Re: [PATCH v2 0/7] convert most filesystems to pin_user_pages_fast()

John Hubbard
2022-09-06T07:37:09Z

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