave Hansen <dave.hansen@...el.com>
Cc: Eric Biggers <ebiggers@...nel.org>,
Ira Weiny <ira.weiny@...el.com>,
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Subject: Re: [PATCH RFC PKS/PMEM 22/58] fs/f2fs: Utilize new kmap_thread()
On Mon, Oct 12, 2020 at 09:28:29AM -0700, Dave Hansen wrote:
> kmap_atomic() is always preferred over kmap()/kmap_thread().
> kmap_atomic() is _much_ more lightweight since its TLB invalidation is
> always CPU-local and never broadcast.
>
> So, basically, unless you *must* sleep while the mapping is in place,
> kmap_atomic() is preferred.
But kmap_atomic() disables preemption, so the _ideal_ interface would map
it only locally, then on preemption make it global. I don't even know
if that _can_ be done. But this email makes it seem like kmap_atomic()
has no downsides.
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