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 | 50 ++++++++++++++++++++++++++++++++++++++++++-------- 1 file changed, 42 insertions(+), 8 deletions(-) Index: linux-2.6/drivers/md/dm-crypt.c =================================================================== --- linux-2.6.orig/drivers/md/dm-crypt.c 2023-01-20 13:22:38.000000000 +0100 +++ linux-2.6/drivers/md/dm-crypt.c 2023-02-16 18:33:42.000000000 +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 +1667,9 @@ 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; + unsigned remaining_size; struct page *page; + unsigned order = MAX_ORDER - 1; retry: if (unlikely(gfp_mask & __GFP_DIRECT_RECLAIM)) @@ -1678,20 +1682,37 @@ retry: remaining_size = size; - for (i = 0; i < nr_iovecs; i++) { + while (remaining_size) { + unsigned o; + unsigned remaining_order = __fls((remaining_size + PAGE_SIZE - 1) >> PAGE_SHIFT); + order = min(order, remaining_order); + + while (order > 0) { + page = alloc_pages(gfp_mask + | __GFP_NOMEMALLOC | __GFP_NORETRY | __GFP_NOWARN, order); + if (likely(page != NULL)) + goto have_pages; + order--; + } + page = mempool_alloc(&cc->page_pool, gfp_mask); if (!page) { 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); +have_pages: + page->compound_order = order; - remaining_size -= len; + for (o = 0; o < 1U << order; o++) { + unsigned len = min((unsigned)PAGE_SIZE, remaining_size); + bio_add_page(clone, page, len, 0); + remaining_size -= len; + page++; + } } /* Allocate space for integrity tags */ @@ -1711,10 +1732,23 @@ static void crypt_free_buffer_pages(stru { struct bio_vec *bv; struct bvec_iter_all iter_all; + unsigned skip_entries = 0; bio_for_each_segment_all(bv, clone, iter_all) { - BUG_ON(!bv->bv_page); - mempool_free(bv->bv_page, &cc->page_pool); + unsigned order; + struct page *page = bv->bv_page; + BUG_ON(!page); + if (skip_entries) { + skip_entries--; + continue; + } + order = page->compound_order; + if (order) { + __free_pages(page, order); + skip_entries = (1U << order) - 1; + } else { + mempool_free(page, &cc->page_pool); + } } }
