Re: [PATCH 7/7] net: page_pool: use alloc_pages_bulk in refill code path
From: Alexander Duyck <hidden>
Date: 2021-03-12 19:44:57
Also in:
linux-mm, linux-nfs, lkml
On Fri, Mar 12, 2021 at 7:43 AM Mel Gorman [off-list ref] wrote:
quoted hunk ↗ jump to hunk
From: Jesper Dangaard Brouer <redacted> 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 <redacted> Signed-off-by: Mel Gorman <redacted> Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org> --- 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