On 7/16/24 07:08, Chenliang Li wrote:
Add support for checking and coalescing multi-hugepage-backed fixed
buffers. The coalescing optimizes both time and space consumption caused
by mapping and storing multi-hugepage fixed buffers.
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@xxxxxxxxxxx>
---
The series looks good apart from the comment below, I'll run some
tests this week, I think you sent something for liburing/test
+static bool io_try_coalesce_buffer(struct page ***pages, int *nr_pages,
+ struct io_imu_folio_data *data)
+{
+ 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);
+ /*
+ * 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;
+ }
+
+ if (nr_folios == 1) {
+ if (folio_page_idx(folio, page_array[i-1])
+ != data->nr_pages_mid - 1)
Code style, comparison (i.e. "!=") should be on the previous line
+ return false;
+
+ data->nr_pages_head = count;
+ } else if (count != data->nr_pages_mid) {
+ return false;
+ }
+
+ folio = page_folio(page_array[i]);
+ if (folio_size(folio) != (1UL << data->folio_shift) ||
+ folio_page_idx(folio, page_array[i]) != 0)
+ return false;
+
+ count = 1;
+ nr_folios++;
+ }
+ if (nr_folios == 1) {
+ if (folio_page_idx(folio, page_array[i-1])
+ != data->nr_pages_mid - 1)
That's too restrictive and would be a regression. We currently allow
registrations fully falling under a single huge page but not matching
the right side. E.g. for a [N; M) huge page, you're allowed to register
[N + 4KB, M - 4KB). We should just remove this check.
And same comment about code style.
+ return false;
+
+ data->nr_pages_head = count;
+ }
+
+ return io_do_coalesce_buffer(pages, nr_pages, data, nr_folios);
+}
+
--
Pavel Begunkov
