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Date:   Wed, 9 Dec 2020 08:40:05 +0000
From:   Christoph Hellwig <hch@infradead.org>
To:     Pavel Begunkov <asml.silence@gmail.com>
Cc:     Jens Axboe <axboe@kernel.dk>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        linux-fsdevel@vger.kernel.org, io-uring@vger.kernel.org,
        linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
        Matthew Wilcox <willy@infradead.org>,
        Johannes Weiner <hannes@cmpxchg.org>
Subject: Re: [PATCH 2/2] block: no-copy bvec for direct IO
Message-ID: <20201209084005.GC21968@infradead.org>
References: <cover.1607477897.git.asml.silence@gmail.com>
 <51905c4fcb222e14a1d5cb676364c1b4f177f582.1607477897.git.asml.silence@gmail.com>
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> +	/*
> +	 * In practice groups of pages tend to be accessed/reclaimed/refaulted
> +	 * together. To not go over bvec for those who didn't set BIO_WORKINGSET
> +	 * approximate it by looking at the first page and inducing it to the
> +	 * whole bio
> +	 */
> +	if (unlikely(PageWorkingset(iter->bvec->bv_page)))
> +		bio_set_flag(bio, BIO_WORKINGSET);

IIRC the feedback was that we do not need to deal with BIO_WORKINGSET
at all for direct I/O.

> +	bio_set_flag(bio, BIO_NO_PAGE_REF);
> +
> +	iter->count = 0;
> +	return 0;
> +}

This helper should go into bio.c, next to bio_iov_iter_get_pages.
And please convert the other callers of bio_iov_iter_get_pages to this
scheme as well.