Re: [PATCH v2 7/7] fuse: convert direct IO paths to use FOLL_PIN

John Hubbard
2022-09-01T01:34:05Z

On 8/31/22 03:37, Miklos Szeredi wrote:

Hi Miklos,

Thanks for looking at this, I'll accept all of these suggestions.

> On Wed, 31 Aug 2022 at 06:19, John Hubbard <jhubbard@nvidia.com> wrote:
>>
>> Convert the fuse filesystem to use pin_user_pages_fast() and
>> unpin_user_page(), instead of get_user_pages_fast() and put_page().
>>
>> The user of pin_user_pages_fast() depends upon:
>>
>> 1) CONFIG_BLK_USE_PIN_USER_PAGES_FOR_DIO, and
>>
>> 2) User-space-backed pages or ITER_BVEC pages.
>>
>> Signed-off-by: John Hubbard <jhubbard@nvidia.com>
>> ---
>> fs/fuse/dev.c | 11 +++++++++--
>> fs/fuse/file.c | 32 +++++++++++++++++++++-----------
>> fs/fuse/fuse_i.h | 1 +
>> 3 files changed, 31 insertions(+), 13 deletions(-)
>>
>> diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
>> index 51897427a534..5de98a7a45b1 100644
>> --- a/fs/fuse/dev.c
>> +++ b/fs/fuse/dev.c
>> @@ -675,7 +675,12 @@ static void fuse_copy_finish(struct fuse_copy_state *cs)
>> flush_dcache_page(cs->pg);
>> set_page_dirty_lock(cs->pg);
>> }
>> - put_page(cs->pg);
>> + if (!cs->pipebufs &&
>> + (user_backed_iter(cs->iter) || iov_iter_is_bvec(cs->iter)))
>> + dio_w_unpin_user_page(cs->pg);
>> +
>> + else
>> + put_page(cs->pg);
>
> Why not move the logic into a helper and pass a "bool pinned" argument?

OK, will do.

It's not yet clear from the discussion in the other thread with Jan and Al [1],
if I'll end up keeping this check:

user_backed_iter(cs->iter) || iov_iter_is_bvec(cs->iter)

...but if it stays, then the helper is a good idea.

>
>> }
>> cs->pg = NULL;
>> }
>> @@ -730,7 +735,9 @@ static int fuse_copy_fill(struct fuse_copy_state *cs)
>> }
>> } else {
>> size_t off;
>> - err = iov_iter_get_pages2(cs->iter, &page, PAGE_SIZE, 1, &off);
>> +
>> + err = dio_w_iov_iter_pin_pages(cs->iter, &page, PAGE_SIZE, 1,
>> + &off);
>> if (err < 0)
>> return err;
>> BUG_ON(!err);
>> diff --git a/fs/fuse/file.c b/fs/fuse/file.c
>> index 1a3afd469e3a..01da38928d0b 100644
>> --- a/fs/fuse/file.c
>> +++ b/fs/fuse/file.c
>> @@ -625,14 +625,19 @@ void fuse_read_args_fill(struct fuse_io_args *ia, struct file *file, loff_t pos,
>> }
>>
>> static void fuse_release_user_pages(struct fuse_args_pages *ap,
>> - bool should_dirty)
>> + bool should_dirty, bool is_user_or_bvec)
>> {
>> unsigned int i;
>>
>> - for (i = 0; i < ap->num_pages; i++) {
>> - if (should_dirty)
>> - set_page_dirty_lock(ap->pages[i]);
>> - put_page(ap->pages[i]);
>> + if (is_user_or_bvec) {
>> + dio_w_unpin_user_pages_dirty_lock(ap->pages, ap->num_pages,
>> + should_dirty);
>> + } else {
>> + for (i = 0; i < ap->num_pages; i++) {
>> + if (should_dirty)
>> + set_page_dirty_lock(ap->pages[i]);
>> + put_page(ap->pages[i]);
>> + }
>
> Same here.

Yes. Definitely belongs in a helper function. I was thinking, "don't
go that far, because the code will eventually get deleted anyway", but
you are right. :)

>
>> }
>> }
>>
>> @@ -733,7 +738,7 @@ static void fuse_aio_complete_req(struct fuse_mount *fm, struct fuse_args *args,
>> struct fuse_io_priv *io = ia->io;
>> ssize_t pos = -1;
>>
>> - fuse_release_user_pages(&ia->ap, io->should_dirty);
>> + fuse_release_user_pages(&ia->ap, io->should_dirty, io->is_user_or_bvec);
>>
>> if (err) {
>> /* Nothing */
>> @@ -1414,10 +1419,10 @@ static int fuse_get_user_pages(struct fuse_args_pages *ap, struct iov_iter *ii,
>> while (nbytes < *nbytesp && ap->num_pages < max_pages) {
>> unsigned npages;
>> size_t start;
>> - ret = iov_iter_get_pages2(ii, &ap->pages[ap->num_pages],
>> - *nbytesp - nbytes,
>> - max_pages - ap->num_pages,
>> - &start);
>> + ret = dio_w_iov_iter_pin_pages(ii, &ap->pages[ap->num_pages],
>> + *nbytesp - nbytes,
>> + max_pages - ap->num_pages,
>> + &start);
>> if (ret < 0)
>> break;
>>
>> @@ -1483,6 +1488,10 @@ ssize_t fuse_direct_io(struct fuse_io_priv *io, struct iov_iter *iter,
>> fl_owner_t owner = current->files;
>> size_t nbytes = min(count, nmax);
>>
>> + /* For use in fuse_release_user_pages(): */
>> + io->is_user_or_bvec = user_backed_iter(iter) ||
>> + iov_iter_is_bvec(iter);
>> +
>
> How about io->is_pinned? And a iov_iter_is_pinned() helper?

Agreed, is_pinned is a better name, and the helper (if we end up needing
that logic) also sounds good.

[1] https://lore.kernel.org/r/20220831094349.boln4jjajkdtykx3@quack3

thanks,

--
John Hubbard
NVIDIA