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Date:   Fri, 19 Aug 2022 16:45:05 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     Uladzislau Rezki <urezki@gmail.com>
Cc:     Thomas Gleixner <tglx@linutronix.de>,
        Ira Weiny <ira.weiny@intel.com>,
        "Fabio M. De Francesco" <fmdefrancesco@gmail.com>,
        Luis Chamberlain <mcgrof@kernel.org>,
        linux-fsdevel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [RFC] vmap_folio()
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On Fri, Aug 19, 2022 at 12:53:32PM +0200, Uladzislau Rezki wrote:
> Looks pretty straightforward. One thing though, if we can combine it
> together with vmap(), since it is a copy paste in some sense, say to
> have something __vmap() to reuse it in the vmap_folio() and vmap().
> 
> But that is just a thought.

Thanks for looking it over!

Combining it with vmap() or vm_map_ram() is tricky.  Today, we assume
that each struct page pointer refers to exactly PAGE_SIZE bytes, so if
somebody calls alloc_pages(GFP_COMPOUND, 4) and then passes the head
page to vmap(), only that one page gets mapped.  I don't know whether
any current callers depend on that behaviour.

Now that I look at the future customers of this, I think I erred in basing
this on vmap(), it looks like vm_map_ram() is preferred.  So I'll redo
based on vm_map_ram().