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Date:   Sat, 10 Oct 2020 01:39:54 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Eric Biggers <ebiggers@...nel.org>
Cc:     ira.weiny@...el.com, 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>, linux-aio@...ck.org,
        linux-efi@...r.kernel.org, kvm@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-mmc@...r.kernel.org,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        dri-devel@...ts.freedesktop.org, linux-mm@...ck.org,
        target-devel@...r.kernel.org, linux-mtd@...ts.infradead.org,
        linux-kselftest@...r.kernel.org, samba-technical@...ts.samba.org,
        ceph-devel@...r.kernel.org, drbd-dev@...ts.linbit.com,
        devel@...verdev.osuosl.org, linux-cifs@...r.kernel.org,
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        linux-nvdimm@...ts.01.org, linux-rdma@...r.kernel.org,
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        xen-devel@...ts.xenproject.org, linux-ext4@...r.kernel.org,
        Fenghua Yu <fenghua.yu@...el.com>, ecryptfs@...r.kernel.org,
        linux-um@...ts.infradead.org, intel-gfx@...ts.freedesktop.org,
        linux-erofs@...ts.ozlabs.org, reiserfs-devel@...r.kernel.org,
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        Jaegeuk Kim <jaegeuk@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        io-uring@...r.kernel.org, linux-nfs@...r.kernel.org,
        linux-ntfs-dev@...ts.sourceforge.net, netdev@...r.kernel.org,
        kexec@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net,
        linux-fsdevel@...r.kernel.org, bpf@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-btrfs@...r.kernel.org
Subject: Re: [PATCH RFC PKS/PMEM 22/58] fs/f2fs: Utilize new kmap_thread()

On Fri, Oct 09, 2020 at 02:34:34PM -0700, Eric Biggers wrote:
> On Fri, Oct 09, 2020 at 12:49:57PM -0700, ira.weiny@...el.com wrote:
> > 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.
> >
> > @@ -2410,12 +2410,12 @@ static inline struct page *f2fs_pagecache_get_page(
> >  
> >  static inline void f2fs_copy_page(struct page *src, struct page *dst)
> >  {
> > -	char *src_kaddr = kmap(src);
> > -	char *dst_kaddr = kmap(dst);
> > +	char *src_kaddr = kmap_thread(src);
> > +	char *dst_kaddr = kmap_thread(dst);
> >  
> >  	memcpy(dst_kaddr, src_kaddr, PAGE_SIZE);
> > -	kunmap(dst);
> > -	kunmap(src);
> > +	kunmap_thread(dst);
> > +	kunmap_thread(src);
> >  }
> 
> Wouldn't it make more sense to switch cases like this to kmap_atomic()?
> The pages are only mapped to do a memcpy(), then they're immediately unmapped.

Maybe you missed the earlier thread from Thomas trying to do something
similar for rather different reasons ...

https://lore.kernel.org/lkml/20200919091751.011116649@linutronix.de/

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