From: Matthew Wilcox <willy@infradead.org>
To: Pavel Begunkov <asml.silence@gmail.com>
Cc: Christoph Hellwig <hch@infradead.org>,
Ming Lei <ming.lei@redhat.com>,
linux-fsdevel@vger.kernel.org,
Alexander Viro <viro@zeniv.linux.org.uk>,
Jens Axboe <axboe@kernel.dk>,
linux-block@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 1/2] iov_iter: optimise iov_iter_npages for bvec
Date: Fri, 20 Nov 2020 13:13:52 +0000 [thread overview]
Message-ID: <20201120131352.GO29991@casper.infradead.org> (raw)
In-Reply-To: <c14607c3-2fdd-4acf-e379-a8cde461c753@gmail.com>
On Fri, Nov 20, 2020 at 01:00:37PM +0000, Pavel Begunkov wrote:
> On 20/11/2020 12:39, Matthew Wilcox wrote:
> > On Fri, Nov 20, 2020 at 08:14:29AM +0000, Christoph Hellwig wrote:
> >> 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 :)
> >
> > But iomap still calls iov_iter_npages(). So maybe we need something like
> > this ...
>
> Yep, all that are not mutually exclusive optimisations.
> Why `return 1`? It seems to be used later in bio_alloc(nr_pages)
because 0 means "no pages". It does no harm to allocate one biovec
that we then don't use.
> > - nr_pages = iov_iter_npages(dio->submit.iter, BIO_MAX_PAGES);
> > + nr_pages = bio_iov_iter_npages(dio->submit.iter);
> > if (nr_pages <= 0) {
^^^^^^^^^^^^^
> > - nr_pages = iov_iter_npages(dio->submit.iter, BIO_MAX_PAGES);
> > + nr_pages = bio_iov_iter_npages(dio->submit.iter);
> > iomap_dio_submit_bio(dio, iomap, bio, pos);
> > pos += n;
> > } while (nr_pages);
^^^^^^^^
next prev parent reply other threads:[~2020-11-20 13:14 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-19 23:24 [PATCH v2 0/2] optimise iov_iter Pavel Begunkov
2020-11-19 23:24 ` [PATCH v2 1/2] iov_iter: optimise iov_iter_npages for bvec Pavel Begunkov
2020-11-20 1:20 ` Matthew Wilcox
2020-11-20 1:39 ` Pavel Begunkov
2020-11-20 1:49 ` Matthew Wilcox
2020-11-20 1:56 ` Pavel Begunkov
2020-11-20 2:06 ` Matthew Wilcox
2020-11-20 2:08 ` Pavel Begunkov
2020-11-20 2:24 ` Ming Lei
2020-11-20 17:22 ` Pavel Begunkov
2020-11-20 17:23 ` Pavel Begunkov
2020-11-20 2:22 ` Ming Lei
2020-11-20 2:25 ` Pavel Begunkov
2020-11-20 2:54 ` Matthew Wilcox
2020-11-20 8:14 ` Christoph Hellwig
2020-11-20 12:39 ` Matthew Wilcox
2020-11-20 13:00 ` Pavel Begunkov
2020-11-20 13:13 ` Matthew Wilcox [this message]
2020-11-20 9:57 ` Pavel Begunkov
2020-11-20 13:29 ` David Laight
2020-11-19 23:24 ` [PATCH v2 2/2] iov_iter: optimise iter type checking Pavel Begunkov
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