Commit ff7d6b27 authored by Jesper Dangaard Brouer's avatar Jesper Dangaard Brouer Committed by David S. Miller

page_pool: refurbish version of page_pool code

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: default avatarJesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 8d5d8852
......@@ -30,6 +30,7 @@ config MLX5_CORE_EN
bool "Mellanox Technologies ConnectX-4 Ethernet support"
depends on NETDEVICES && ETHERNET && INET && PCI && MLX5_CORE
depends on IPV6=y || IPV6=n || MLX5_CORE=m
select PAGE_POOL
default n
---help---
Ethernet support in Mellanox Technologies ConnectX-4 NIC.
......
/* SPDX-License-Identifier: GPL-2.0
*
* page_pool.h
* Author: Jesper Dangaard Brouer <netoptimizer@brouer.com>
* Copyright (C) 2016 Red Hat, Inc.
*/
/**
* DOC: page_pool allocator
*
* This page_pool allocator is optimized for the XDP mode that
* uses one-frame-per-page, but have fallbacks that act like the
* regular page allocator APIs.
*
* Basic use involve replacing alloc_pages() calls with the
* page_pool_alloc_pages() call. Drivers should likely use
* page_pool_dev_alloc_pages() replacing dev_alloc_pages().
*
* If page_pool handles DMA mapping (use page->private), then API user
* is responsible for invoking page_pool_put_page() once. In-case of
* elevated refcnt, the DMA state is released, assuming other users of
* the page will eventually call put_page().
*
* If no DMA mapping is done, then it can act as shim-layer that
* fall-through to alloc_page. As no state is kept on the page, the
* regular put_page() call is sufficient.
*/
#ifndef _NET_PAGE_POOL_H
#define _NET_PAGE_POOL_H
#include <linux/mm.h> /* Needed by ptr_ring */
#include <linux/ptr_ring.h>
#include <linux/dma-direction.h>
#define PP_FLAG_DMA_MAP 1 /* Should page_pool do the DMA map/unmap */
#define PP_FLAG_ALL PP_FLAG_DMA_MAP
/*
* Fast allocation side cache array/stack
*
* The cache size and refill watermark is related to the network
* use-case. The NAPI budget is 64 packets. After a NAPI poll the RX
* ring is usually refilled and the max consumed elements will be 64,
* thus a natural max size of objects needed in the cache.
*
* Keeping room for more objects, is due to XDP_DROP use-case. As
* XDP_DROP allows the opportunity to recycle objects directly into
* this array, as it shares the same softirq/NAPI protection. If
* cache is already full (or partly full) then the XDP_DROP recycles
* would have to take a slower code path.
*/
#define PP_ALLOC_CACHE_SIZE 128
#define PP_ALLOC_CACHE_REFILL 64
struct pp_alloc_cache {
u32 count;
void *cache[PP_ALLOC_CACHE_SIZE];
};
struct page_pool_params {
unsigned int flags;
unsigned int order;
unsigned int pool_size;
int nid; /* Numa node id to allocate from pages from */
struct device *dev; /* device, for DMA pre-mapping purposes */
enum dma_data_direction dma_dir; /* DMA mapping direction */
};
struct page_pool {
struct rcu_head rcu;
struct page_pool_params p;
/*
* Data structure for allocation side
*
* Drivers allocation side usually already perform some kind
* of resource protection. Piggyback on this protection, and
* require driver to protect allocation side.
*
* For NIC drivers this means, allocate a page_pool per
* RX-queue. As the RX-queue is already protected by
* Softirq/BH scheduling and napi_schedule. NAPI schedule
* guarantee that a single napi_struct will only be scheduled
* on a single CPU (see napi_schedule).
*/
struct pp_alloc_cache alloc ____cacheline_aligned_in_smp;
/* Data structure for storing recycled pages.
*
* Returning/freeing pages is more complicated synchronization
* wise, because free's can happen on remote CPUs, with no
* association with allocation resource.
*
* Use ptr_ring, as it separates consumer and producer
* effeciently, it a way that doesn't bounce cache-lines.
*
* TODO: Implement bulk return pages into this structure.
*/
struct ptr_ring ring;
};
struct page *page_pool_alloc_pages(struct page_pool *pool, gfp_t gfp);
static inline struct page *page_pool_dev_alloc_pages(struct page_pool *pool)
{
gfp_t gfp = (GFP_ATOMIC | __GFP_NOWARN);
return page_pool_alloc_pages(pool, gfp);
}
struct page_pool *page_pool_create(const struct page_pool_params *params);
void page_pool_destroy(struct page_pool *pool);
/* Never call this directly, use helpers below */
void __page_pool_put_page(struct page_pool *pool,
struct page *page, bool allow_direct);
static inline void page_pool_put_page(struct page_pool *pool, struct page *page)
{
__page_pool_put_page(pool, page, false);
}
/* Very limited use-cases allow recycle direct */
static inline void page_pool_recycle_direct(struct page_pool *pool,
struct page *page)
{
__page_pool_put_page(pool, page, true);
}
#endif /* _NET_PAGE_POOL_H */
......@@ -423,6 +423,9 @@ config MAY_USE_DEVLINK
on MAY_USE_DEVLINK to ensure they do not cause link errors when
devlink is a loadable module and the driver using it is built-in.
config PAGE_POOL
bool
endif # if NET
# Used by archs to tell that they support BPF JIT compiler plus which flavour.
......
