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Subject: Re: [PATCH v5 1/3] io_uring/rsrc: add hugepage fixed buffer coalesce
helpers
To: Chenliang Li <cliang01.li@samsung.com>, axboe@kernel.dk
Cc: io-uring@vger.kernel.org, peiwei.li@samsung.com, joshi.k@samsung.com,
kundan.kumar@samsung.com, anuj20.g@samsung.com, gost.dev@samsung.com
References: <20240628084411.2371-1-cliang01.li@samsung.com>
<CGME20240628084420epcas5p32f49e7c977695d20bcef7734eb2e38b4@epcas5p3.samsung.com>
<20240628084411.2371-2-cliang01.li@samsung.com>
Content-Language: en-US
From: Pavel Begunkov <asml.silence@gmail.com>
In-Reply-To: <20240628084411.2371-2-cliang01.li@samsung.com>
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On 6/28/24 09:44, Chenliang Li wrote:
> Introduce helper functions to check and coalesce hugepage-backed fixed
> buffers. The coalescing optimizes both time and space consumption caused
> by mapping and storing multi-hugepage fixed buffers. Currently we only
> have single-hugepage buffer coalescing, so add support for multi-hugepage
> fixed buffer coalescing.
>
> A coalescable multi-hugepage buffer should fully cover its folios
> (except potentially the first and last one), and these folios should
> have the same size. These requirements are for easier processing later,
> also we need same size'd chunks in io_import_fixed for fast iov_iter
> adjust.
>
> Signed-off-by: Chenliang Li <cliang01.li@samsung.com>
> ---
> io_uring/rsrc.c | 87 +++++++++++++++++++++++++++++++++++++++++++++++++
> io_uring/rsrc.h | 9 +++++
> 2 files changed, 96 insertions(+)
>
> diff --git a/io_uring/rsrc.c b/io_uring/rsrc.c
> index 60c00144471a..c88ce8c38515 100644
> --- a/io_uring/rsrc.c
> +++ b/io_uring/rsrc.c
> @@ -849,6 +849,93 @@ static int io_buffer_account_pin(struct io_ring_ctx *ctx, struct page **pages,
> return ret;
> }
>
> +static bool io_do_coalesce_buffer(struct page ***pages, int *nr_pages,
> + struct io_imu_folio_data *data, int nr_folios)
> +{
> + struct page **page_array = *pages, **new_array = NULL;
> + int nr_pages_left = *nr_pages, i, j;
> +
> + /* Store head pages only*/
> + new_array = kvmalloc_array(nr_folios, sizeof(struct page *),
> + GFP_KERNEL);
> + if (!new_array)
> + return false;
> +
> + new_array[0] = page_array[0];
> + /*
> + * The pages are bound to the folio, it doesn't
> + * actually unpin them but drops all but one reference,
> + * which is usually put down by io_buffer_unmap().
> + * Note, needs a better helper.
> + */
> + if (data->nr_pages_head > 1)
> + unpin_user_pages(&page_array[1], data->nr_pages_head - 1);
> +
> + j = data->nr_pages_head;
> + nr_pages_left -= data->nr_pages_head;
> + for (i = 1; i < nr_folios; i++) {
> + unsigned int nr_unpin;
> +
> + new_array[i] = page_array[j];
> + nr_unpin = min_t(unsigned int, nr_pages_left - 1,
> + data->nr_pages_mid - 1);
> + if (nr_unpin)
> + unpin_user_pages(&page_array[j+1], nr_unpin);
> + j += data->nr_pages_mid;
> + nr_pages_left -= data->nr_pages_mid;
> + }
> + kvfree(page_array);
> + *pages = new_array;
> + *nr_pages = nr_folios;
> + return true;
> +}
> +
> +static bool io_try_coalesce_buffer(struct page ***pages, int *nr_pages,
> + struct io_imu_folio_data *data)
I believe unused static function will trigger a warning, we don't
want that, especially since error on warn is a thing.
You can either reshuffle patches or at least add a
__maybe_unused attribute.
> +{
> + struct page **page_array = *pages;
> + struct folio *folio = page_folio(page_array[0]);
> + unsigned int count = 1, nr_folios = 1;
> + int i;
> +
> + if (*nr_pages <= 1)
> + return false;
> +
> + data->nr_pages_mid = folio_nr_pages(folio);
> + if (data->nr_pages_mid == 1)
> + return false;
> +
> + data->folio_shift = folio_shift(folio);
> + data->folio_size = folio_size(folio);
> + /*
> + * Check if pages are contiguous inside a folio, and all folios have
> + * the same page count except for the head and tail.
> + */
> + for (i = 1; i < *nr_pages; i++) {
> + if (page_folio(page_array[i]) == folio &&
> + page_array[i] == page_array[i-1] + 1) {
> + count++;
> + continue;
> + }
Seems like the first and last folios can be not border aligned,
i.e. the first should end at the folio_size boundary, and the
last one should start at the beginning of the folio.
Not really a bug, but we might get some problems with optimising
calculations down the road if we don't restrict it.
> +
> + if (nr_folios == 1)
> + data->nr_pages_head = count;
> + else if (count != data->nr_pages_mid)
> + return false;
> +
> + folio = page_folio(page_array[i]);
> + if (folio_size(folio) != data->folio_size)
> + return false;
> +
> + count = 1;
> + nr_folios++;
> + }
> + if (nr_folios == 1)
> + data->nr_pages_head = count;
> +
> + return io_do_coalesce_buffer(pages, nr_pages, data, nr_folios);
> +}
> +
> static int io_sqe_buffer_register(struct io_ring_ctx *ctx, struct iovec *iov,
> struct io_mapped_ubuf **pimu,
> struct page **last_hpage)
> diff --git a/io_uring/rsrc.h b/io_uring/rsrc.h
> index c032ca3436ca..cc66323535f6 100644
> --- a/io_uring/rsrc.h
> +++ b/io_uring/rsrc.h
> @@ -50,6 +50,15 @@ struct io_mapped_ubuf {
> struct bio_vec bvec[] __counted_by(nr_bvecs);
> };
>
> +struct io_imu_folio_data {
> + /* Head folio can be partially included in the fixed buf */
> + unsigned int nr_pages_head;
> + /* For non-head/tail folios, has to be fully included */
> + unsigned int nr_pages_mid;
> + unsigned int folio_shift;
> + size_t folio_size;
> +};
> +
> void io_rsrc_node_ref_zero(struct io_rsrc_node *node);
> void io_rsrc_node_destroy(struct io_ring_ctx *ctx, struct io_rsrc_node *ref_node);
> struct io_rsrc_node *io_rsrc_node_alloc(struct io_ring_ctx *ctx);
--
Pavel Begunkov