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From: Christoph Hellwig <hch@infradead.org>
To: Ming Mao <maoming.maoming@huawei.com>
Cc: 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,
	willy@infradead.org, jhubbard@nvidia.com
Subject: Re: [PATCH V4 1/2] vfio dma_map/unmap: optimized for hugetlbfs pages
Date: Wed, 9 Sep 2020 09:01:14 +0100	[thread overview]
Message-ID: <20200909080114.GA8321@infradead.org> (raw)
In-Reply-To: <20200908133204.1338-2-maoming.maoming@huawei.com>

I really don't think this approach is any good.  You workaround
a deficiency in the pin_user_pages API in one particular caller for
one particular use case.

I think you'd rather want either:

 (1) a FOLL_HUGEPAGE flag for the pin_user_pages API family that returns
     a single struct page for any kind of huge page, which would also
     benefit all kinds of other users rather than adding these kinds of
     hacks to vfio.
 (2) add a bvec version of the API that returns a variable size
     "extent"

I had started on (2) a while ago, and here is branch with my code (which
is broken and fails test, but might be a start):

http://git.infradead.org/users/hch/misc.git/shortlog/refs/heads/gup-bvec

But for now I wonder if (1) is the better start, which could still be
reused to (2) later.


  reply	other threads:[~2020-09-09  8:01 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-08 13:32 [PATCH V4 0/2] vfio: optimized for hugetlbf pages when dma map/unmap Ming Mao
2020-09-08 13:32 ` [PATCH V4 1/2] vfio dma_map/unmap: optimized for hugetlbfs pages Ming Mao
2020-09-09  8:01   ` Christoph Hellwig [this message]
2020-09-09 13:05     ` Jason Gunthorpe
2020-09-09 14:29       ` Christoph Hellwig
2020-09-09 15:00         ` Matthew Wilcox
2020-09-09 15:09         ` Jason Gunthorpe
2020-09-09 13:41     ` Matthew Wilcox
2020-09-09 17:04     ` Matthew Wilcox
2020-09-08 13:32 ` [PATCH V4 2/2] vfio: optimized for unpinning pages Ming Mao

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