......@@ -14,6 +14,7 @@ obj-y += dev.o ethtool.o dev_addr_lists.o dst.o netevent.o \
fib_notifier.o xdp.o
obj-y += net-sysfs.o
obj-$(CONFIG_PAGE_POOL) += page_pool.o
obj-$(CONFIG_PROC_FS) += net-procfs.o
obj-$(CONFIG_NET_PKTGEN) += pktgen.o
obj-$(CONFIG_NETPOLL) += netpoll.o
......
/* SPDX-License-Identifier: GPL-2.0
*
* page_pool.c
* Author: Jesper Dangaard Brouer <netoptimizer@brouer.com>
* Copyright (C) 2016 Red Hat, Inc.
*/
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/slab.h>
#include <net/page_pool.h>
#include <linux/dma-direction.h>
#include <linux/dma-mapping.h>
#include <linux/page-flags.h>
#include <linux/mm.h> /* for __put_page() */
static int page_pool_init(struct page_pool *pool,
const struct page_pool_params *params)
{
unsigned int ring_qsize = 1024; /* Default */
memcpy(&pool->p, params, sizeof(pool->p));
/* Validate only known flags were used */
if (pool->p.flags & ~(PP_FLAG_ALL))
return -EINVAL;
if (pool->p.pool_size)
ring_qsize = pool->p.pool_size;
/* Sanity limit mem that can be pinned down */
if (ring_qsize > 32768)
return -E2BIG;
/* DMA direction is either DMA_FROM_DEVICE or DMA_BIDIRECTIONAL.
* DMA_BIDIRECTIONAL is for allowing page used for DMA sending,
* which is the XDP_TX use-case.
*/
if ((pool->p.dma_dir != DMA_FROM_DEVICE) &&
(pool->p.dma_dir != DMA_BIDIRECTIONAL))
return -EINVAL;
if (ptr_ring_init(&pool->ring, ring_qsize, GFP_KERNEL) < 0)
return -ENOMEM;
return 0;
}
struct page_pool *page_pool_create(const struct page_pool_params *params)
{
struct page_pool *pool;
int err = 0;
pool = kzalloc_node(sizeof(*pool), GFP_KERNEL, params->nid);
if (!pool)
return ERR_PTR(-ENOMEM);
err = page_pool_init(pool, params);
if (err < 0) {
pr_warn("%s() gave up with errno %d\n", __func__, err);
kfree(pool);
return ERR_PTR(err);
}
return pool;
}
EXPORT_SYMBOL(page_pool_create);
/* fast path */
static struct page *__page_pool_get_cached(struct page_pool *pool)
{
struct ptr_ring *r = &pool->ring;
struct page *page;
/* Quicker fallback, avoid locks when ring is empty */
if (__ptr_ring_empty(r))
return NULL;
/* Test for safe-context, caller should provide this guarantee */
if (likely(in_serving_softirq())) {
if (likely(pool->alloc.count)) {
/* Fast-path */
page = pool->alloc.cache[--pool->alloc.count];
return page;
}
/* Slower-path: Alloc array empty, time to refill
*
* Open-coded bulk ptr_ring consumer.
*
* Discussion: the ring consumer lock is not really
* needed due to the softirq/NAPI protection, but
* later need the ability to reclaim pages on the
* ring. Thus, keeping the locks.
*/
spin_lock(&r->consumer_lock);
while ((page = __ptr_ring_consume(r))) {
if (pool->alloc.count == PP_ALLOC_CACHE_REFILL)
break;
pool->alloc.cache[pool->alloc.count++] = page;
}
spin_unlock(&r->consumer_lock);
return page;
}
/* Slow-path: Get page from locked ring queue */
page = ptr_ring_consume(&pool->ring);
return page;
}
/* slow path */
noinline
static struct page *__page_pool_alloc_pages_slow(struct page_pool *pool,
gfp_t _gfp)
{
struct page *page;
gfp_t gfp = _gfp;
dma_addr_t dma;
/* 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)
gfp |= __GFP_COMP;
/* 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 */
page = alloc_pages_node(pool->p.nid, gfp, pool->p.order);
if (!page)
return NULL;
if (!(pool->p.flags & PP_FLAG_DMA_MAP))
goto skip_dma_map;
/* Setup DMA mapping: use page->private for DMA-addr
* This mapping is kept for lifetime of page, until leaving pool.
*/
dma = dma_map_page(pool->p.dev, page, 0,
(PAGE_SIZE << pool->p.order),
pool->p.dma_dir);
if (dma_mapping_error(pool->p.dev, dma)) {
put_page(page);
return NULL;
}
set_page_private(page, dma); /* page->private = dma; */
skip_dma_map:
/* When page just alloc'ed is should/must have refcnt 1. */
return page;
}
/* For using page_pool replace: alloc_pages() API calls, but provide
* synchronization guarantee for allocation side.
