linux-kernel - Re: [PATCH v7 4/8] block: Rename BIO_NO_PAGE_REF to BIO_PAGE

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Message-ID: <Y8vi8/sCvOxvLzzc@infradead.org>
Date:   Sat, 21 Jan 2023 05:04:51 -0800
From:   Christoph Hellwig <hch@...radead.org>
To:     David Howells <dhowells@...hat.com>
Cc:     Al Viro <viro@...iv.linux.org.uk>,
        Christoph Hellwig <hch@...radead.org>,
        Matthew Wilcox <willy@...radead.org>,
        Jens Axboe <axboe@...nel.dk>, Jan Kara <jack@...e.cz>,
        Jeff Layton <jlayton@...nel.org>,
        Logan Gunthorpe <logang@...tatee.com>,
        linux-fsdevel@...r.kernel.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v7 4/8] block: Rename BIO_NO_PAGE_REF to BIO_PAGE_REFFED
 and invert the meaning

On Fri, Jan 20, 2023 at 05:55:52PM +0000, David Howells wrote:
> Rename BIO_NO_PAGE_REF to BIO_PAGE_REFFED and invert the meaning.  In a
> following patch I intend to add a BIO_PAGE_PINNED flag to indicate that the
> page needs unpinning and this way both flags have the same logic.
> 
> Signed-off-by: David Howells <dhowells@...hat.com>
> Reviewed-by: Christoph Hellwig <hch@....de>

As pointed out last time, we really should not set the flag by default.
When a bio is allocated there are no pages to be released, that only
happens when we add dio-like pages to the bio.  Instead of explaining
why I mean again, I've put together a version of this series that
implements this and my other suggestions here:

http://git.infradead.org/users/hch/misc.git/shortlog/refs/heads/dio-pin-pages

This also tests fine with xfs and btrfs and nvme passthrough I/O.