linux-kernel - Re: [PATCH v2 1/2] iov_iter: optimise iov_iter

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Message-ID: <20201120081429.GA30801@infradead.org>
Date:   Fri, 20 Nov 2020 08:14:29 +0000
From:   Christoph Hellwig <hch@...radead.org>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Pavel Begunkov <asml.silence@...il.com>,
        Ming Lei <ming.lei@...hat.com>, linux-fsdevel@...r.kernel.org,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Jens Axboe <axboe@...nel.dk>, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] iov_iter: optimise iov_iter_npages for bvec

On Fri, Nov 20, 2020 at 02:54:57AM +0000, Matthew Wilcox wrote:
> On Fri, Nov 20, 2020 at 02:25:08AM +0000, Pavel Begunkov wrote:
> > On 20/11/2020 02:22, Ming Lei wrote:
> > > iov_iter_npages(bvec) still can be improved a bit by the following way:
> > 
> > Yep, was doing exactly that, +a couple of other places that are in my way.
> 
> Are you optimising the right thing here?  Assuming you're looking at
> the one in do_blockdev_direct_IO(), wouldn't we be better off figuring
> out how to copy the bvecs directly from the iov_iter into the bio
> rather than calling dio_bio_add_page() for each page?

Which is most effectively done by stopping to to use *blockdev_direct_IO
and switching to iomap instead :)