linux-kernel - Re: [PATCH v6 11/34] iov_iter, block: Make bio structs pin pages rather than ref'ing if appropriate

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Message-ID: <Y8Zf+gooUKwAZC7J@infradead.org>
Date:   Tue, 17 Jan 2023 00:44:42 -0800
From:   Christoph Hellwig <hch@...radead.org>
To:     David Howells <dhowells@...hat.com>
Cc:     Christoph Hellwig <hch@...radead.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Jens Axboe <axboe@...nel.dk>, Jan Kara <jack@...e.cz>,
        Christoph Hellwig <hch@....de>,
        Matthew Wilcox <willy@...radead.org>,
        Logan Gunthorpe <logang@...tatee.com>,
        linux-block@...r.kernel.org, Jeff Layton <jlayton@...nel.org>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 11/34] iov_iter, block: Make bio structs pin pages
 rather than ref'ing if appropriate

On Tue, Jan 17, 2023 at 08:26:08AM +0000, David Howells wrote:
> Um... With these patches, BIO_PAGE_REFFED is set by default when the bio is
> initialised otherwise every user of struct bio that currently adds pages
> directly (assuming there are any) rather than going through
> bio_iov_iter_get_pages() will have to set the flag, hence the need to clear
> it.

I think we need to fix that (in the patch inverting the polarity) and
only set the flag where it is needed.

All eventually calls come from the direct I/O code in the block layer,
iomap, legacy generic and zonefs, and they release pages that came
from some form of hup.  So we can just set BIO_PAGE_REFFED in
bio_iov_iter_get_pages and dio_refill_pages.