*/
struct page *page_pool_alloc_pages(struct page_pool *pool, gfp_t gfp)
{
struct page *page;
/* Fast-path: Get a page from cache */
page = __page_pool_get_cached(pool);
if (page)
return page;
/* Slow-path: cache empty, do real allocation */
page = __page_pool_alloc_pages_slow(pool, gfp);
return page;
}
EXPORT_SYMBOL(page_pool_alloc_pages);
/* Cleanup page_pool state from page */
static void __page_pool_clean_page(struct page_pool *pool,
struct page *page)
{
if (!(pool->p.flags & PP_FLAG_DMA_MAP))
return;
/* DMA unmap */
dma_unmap_page(pool->p.dev, page_private(page),
PAGE_SIZE << pool->p.order, pool->p.dma_dir);
set_page_private(page, 0);
}
/* Return a page to the page allocator, cleaning up our state */
static void __page_pool_return_page(struct page_pool *pool, struct page *page)
{
__page_pool_clean_page(pool, page);
put_page(page);
/* An optimization would be to call __free_pages(page, pool->p.order)
* knowing page is not part of page-cache (thus avoiding a
* __page_cache_release() call).
*/
}
static bool __page_pool_recycle_into_ring(struct page_pool *pool,
struct page *page)
{
int ret;
/* BH protection not needed if current is serving softirq */
if (in_serving_softirq())
ret = ptr_ring_produce(&pool->ring, page);
else
ret = ptr_ring_produce_bh(&pool->ring, page);
return (ret == 0) ? true : false;
}
/* Only allow direct recycling in special circumstances, into the
* alloc side cache. E.g. during RX-NAPI processing for XDP_DROP use-case.
*
* Caller must provide appropriate safe context.
*/
static bool __page_pool_recycle_direct(struct page *page,
struct page_pool *pool)
{
if (unlikely(pool->alloc.count == PP_ALLOC_CACHE_SIZE))
return false;
/* Caller MUST have verified/know (page_ref_count(page) == 1) */
pool->alloc.cache[pool->alloc.count++] = page;
return true;
}
void __page_pool_put_page(struct page_pool *pool,
struct page *page, bool allow_direct)
{
/* This allocator is optimized for the XDP mode that uses
* one-frame-per-page, but have fallbacks that act like the
* regular page allocator APIs.
*
* refcnt == 1 means page_pool owns page, and can recycle it.
*/
if (likely(page_ref_count(page) == 1)) {
/* Read barrier done in page_ref_count / READ_ONCE */
if (allow_direct && in_serving_softirq())
if (__page_pool_recycle_direct(page, pool))
return;
if (!__page_pool_recycle_into_ring(pool, page)) {
/* Cache full, fallback to free pages */
__page_pool_return_page(pool, page);
}
return;
}
/* Fallback/non-XDP mode: API user have elevated refcnt.
*
* Many drivers split up the page into fragments, and some
* want to keep doing this to save memory and do refcnt based
* recycling. Support this use case too, to ease drivers
* switching between XDP/non-XDP.
*
* In-case page_pool maintains the DMA mapping, API user must
* call page_pool_put_page once. In this elevated refcnt
* case, the DMA is unmapped/released, as driver is likely
* doing refcnt based recycle tricks, meaning another process
* will be invoking put_page.
*/
__page_pool_clean_page(pool, page);
put_page(page);
}
EXPORT_SYMBOL(__page_pool_put_page);
static void __page_pool_empty_ring(struct page_pool *pool)
{
struct page *page;
/* Empty recycle ring */
while ((page = ptr_ring_consume(&pool->ring))) {
/* Verify the refcnt invariant of cached pages */
if (!(page_ref_count(page) == 1))
pr_crit("%s() page_pool refcnt %d violation\n",
__func__, page_ref_count(page));
__page_pool_return_page(pool, page);
}
}
static void __page_pool_destroy_rcu(struct rcu_head *rcu)
{
struct page_pool *pool;
pool = container_of(rcu, struct page_pool, rcu);
WARN(pool->alloc.count, "API usage violation");
__page_pool_empty_ring(pool);
ptr_ring_cleanup(&pool->ring, NULL);
kfree(pool);
}
/* Cleanup and release resources */
void page_pool_destroy(struct page_pool *pool)
{
struct page *page;
/* Empty alloc cache, assume caller made sure this is
* no-longer in use, and page_pool_alloc_pages() cannot be
* call concurrently.
*/
while (pool->alloc.count) {
page = pool->alloc.cache[--pool->alloc.count];
__page_pool_return_page(pool, page);
}
/* No more consumers should exist, but producers could still
* be in-flight.
*/
__page_pool_empty_ring(pool);
/* An xdp_mem_allocator can still ref page_pool pointer */
call_rcu(&pool->rcu, __page_pool_destroy_rcu);
}
EXPORT_SYMBOL(page_pool_destroy);
Markdown is supported
0%
or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment