dm crypt: allocate compound pages if possible

It was reported that allocating pages for the write buffer in dm-crypt
causes measurable overhead [1].

Change dm-crypt to allocate compound pages if they are available. If
not, fall back to the mempool.

[1] https://listman.redhat.com/archives/dm-devel/2023-February/053284.html

Suggested-by: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>

diff --git a/drivers/md/dm-crypt.c b/drivers/md/dm-crypt.c
index 09e37ebf7cc89789021c9320aafcd4c9bfc596f2..dbf13bd1d2190461d0b71719717981e8290eb584 100644 (file)
--- a/drivers/md/dm-crypt.c
+++ b/drivers/md/dm-crypt.c
@@ -1661,6 +1661,9 @@ static void crypt_free_buffer_pages(struct crypt_config *cc, struct bio *clone);
  * In order to not degrade performance with excessive locking, we try
  * non-blocking allocations without a mutex first but on failure we fallback
  * to blocking allocations with a mutex.
+ *
+ * In order to reduce allocation overhead, we try to allocate compound pages in
+ * the first pass. If they are not available, we fall back to the mempool.
  */
 static struct bio *crypt_alloc_buffer(struct dm_crypt_io *io, unsigned int size)
 {
@@ -1668,8 +1671,8 @@ static struct bio *crypt_alloc_buffer(struct dm_crypt_io *io, unsigned int size)
        struct bio *clone;
        unsigned int nr_iovecs = (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
        gfp_t gfp_mask = GFP_NOWAIT | __GFP_HIGHMEM;
-       unsigned int i, len, remaining_size;
-       struct page *page;
+       unsigned int remaining_size;
+       unsigned int order = MAX_ORDER - 1;
 
 retry:
        if (unlikely(gfp_mask & __GFP_DIRECT_RECLAIM))
@@ -1682,19 +1685,34 @@ retry:
 
        remaining_size = size;
 
-       for (i = 0; i < nr_iovecs; i++) {
-               page = mempool_alloc(&cc->page_pool, gfp_mask);
-               if (!page) {
+       while (remaining_size) {
+               struct page *pages;
+               unsigned size_to_add;
+               unsigned remaining_order = __fls((remaining_size + PAGE_SIZE - 1) >> PAGE_SHIFT);
+               order = min(order, remaining_order);
+
+               while (order > 0) {
+                       pages = alloc_pages(gfp_mask
+                               | __GFP_NOMEMALLOC | __GFP_NORETRY | __GFP_NOWARN | __GFP_COMP,
+                               order);
+                       if (likely(pages != NULL))
+                               goto have_pages;
+                       order--;
+               }
+
+               pages = mempool_alloc(&cc->page_pool, gfp_mask);
+               if (!pages) {
                        crypt_free_buffer_pages(cc, clone);
                        bio_put(clone);
                        gfp_mask |= __GFP_DIRECT_RECLAIM;
+                       order = 0;
                        goto retry;
                }
 
-               len = (remaining_size > PAGE_SIZE) ? PAGE_SIZE : remaining_size;
-
-               __bio_add_page(clone, page, len, 0);
-               remaining_size -= len;
+have_pages:
+               size_to_add = min((unsigned)PAGE_SIZE << order, remaining_size);
+               __bio_add_page(clone, pages, size_to_add, 0);
+               remaining_size -= size_to_add;
        }
 
        /* Allocate space for integrity tags */
@@ -1712,12 +1730,15 @@ retry:
 
 static void crypt_free_buffer_pages(struct crypt_config *cc, struct bio *clone)
 {
-       struct bio_vec *bv;
-       struct bvec_iter_all iter_all;
+       struct folio_iter fi;
 
-       bio_for_each_segment_all(bv, clone, iter_all) {
-               BUG_ON(!bv->bv_page);
-               mempool_free(bv->bv_page, &cc->page_pool);
+       if (clone->bi_vcnt > 0) { /* bio_for_each_folio_all crashes with an empty bio */
+               bio_for_each_folio_all(fi, clone) {
+                       if (folio_test_large(fi.folio))
+                               folio_put(fi.folio);
+                       else
+                               mempool_free(&fi.folio->page, &cc->page_pool);
+               }
        }
 }