![Jesper Dangaard Brouer](/assets/img/avatar_default.png)
Need a fast page recycle mechanism for ndo_xdp_xmit API for returning pages on DMA-TX completion time, which have good cross CPU performance, given DMA-TX completion time can happen on a remote CPU. Refurbish my page_pool code, that was presented[1] at MM-summit 2016. Adapted page_pool code to not depend the page allocator and integration into struct page. The DMA mapping feature is kept, even-though it will not be activated/used in this patchset. [1] http://people.netfilter.org/hawk/presentations/MM-summit2016/generic_page_pool_mm_summit2016.pdf V2: Adjustments requested by Tariq - Changed page_pool_create return codes, don't return NULL, only ERR_PTR, as this simplifies err handling in drivers. V4: many small improvements and cleanups - Add DOC comment section, that can be used by kernel-doc - Improve fallback mode, to work better with refcnt based recycling e.g. remove a WARN as pointed out by Tariq e.g. quicker fallback if ptr_ring is empty. V5: Fixed SPDX license as pointed out by Alexei V6: Adjustments requested by Eric Dumazet - Adjust ____cacheline_aligned_in_smp usage/placement - Move rcu_head in struct page_pool - Free pages quicker on destroy, minimize resources delayed an RCU period - Remove code for forward/backward compat ABI interface V8: Issues found by kbuild test robot - Address sparse should be static warnings - Only compile+link when a driver use/select page_pool, mlx5 selects CONFIG_PAGE_POOL, although its first used in two patches Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com> Signed-off-by: David S. Miller <davem@davemloft.net>
318 lines
8.4 KiB
C
318 lines
8.4 KiB
C
/* SPDX-License-Identifier: GPL-2.0
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*
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* page_pool.c
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* Author: Jesper Dangaard Brouer <netoptimizer@brouer.com>
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* Copyright (C) 2016 Red Hat, Inc.
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*/
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#include <linux/types.h>
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#include <linux/kernel.h>
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#include <linux/slab.h>
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#include <net/page_pool.h>
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#include <linux/dma-direction.h>
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#include <linux/dma-mapping.h>
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#include <linux/page-flags.h>
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#include <linux/mm.h> /* for __put_page() */
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static int page_pool_init(struct page_pool *pool,
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const struct page_pool_params *params)
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{
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unsigned int ring_qsize = 1024; /* Default */
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memcpy(&pool->p, params, sizeof(pool->p));
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/* Validate only known flags were used */
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if (pool->p.flags & ~(PP_FLAG_ALL))
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return -EINVAL;
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if (pool->p.pool_size)
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ring_qsize = pool->p.pool_size;
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/* Sanity limit mem that can be pinned down */
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if (ring_qsize > 32768)
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return -E2BIG;
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/* DMA direction is either DMA_FROM_DEVICE or DMA_BIDIRECTIONAL.
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* DMA_BIDIRECTIONAL is for allowing page used for DMA sending,
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* which is the XDP_TX use-case.
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*/
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if ((pool->p.dma_dir != DMA_FROM_DEVICE) &&
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(pool->p.dma_dir != DMA_BIDIRECTIONAL))
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return -EINVAL;
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if (ptr_ring_init(&pool->ring, ring_qsize, GFP_KERNEL) < 0)
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return -ENOMEM;
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return 0;
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}
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struct page_pool *page_pool_create(const struct page_pool_params *params)
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{
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struct page_pool *pool;
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int err = 0;
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pool = kzalloc_node(sizeof(*pool), GFP_KERNEL, params->nid);
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if (!pool)
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return ERR_PTR(-ENOMEM);
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err = page_pool_init(pool, params);
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if (err < 0) {
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pr_warn("%s() gave up with errno %d\n", __func__, err);
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kfree(pool);
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return ERR_PTR(err);
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}
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return pool;
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}
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EXPORT_SYMBOL(page_pool_create);
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/* fast path */
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static struct page *__page_pool_get_cached(struct page_pool *pool)
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{
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struct ptr_ring *r = &pool->ring;
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struct page *page;
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/* Quicker fallback, avoid locks when ring is empty */
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if (__ptr_ring_empty(r))
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return NULL;
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/* Test for safe-context, caller should provide this guarantee */
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if (likely(in_serving_softirq())) {
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if (likely(pool->alloc.count)) {
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/* Fast-path */
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page = pool->alloc.cache[--pool->alloc.count];
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return page;
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}
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/* Slower-path: Alloc array empty, time to refill
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*
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* Open-coded bulk ptr_ring consumer.
