On Fri, Mar 12, 2021 at 7:43 AM Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> wrote: > > From: Jesper Dangaard Brouer <brouer@xxxxxxxxxx> > > There are cases where the page_pool need to refill with pages from the > page allocator. Some workloads cause the page_pool to release pages > instead of recycling these pages. > > For these workload it can improve performance to bulk alloc pages from > the page-allocator to refill the alloc cache. > > For XDP-redirect workload with 100G mlx5 driver (that use page_pool) > redirecting xdp_frame packets into a veth, that does XDP_PASS to create > an SKB from the xdp_frame, which then cannot return the page to the > page_pool. In this case, we saw[1] an improvement of 18.8% from using > the alloc_pages_bulk API (3,677,958 pps -> 4,368,926 pps). > > [1] https://github.com/xdp-project/xdp-project/blob/master/areas/mem/page_pool06_alloc_pages_bulk.org > > Signed-off-by: Jesper Dangaard Brouer <brouer@xxxxxxxxxx> > Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> > Reviewed-by: Ilias Apalodimas <ilias.apalodimas@xxxxxxxxxx> > --- > net/core/page_pool.c | 62 ++++++++++++++++++++++++++++---------------- > 1 file changed, 39 insertions(+), 23 deletions(-) > > diff --git a/net/core/page_pool.c b/net/core/page_pool.c > index 40e1b2beaa6c..a5889f1b86aa 100644 > --- a/net/core/page_pool.c > +++ b/net/core/page_pool.c > @@ -208,44 +208,60 @@ noinline > static struct page *__page_pool_alloc_pages_slow(struct page_pool *pool, > gfp_t _gfp) > { > + const int bulk = PP_ALLOC_CACHE_REFILL; > + struct page *page, *next, *first_page; > unsigned int pp_flags = pool->p.flags; > - struct page *page; > + unsigned int pp_order = pool->p.order; > + int pp_nid = pool->p.nid; > + LIST_HEAD(page_list); > gfp_t gfp = _gfp; > > - /* We could always set __GFP_COMP, and avoid this branch, as > - * prep_new_page() can handle order-0 with __GFP_COMP. > - */ > - if (pool->p.order) > + /* Don't support bulk alloc for high-order pages */ > + if (unlikely(pp_order)) { > gfp |= __GFP_COMP; > + first_page = alloc_pages_node(pp_nid, gfp, pp_order); > + if (unlikely(!first_page)) > + return NULL; > + goto out; > + } > > - /* FUTURE development: > - * > - * Current slow-path essentially falls back to single page > - * allocations, which doesn't improve performance. This code > - * need bulk allocation support from the page allocator code. > - */ > - > - /* Cache was empty, do real allocation */ > -#ifdef CONFIG_NUMA > - page = alloc_pages_node(pool->p.nid, gfp, pool->p.order); > -#else > - page = alloc_pages(gfp, pool->p.order); > -#endif > - if (!page) > + if (unlikely(!__alloc_pages_bulk(gfp, pp_nid, NULL, bulk, &page_list))) > return NULL; > > + /* First page is extracted and returned to caller */ > + first_page = list_first_entry(&page_list, struct page, lru); > + list_del(&first_page->lru); > + This seems kind of broken to me. If you pull the first page and then cannot map it you end up returning NULL even if you placed a number of pages in the cache. It might make more sense to have the loop below record a pointer to the last page you processed and handle things in two stages so that on the first iteration you map one page. So something along the lines of: 1. Initialize last_page to NULL for each page in the list 2. Map page 3. If last_page is non-NULL, move to cache 4. Assign page to last_page 5. Return to step 2 for each page in list 6. return last_page > + /* Remaining pages store in alloc.cache */ > + list_for_each_entry_safe(page, next, &page_list, lru) { > + list_del(&page->lru); > + if ((pp_flags & PP_FLAG_DMA_MAP) && > + unlikely(!page_pool_dma_map(pool, page))) { > + put_page(page); > + continue; > + } So if you added a last_page pointer what you could do is check for it here and assign it to the alloc cache. If last_page is not set the block would be skipped. > + if (likely(pool->alloc.count < PP_ALLOC_CACHE_SIZE)) { > + pool->alloc.cache[pool->alloc.count++] = page; > + pool->pages_state_hold_cnt++; > + trace_page_pool_state_hold(pool, page, > + pool->pages_state_hold_cnt); > + } else { > + put_page(page); If you are just calling put_page here aren't you leaking DMA mappings? Wouldn't you need to potentially unmap the page before you call put_page on it? > + } > + } > +out: > if ((pp_flags & PP_FLAG_DMA_MAP) && > - unlikely(!page_pool_dma_map(pool, page))) { > - put_page(page); > + unlikely(!page_pool_dma_map(pool, first_page))) { > + put_page(first_page); I would probably move this block up and make it a part of the pp_order block above. Also since you are doing this in 2 spots it might make sense to look at possibly making this an inline function. > return NULL; > } > > /* Track how many pages are held 'in-flight' */ > pool->pages_state_hold_cnt++; > - trace_page_pool_state_hold(pool, page, pool->pages_state_hold_cnt); > + trace_page_pool_state_hold(pool, first_page, pool->pages_state_hold_cnt); > > /* When page just alloc'ed is should/must have refcnt 1. */ > - return page; > + return first_page; > } > > /* For using page_pool replace: alloc_pages() API calls, but provide > -- > 2.26.2 >
