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Subject: Re: [PATCH v4 0/4] mm/gup: page unpining improvements
To:     Christoph Hellwig <hch@infradead.org>
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        linux-rdma@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>,
        Jason Gunthorpe <jgg@ziepe.ca>,
        Doug Ledford <dledford@redhat.com>,
        John Hubbard <jhubbard@nvidia.com>,
        Matthew Wilcox <willy@infradead.org>
References: <20210212130843.13865-1-joao.m.martins@oracle.com>
 <20210218072432.GA325423@infradead.org>
From:   Joao Martins <joao.m.martins@oracle.com>
Message-ID: <a5f7d591-f3aa-1a54-569c-bd1abcb99334@oracle.com>
Date:   Thu, 18 Feb 2021 15:33:39 +0000
In-Reply-To: <20210218072432.GA325423@infradead.org>
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On 2/18/21 7:24 AM, Christoph Hellwig wrote:
> On Fri, Feb 12, 2021 at 01:08:39PM +0000, Joao Martins wrote:
>> Hey,
>>
>> This series improves page unpinning, with an eye on improving MR
>> deregistration for big swaths of memory (which is bound by the page
>> unpining), particularly:
> 
> Can you also take a look at the (bdev and iomap) direct I/O code to
> make use of this?  It should really help there, with a much wieder use
> than RDMA.
> 
Perhaps by bdev and iomap direct I/O using this, you were thinking to replace
bio_release_pages() which operates on bvecs and hence releasing contiguous pages
in a bvec at once? e.g. something like from this:

        bio_for_each_segment_all(bvec, bio, iter_all) {
                if (mark_dirty && !PageCompound(bvec->bv_page))
                        set_page_dirty_lock(bvec->bv_page);
                put_page(bvec->bv_page);
        }

(...) to this instead:

	bio_for_each_bvec_all(bvec, bio, i)
		unpin_user_page_range_dirty_lock(bvec->bv_page,
			DIV_ROUND_UP(bvec->bv_len, PAGE_SIZE),
			mark_dirty && !PageCompound(bvec->bv_page));