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

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Message-ID: <20201013205248.GJ2046448@iweiny-DESK2.sc.intel.com>
Date:   Tue, 13 Oct 2020 13:52:49 -0700
From:   Ira Weiny <ira.weiny@...el.com>
To:     Christoph Hellwig <hch@...radead.org>
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>, 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,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
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Subject: Re: [PATCH RFC PKS/PMEM 24/58] fs/freevxfs: Utilize new kmap_thread()

On Tue, Oct 13, 2020 at 12:25:44PM +0100, Christoph Hellwig wrote:
> > -	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.

Sorry the list was so big I struggled with who to CC and on which patches.

> 
> 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.

Matthew Wilcox and Al Viro have suggested similar ideas.

https://lore.kernel.org/lkml/20201013205012.GI2046448@iweiny-DESK2.sc.intel.com/

Ira