linux-kernel - Re: [PATCH 2/2] block: no-copy bvec for direct IO

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Date:   Wed, 9 Dec 2020 12:05:31 +0000
From:   Christoph Hellwig <hch@...radead.org>
To:     Pavel Begunkov <asml.silence@...il.com>
Cc:     Christoph Hellwig <hch@...radead.org>,
        Jens Axboe <axboe@...nel.dk>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel@...r.kernel.org, io-uring@...r.kernel.org,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        Matthew Wilcox <willy@...radead.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Ming Lei <ming.lei@...hat.com>
Subject: Re: [PATCH 2/2] block: no-copy bvec for direct IO

On Wed, Dec 09, 2020 at 12:01:27PM +0000, Pavel Begunkov wrote:
> On 09/12/2020 08:40, Christoph Hellwig wrote:
> >> +	/*
> >> +	 * 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.
> 
> I was waiting for the conversation to unfold, i.e. for Johannes to
> answer. BTW, would the same (skipping BIO_WORKINGSET) stand true for
> iomap?

iomap direct I/O: yes.