Re: [PATCH 7/7] net: page_pool: use alloc_pages_bulk in refill code path

[...]

6. return last_page

quoted

+       /* 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.

quoted

+               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?

Oops, I completely missed that. Alexander is right here.

quoted

+               }
+       }
+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.

quoted

                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

Cheers
/Ilias