Re: [PATCH 7/7] net: page_pool: use alloc_pages_bulk in refill code path
On Fri, 12 Mar 2021 22:05:45 +0200
Ilias Apalodimas wrote:
> [...]
> > 6. return last_page
> >
> > > + /* Remaining pages store in alloc.cache */
> > > + list_for_each_entry_safe(page, next, _list, lru) {
> > > + list_del(>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?
>
> Oops, I completely missed that. Alexander is right here.
Well, the put_page() case can never happen as the pool->alloc.cache[]
is known to be empty when this function is called. I do agree that the
code looks cumbersome and should free the DMA mapping, if it could
happen.
--
Best regards,
Jesper Dangaard Brouer
MSc.CS, Principal Kernel Engineer at Red Hat
LinkedIn: http://www.linkedin.com/in/brouer
Re: [PATCH 7/7] net: page_pool: use alloc_pages_bulk in refill code path
On Sat, 13 Mar 2021 13:30:58 + Mel Gorman wrote: > On Fri, Mar 12, 2021 at 11:44:09AM -0800, Alexander Duyck wrote: > > > - /* 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, > > > _list))) > > > return NULL; > > > > > > + /* First page is extracted and returned to caller */ > > > + first_page = list_first_entry(_list, struct page, lru); > > > + list_del(_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. > > > > I think you're right but I'm punting this to Jesper to fix. He's more > familiar with this particular code and can verify the performance is > still ok for high speed networks. Yes, I'll take a look at this, and updated the patch accordingly (and re-run the performance tests). -- Best regards, Jesper Dangaard Brouer MSc.CS, Principal Kernel Engineer at Red Hat LinkedIn: http://www.linkedin.com/in/brouer
Re: [PATCH 7/7] net: page_pool: use alloc_pages_bulk in refill code path
On Fri, Mar 12, 2021 at 11:44:09AM -0800, Alexander Duyck wrote: > > - /* 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, > > _list))) > > return NULL; > > > > + /* First page is extracted and returned to caller */ > > + first_page = list_first_entry(_list, struct page, lru); > > + list_del(_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. > I think you're right but I'm punting this to Jesper to fix. He's more familiar with this particular code and can verify the performance is still ok for high speed networks. -- Mel Gorman SUSE Labs
Re: [PATCH 7/7] net: page_pool: use alloc_pages_bulk in refill code path
[...]
> 6. return last_page
>
> > + /* Remaining pages store in alloc.cache */
> > + list_for_each_entry_safe(page, next, _list, lru) {
> > + list_del(>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?
Oops, I completely missed that. Alexander is right here.
>
> > + }
> > + }
> > +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
> >
Cheers
/Ilias
Re: [PATCH 7/7] net: page_pool: use alloc_pages_bulk in refill code path
On Fri, Mar 12, 2021 at 7:43 AM Mel Gorman wrote:
>
> From: Jesper Dangaard Brouer
>
> 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
> Signed-off-by: Mel Gorman
> Reviewed-by: Ilias Apalodimas
> ---
> 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,
> _list)))
> return NULL;
>
> + /* First page is extracted and returned to caller */
> + first_page = list_first_entry(_list, struct page, lru);
> + list_del(_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, _list, lru) {
> + list_del(>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))) {
> +
