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Date:   Tue, 13 Oct 2020 11:44:29 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     "Weiny, Ira" <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>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Nicolas Pitre <nico@...xnic.net>, X86 ML <x86@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Linux Doc Mailing List <linux-doc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>, linux-kselftest@...r.kernel.org,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
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Subject: Re: [PATCH RFC PKS/PMEM 33/58] fs/cramfs: Utilize new kmap_thread()

On Fri, Oct 9, 2020 at 12:52 PM <ira.weiny@...el.com> wrote:
>
> From: Ira Weiny <ira.weiny@...el.com>
>
> The kmap() calls in this FS are localized to a single thread.  To avoid
> the over head of global PKRS updates use the new kmap_thread() call.
>
> Cc: Nicolas Pitre <nico@...xnic.net>
> Signed-off-by: Ira Weiny <ira.weiny@...el.com>
> ---
>  fs/cramfs/inode.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/fs/cramfs/inode.c b/fs/cramfs/inode.c
> index 912308600d39..003c014a42ed 100644
> --- a/fs/cramfs/inode.c
> +++ b/fs/cramfs/inode.c
> @@ -247,8 +247,8 @@ static void *cramfs_blkdev_read(struct super_block *sb, unsigned int offset,
>                 struct page *page = pages[i];
>
>                 if (page) {
> -                       memcpy(data, kmap(page), PAGE_SIZE);
> -                       kunmap(page);
> +                       memcpy(data, kmap_thread(page), PAGE_SIZE);
> +                       kunmap_thread(page);

Why does this need a sleepable kmap? This looks like a textbook
kmap_atomic() use case.

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