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*
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* Discussion: the ring consumer lock is not really
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* needed due to the softirq/NAPI protection, but
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* later need the ability to reclaim pages on the
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* ring. Thus, keeping the locks.
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*/
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spin_lock(&r->consumer_lock);
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while ((page = __ptr_ring_consume(r))) {
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if (pool->alloc.count == PP_ALLOC_CACHE_REFILL)
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break;
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pool->alloc.cache[pool->alloc.count++] = page;
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}
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spin_unlock(&r->consumer_lock);
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return page;
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}
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/* Slow-path: Get page from locked ring queue */
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page = ptr_ring_consume(&pool->ring);
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return page;
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}
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/* slow path */
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noinline
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static struct page *__page_pool_alloc_pages_slow(struct page_pool *pool,
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gfp_t _gfp)
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{
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struct page *page;
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gfp_t gfp = _gfp;
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dma_addr_t dma;
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/* We could always set __GFP_COMP, and avoid this branch, as
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* prep_new_page() can handle order-0 with __GFP_COMP.
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*/
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if (pool->p.order)
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gfp |= __GFP_COMP;
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/* FUTURE development:
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*
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* Current slow-path essentially falls back to single page
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* allocations, which doesn't improve performance. This code
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* need bulk allocation support from the page allocator code.
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*/
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/* Cache was empty, do real allocation */
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page = alloc_pages_node(pool->p.nid, gfp, pool->p.order);
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if (!page)
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return NULL;
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if (!(pool->p.flags & PP_FLAG_DMA_MAP))
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goto skip_dma_map;
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/* Setup DMA mapping: use page->private for DMA-addr
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* This mapping is kept for lifetime of page, until leaving pool.
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*/
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dma = dma_map_page(pool->p.dev, page, 0,
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(PAGE_SIZE << pool->p.order),
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pool->p.dma_dir);
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if (dma_mapping_error(pool->p.dev, dma)) {
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put_page(page);
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return NULL;
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}
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set_page_private(page, dma); /* page->private = dma; */
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skip_dma_map:
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/* When page just alloc'ed is should/must have refcnt 1. */
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return page;
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}
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/* For using page_pool replace: alloc_pages() API calls, but provide
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* synchronization guarantee for allocation side.
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*/
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struct page *page_pool_alloc_pages(struct page_pool *pool, gfp_t gfp)
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{
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struct page *page;
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/* Fast-path: Get a page from cache */
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page = __page_pool_get_cached(pool);
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if (page)
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return page;
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/* Slow-path: cache empty, do real allocation */
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page = __page_pool_alloc_pages_slow(pool, gfp);
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return page;
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}
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EXPORT_SYMBOL(page_pool_alloc_pages);
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/* Cleanup page_pool state from page */
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static void __page_pool_clean_page(struct page_pool *pool,
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struct page *page)
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{
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if (!(pool->p.flags & PP_FLAG_DMA_MAP))
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return;
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/* DMA unmap */
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dma_unmap_page(pool->p.dev, page_private(page),
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PAGE_SIZE << pool->p.order, pool->p.dma_dir);
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set_page_private(page, 0);
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}
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/* Return a page to the page allocator, cleaning up our state */
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static void __page_pool_return_page(struct page_pool *pool, struct page *page)
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{
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__page_pool_clean_page(pool, page);
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put_page(page);
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/* An optimization would be to call __free_pages(page, pool->p.order)
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* knowing page is not part of page-cache (thus avoiding a
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* __page_cache_release() call).
