linux-ext4 - Re: [PATCH RFC PKS/PMEM 24/58] fs/freevxfs: Utilize new kmap

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Date:   Tue, 13 Oct 2020 12:25:44 +0100
From:   Christoph Hellwig <hch@...radead.org>
To:     ira.weiny@...el.com
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
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        Peter Zijlstra <peterz@...radead.org>,
        Christoph Hellwig <hch@...radead.org>, x86@...nel.org,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Fenghua Yu <fenghua.yu@...el.com>, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-nvdimm@...ts.01.org,
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Subject: Re: [PATCH RFC PKS/PMEM 24/58] fs/freevxfs: Utilize new kmap_thread()

> -	kaddr = kmap(pp);
> +	kaddr = kmap_thread(pp);
>  	memcpy(kaddr, vip->vii_immed.vi_immed + offset, PAGE_SIZE);
> -	kunmap(pp);
> +	kunmap_thread(pp);

You only Cced me on this particular patch, which means I have absolutely
no idea what kmap_thread and kunmap_thread actually do, and thus can't
provide an informed review.

That being said I think your life would be a lot easier if you add
helpers for the above code sequence and its counterpart that copies
to a potential hughmem page first, as that hides the implementation
details from most users.