On 20/11/2020 12:39, Matthew Wilcox wrote:
> On Fri, Nov 20, 2020 at 08:14:29AM +0000, Christoph Hellwig wrote:
>> On Fri, Nov 20, 2020 at 02:54:57AM +0000, Matthew Wilcox wrote:
>>> On Fri, Nov 20, 2020 at 02:25:08AM +0000, Pavel Begunkov wrote:
>>>> On 20/11/2020 02:22, Ming Lei wrote:
>>>>> iov_iter_npages(bvec) still can be improved a bit by the following way:
>>>>
>>>> Yep, was doing exactly that, +a couple of other places that are in my way.
>>>
>>> Are you optimising the right thing here? Assuming you're looking at
>>> the one in do_blockdev_direct_IO(), wouldn't we be better off figuring
>>> out how to copy the bvecs directly from the iov_iter into the bio
>>> rather than calling dio_bio_add_page() for each page?
>>
>> Which is most effectively done by stopping to to use *blockdev_direct_IO
>> and switching to iomap instead :)
>
> But iomap still calls iov_iter_npages(). So maybe we need something like
> this ...
Yep, all that are not mutually exclusive optimisations.
Why `return 1`? It seems to be used later in bio_alloc(nr_pages)
>
> diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
> index 933f234d5bec..1c5a802a45d9 100644
> --- a/fs/iomap/direct-io.c
> +++ b/fs/iomap/direct-io.c
> @@ -250,7 +250,7 @@ iomap_dio_bio_actor(struct inode *inode, loff_t pos, loff_t length,
> orig_count = iov_iter_count(dio->submit.iter);
> iov_iter_truncate(dio->submit.iter, length);
>
> - nr_pages = iov_iter_npages(dio->submit.iter, BIO_MAX_PAGES);
> + nr_pages = bio_iov_iter_npages(dio->submit.iter);
> if (nr_pages <= 0) {
> ret = nr_pages;
> goto out;
> @@ -308,7 +308,7 @@ iomap_dio_bio_actor(struct inode *inode, loff_t pos, loff_t length,
> dio->size += n;
> copied += n;
>
> - nr_pages = iov_iter_npages(dio->submit.iter, BIO_MAX_PAGES);
> + nr_pages = bio_iov_iter_npages(dio->submit.iter);
> iomap_dio_submit_bio(dio, iomap, bio, pos);
> pos += n;
> } while (nr_pages);
> diff --git a/include/linux/bio.h b/include/linux/bio.h
> index c6d765382926..86cc74f84b30 100644
> --- a/include/linux/bio.h
> +++ b/include/linux/bio.h
> @@ -10,6 +10,7 @@
> #include <linux/ioprio.h>
> /* struct bio, bio_vec and BIO_* flags are defined in blk_types.h */
> #include <linux/blk_types.h>
> +#include <linux/uio.h>
>
> #define BIO_DEBUG
>
> @@ -447,6 +448,16 @@ bool __bio_try_merge_page(struct bio *bio, struct page *page,
> void __bio_add_page(struct bio *bio, struct page *page,
> unsigned int len, unsigned int off);
> int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter);
> +
> +static inline int bio_iov_iter_npages(const struct iov_iter *i)
> +{
> + if (!iov_iter_count(i))
> + return 0;
> + if (iov_iter_is_bvec(i))
> + return 1;
> + return iov_iter_npages(i, BIO_MAX_PAGES);
> +}
> +
> void bio_release_pages(struct bio *bio, bool mark_dirty);
> extern void bio_set_pages_dirty(struct bio *bio);
> extern void bio_check_pages_dirty(struct bio *bio);
>
--
Pavel Begunkov
