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Date:   Wed, 9 Sep 2020 16:00:15 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     Christoph Hellwig <hch@infradead.org>
Cc:     Jason Gunthorpe <jgg@ziepe.ca>,
        Ming Mao <maoming.maoming@huawei.com>,
        linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
        linux-mm@kvack.org, alex.williamson@redhat.com,
        akpm@linux-foundation.org, cohuck@redhat.com,
        jianjay.zhou@huawei.com, weidong.huang@huawei.com,
        peterx@redhat.com, aarcange@redhat.com, wangyunjian@huawei.com,
        jhubbard@nvidia.com
Subject: Re: [PATCH V4 1/2] vfio dma_map/unmap: optimized for hugetlbfs pages
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On Wed, Sep 09, 2020 at 03:29:41PM +0100, Christoph Hellwig wrote:
> On Wed, Sep 09, 2020 at 10:05:18AM -0300, Jason Gunthorpe wrote:
> > How to use? The VMAs can have mixed page sizes so the caller would
> > have to somehow switch and call twice? Not sure this is faster.
> 
> We can find out the page size based on the page.  Right now it is
> rather cumbersome, but one of willys pending series has a nicer helper
> for that.

Actually already merged.  There's page_size() which went into 5.4, and
is the one you'd want to use (also page_shift() and compound_nr()).
The thp_* equivalents (merged in 5.9) compile away to nothing if you
don't have CONFIG_TRANSPARENT_HUGEPAGE enabled, but since there are
many ways of getting a compound page mapped into userspace, page_size()
is the helper to use for VFIO.