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

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Date:   Tue, 6 Sep 2022 00:37:00 -0700
From:   John Hubbard <jhubbard@...dia.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     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 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().

$ git grep -nw bio_release_pages
block/bio.c:1474:               bio_release_pages(bio, true);
block/bio.c:1490:       bio_release_pages(bio, false);
block/blk-map.c:308:    bio_release_pages(bio, false);
block/blk-map.c:610:                    bio_release_pages(bio, bio_data_dir(bio) == READ);
block/fops.c:99:        bio_release_pages(&bio, should_dirty);
block/fops.c:165:               bio_release_pages(bio, false);
block/fops.c:289:               bio_release_pages(bio, false);
fs/direct-io.c:510:             bio_release_pages(bio, should_dirty);
fs/iomap/direct-io.c:185:               bio_release_pages(bio, false);
fs/zonefs/super.c:793:  bio_release_pages(bio, false);


And these can probably be done in groups, not as one big patch--your
other email also asked to break them up into block, iomap, and legacy.

That would be nice, I really hate the ugly dio_w*() wrappers, thanks
for this help. :)

thanks,

-- 
John Hubbard
NVIDIA