linux-kernel - Re: [PATCH v2 0/7] convert most filesystems to pin_user_pages

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Message-ID: <Yxb6x50XqTfxrqB1@infradead.org>
Date:   Tue, 6 Sep 2022 00:46:15 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     John Hubbard <jhubbard@...dia.com>
Cc:     Christoph Hellwig <hch@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jens Axboe <axboe@...nel.dk>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Miklos Szeredi <miklos@...redi.hu>,
        "Darrick J . Wong" <djwong@...nel.org>,
        Trond Myklebust <trond.myklebust@...merspace.com>,
        Anna Schumaker <anna@...nel.org>, Jan Kara <jack@...e.cz>,
        David Hildenbrand <david@...hat.com>,
        Logan Gunthorpe <logang@...tatee.com>,
        linux-block@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-xfs@...r.kernel.org, linux-nfs@...r.kernel.org,
        linux-mm@...ck.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 0/7] convert most filesystems to pin_user_pages_fast()

On Tue, Sep 06, 2022 at 12:37:00AM -0700, John Hubbard wrote:
> On 9/6/22 00:22, Christoph Hellwig wrote:
> > On Tue, Sep 06, 2022 at 12:10:54AM -0700, John Hubbard wrote:
> >> I would be delighted if that were somehow possible. Every time I think
> >> it's possible, it has fallen apart. The fact that bio_release_pages()
> >> will need to switch over from put_page() to unpin_user_page(), combined
> >> with the fact that there are a lot of callers that submit bios, has
> >> led me to the current approach.
> > 
> > We can (temporarily) pass the gup flag to bio_release_pages or even
> > better add a new bio_unpin_pages helper that undoes the pin side.
> > That is: don't try to reuse the old APIs, but ad new ones, just like
> > we do on the lower layers.
> 
> OK...so, to confirm: the idea is to convert these callsites (below) to
> call a new bio_unpin_pages() routine that does unpin_user_page().

Yeah.  And to stay symmetric also a new bio_iov_iter_pin_pages for
the pin side.