| Message ID | alpine.LRH.2.21.2302161245210.18393@file01.intranet.prod.int.rdu2.redhat.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | dm-crypt: allocate compound pages if possible | expand |
On Thu, Feb 16, 2023 at 12:47:08PM -0500, Mikulas Patocka wrote: > + while (order > 0) { > + page = alloc_pages(gfp_mask > + | __GFP_NOMEMALLOC | __GFP_NORETRY | __GFP_NOWARN, order); ... | __GFP_COMP > 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; No. You'll corrupt the next page if page is order-0, which it is if it came from the mempool. Also we've deleted page->compound_order in -next so you can't make this mistake. Using __GFP_COMP will set this field for you, so you can just drop this line. > - 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++; You can add multiple pages at once, whether they're compound or not. So replace this entire loop with: bio_add_page(clone, page, remaining_size, 0); > @@ -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); > + } You can simplify this by using the folio code. struct folio_iter fi; bio_for_each_folio_all(fi, bio) { if (folio_test_large(folio)) folio_put(folio); else mempool_free(&folio->page, &cc->page_pool); } (further work would actually convert this driver to use folios instead of pages)
On Thu, 16 Feb 2023, Matthew Wilcox wrote: > > - len = (remaining_size > PAGE_SIZE) ? PAGE_SIZE : remaining_size; > > - > > - bio_add_page(clone, page, len, 0); > > +have_pages: > > + page->compound_order = order; > > No. You'll corrupt the next page if page is order-0, which it is if it > came from the mempool. Also we've deleted page->compound_order in -next > so you can't make this mistake. Using __GFP_COMP will set this field > for you, so you can just drop this line. OK > > - 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++; > > You can add multiple pages at once, whether they're compound or not. So > replace this entire loop with: > > bio_add_page(clone, page, remaining_size, 0); This should be min((unsigned)PAGE_SIZE << order, remaining_size), because we may allocate less than remaining_size. > > @@ -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); > > + } > > You can simplify this by using the folio code. > > struct folio_iter fi; > > bio_for_each_folio_all(fi, bio) { > if (folio_test_large(folio)) > folio_put(folio); > else > mempool_free(&folio->page, &cc->page_pool); > } OK. I'm sending version 2 of the patch. > (further work would actually convert this driver to use folios instead > of pages) Mikulas
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); + } } }
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@redhat.com> --- drivers/md/dm-crypt.c | 50 ++++++++++++++++++++++++++++++++++++++++++-------- 1 file changed, 42 insertions(+), 8 deletions(-)