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*/
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}
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static bool __page_pool_recycle_into_ring(struct page_pool *pool,
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struct page *page)
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{
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int ret;
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/* BH protection not needed if current is serving softirq */
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if (in_serving_softirq())
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ret = ptr_ring_produce(&pool->ring, page);
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else
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ret = ptr_ring_produce_bh(&pool->ring, page);
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return (ret == 0) ? true : false;
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}
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/* Only allow direct recycling in special circumstances, into the
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* alloc side cache. E.g. during RX-NAPI processing for XDP_DROP use-case.
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*
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* Caller must provide appropriate safe context.
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*/
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static bool __page_pool_recycle_direct(struct page *page,
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struct page_pool *pool)
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{
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if (unlikely(pool->alloc.count == PP_ALLOC_CACHE_SIZE))
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return false;
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/* Caller MUST have verified/know (page_ref_count(page) == 1) */
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pool->alloc.cache[pool->alloc.count++] = page;
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return true;
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}
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void __page_pool_put_page(struct page_pool *pool,
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struct page *page, bool allow_direct)
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{
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/* This allocator is optimized for the XDP mode that uses
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* one-frame-per-page, but have fallbacks that act like the
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* regular page allocator APIs.
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*
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* refcnt == 1 means page_pool owns page, and can recycle it.
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*/
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if (likely(page_ref_count(page) == 1)) {
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/* Read barrier done in page_ref_count / READ_ONCE */
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if (allow_direct && in_serving_softirq())
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if (__page_pool_recycle_direct(page, pool))
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return;
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if (!__page_pool_recycle_into_ring(pool, page)) {
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/* Cache full, fallback to free pages */
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__page_pool_return_page(pool, page);
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}
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return;
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}
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/* Fallback/non-XDP mode: API user have elevated refcnt.
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*
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* Many drivers split up the page into fragments, and some
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* want to keep doing this to save memory and do refcnt based
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* recycling. Support this use case too, to ease drivers
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* switching between XDP/non-XDP.
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*
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* In-case page_pool maintains the DMA mapping, API user must
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* call page_pool_put_page once. In this elevated refcnt
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* case, the DMA is unmapped/released, as driver is likely
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* doing refcnt based recycle tricks, meaning another process
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* will be invoking put_page.
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*/
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__page_pool_clean_page(pool, page);
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put_page(page);
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}
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EXPORT_SYMBOL(__page_pool_put_page);
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static void __page_pool_empty_ring(struct page_pool *pool)
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{
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struct page *page;
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/* Empty recycle ring */
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while ((page = ptr_ring_consume(&pool->ring))) {
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/* Verify the refcnt invariant of cached pages */
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if (!(page_ref_count(page) == 1))
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pr_crit("%s() page_pool refcnt %d violation\n",
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__func__, page_ref_count(page));
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__page_pool_return_page(pool, page);
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}
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}
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static void __page_pool_destroy_rcu(struct rcu_head *rcu)
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{
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struct page_pool *pool;
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pool = container_of(rcu, struct page_pool, rcu);
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WARN(pool->alloc.count, "API usage violation");
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__page_pool_empty_ring(pool);
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ptr_ring_cleanup(&pool->ring, NULL);
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kfree(pool);
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}
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/* Cleanup and release resources */
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void page_pool_destroy(struct page_pool *pool)
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{
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struct page *page;
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/* Empty alloc cache, assume caller made sure this is
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* no-longer in use, and page_pool_alloc_pages() cannot be
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* call concurrently.
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*/
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while (pool->alloc.count) {
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page = pool->alloc.cache[--pool->alloc.count];
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__page_pool_return_page(pool, page);
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}
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/* No more consumers should exist, but producers could still
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* be in-flight.
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*/
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__page_pool_empty_ring(pool);
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/* An xdp_mem_allocator can still ref page_pool pointer */
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call_rcu(&pool->rcu, __page_pool_destroy_rcu);
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}
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EXPORT_SYMBOL(page_pool_destroy);
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