It was reported that allocating pages for the write buffer in dm-crypt causes measurable overhead [1]. This patch changes dm-crypt to allocate compound pages if they are available. If not, we fall back to the mempool. [1] https://listman.redhat.com/archives/dm-devel/2023-February/053284.html Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx> --- drivers/md/dm-crypt.c | 48 +++++++++++++++++++++++++++++++++--------------- 1 file changed, 33 insertions(+), 15 deletions(-) Index: linux-2.6/drivers/md/dm-crypt.c =================================================================== --- linux-2.6.orig/drivers/md/dm-crypt.c 2023-02-16 20:40:15.000000000 +0100 +++ linux-2.6/drivers/md/dm-crypt.c 2023-02-16 21:56:34.000000000 +0100 @@ -1657,6 +1657,9 @@ static void crypt_free_buffer_pages(stru * 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 size) { @@ -1664,8 +1667,8 @@ static struct bio *crypt_alloc_buffer(st struct bio *clone; unsigned int nr_iovecs = (size + PAGE_SIZE - 1) >> PAGE_SHIFT; gfp_t gfp_mask = GFP_NOWAIT | __GFP_HIGHMEM; - unsigned i, len, remaining_size; - struct page *page; + unsigned remaining_size; + unsigned order = MAX_ORDER - 1; retry: if (unlikely(gfp_mask & __GFP_DIRECT_RECLAIM)) @@ -1678,20 +1681,34 @@ 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 */ @@ -1709,12 +1726,13 @@ 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); + 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); } }
