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

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Date:   Wed, 9 Dec 2020 12:01:27 +0000
From:   Pavel Begunkov <asml.silence@...il.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     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 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?

> 
>> +	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.

Agree. In the end I want to merge that into bio_iov_iter_get_pages().

-- 
Pavel Begunkov