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Message-Id: <1549550196-25581-1-git-send-email-ilias.apalodimas@linaro.org>
Date: Thu, 7 Feb 2019 16:36:36 +0200
From: Ilias Apalodimas <ilias.apalodimas@...aro.org>
To: brouer@...hat.com, tariqt@...lanox.com, toke@...hat.com
Cc: davem@...emloft.net, netdev@...r.kernel.org,
mgorman@...hsingularity.net, linux-mm@...ck.org,
Ilias Apalodimas <ilias.apalodimas@...aro.org>
Subject: [RFC, PATCH] net: page_pool: Don't use page->private to store dma_addr_t
As pointed out in
https://www.mail-archive.com/netdev@vger.kernel.org/msg257926.html
the current page_pool implementation stores dma_addr_t in page->private.
This won't work on 32-bit platforms with 64-bit DMA addresses since the
page->private is an unsigned long and the dma_addr_t a u64.
Since no driver is yet using the DMA mapping capabilities of the API let's
try and fix this by shadowing struct_page and use 'struct list_head lru'
to store and retrieve DMA addresses from network drivers.
As long as the addresses returned from dma_map_page() are aligned the
first bit, used by the compound pages code should not be set.
Signed-off-by: Ilias Apalodimas <ilias.apalodimas@...aro.org>
Signed-off-by: Jesper Dangaard Brouer <brouer@...hat.com>
---
include/net/page_pool.h | 55 +++++++++++++++++++++++++++++++++++++++++++++++++
net/core/page_pool.c | 18 ++++++++++++----
2 files changed, 69 insertions(+), 4 deletions(-)
diff --git a/include/net/page_pool.h b/include/net/page_pool.h
index 694d055..618f2e5 100644
--- a/include/net/page_pool.h
+++ b/include/net/page_pool.h
@@ -98,6 +98,52 @@ struct page_pool {
struct ptr_ring ring;
};
+/* Until we can update struct-page, have a shadow struct-page, that
+ * include our use-case
+ * Used to store retrieve dma addresses from network drivers.
+ * Never access this directly, use helper functions provided
+ * page_pool_get_dma_addr()
+ */
+struct page_shadow {
+ unsigned long flags; /* Atomic flags, some possibly
+ * updated asynchronously
+ */
+ /*
+ * Five words (20/40 bytes) are available in this union.
+ * WARNING: bit 0 of the first word is used for PageTail(). That
+ * means the other users of this union MUST NOT use the bit to
+ * avoid collision and false-positive PageTail().
+ */
+ union {
+ struct { /* Page cache and anonymous pages */
+ /**
+ * @lru: Pageout list, eg. active_list protected by
+ * zone_lru_lock. Sometimes used as a generic list
+ * by the page owner.
+ */
+ struct list_head lru;
+ /* See page-flags.h for PAGE_MAPPING_FLAGS */
+ struct address_space *mapping;
+ pgoff_t index; /* Our offset within mapping. */
+ /**
+ * @private: Mapping-private opaque data.
+ * Usually used for buffer_heads if PagePrivate.
+ * Used for swp_entry_t if PageSwapCache.
+ * Indicates order in the buddy system if PageBuddy.
+ */
+ unsigned long private;
+ };
+ struct { /* page_pool used by netstack */
+ /**
+ * @dma_addr: Page_pool need to store DMA-addr, and
+ * cannot use @private, as DMA-mappings can be 64bit
+ * even on 32-bit Architectures.
+ */
+ dma_addr_t dma_addr; /* Shares area with @lru */
+ };
+ };
+};
+
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)
@@ -141,4 +187,13 @@ static inline bool is_page_pool_compiled_in(void)
#endif
}
+static inline dma_addr_t page_pool_get_dma_addr(struct page *page)
+{
+ struct page_shadow *_page;
+
+ _page = (struct page_shadow *)page;
+
+ return _page->dma_addr;
+}
+
#endif /* _NET_PAGE_POOL_H */
diff --git a/net/core/page_pool.c b/net/core/page_pool.c
index 43a932c..1a956a6 100644
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c
@@ -111,6 +111,7 @@ noinline
static struct page *__page_pool_alloc_pages_slow(struct page_pool *pool,
gfp_t _gfp)
{
+ struct page_shadow *_page;
struct page *page;
gfp_t gfp = _gfp;
dma_addr_t dma;
@@ -136,7 +137,7 @@ static struct page *__page_pool_alloc_pages_slow(struct page_pool *pool,
if (!(pool->p.flags & PP_FLAG_DMA_MAP))
goto skip_dma_map;
- /* Setup DMA mapping: use page->private for DMA-addr
+ /* Setup DMA mapping: use struct-page area for storing DMA-addr
* This mapping is kept for lifetime of page, until leaving pool.
*/
dma = dma_map_page(pool->p.dev, page, 0,
@@ -146,7 +147,8 @@ static struct page *__page_pool_alloc_pages_slow(struct page_pool *pool,
put_page(page);
return NULL;
}
- set_page_private(page, dma); /* page->private = dma; */
+ _page = (struct page_shadow *)page;
+ _page->dma_addr = dma;
skip_dma_map:
/* When page just alloc'ed is should/must have refcnt 1. */
@@ -175,13 +177,21 @@ EXPORT_SYMBOL(page_pool_alloc_pages);
static void __page_pool_clean_page(struct page_pool *pool,
struct page *page)
{
+ struct page_shadow *_page = (struct page_shadow *)page;
+ dma_addr_t dma;
+
if (!(pool->p.flags & PP_FLAG_DMA_MAP))
return;
+ dma = _page->dma_addr;
+
/* DMA unmap */
- dma_unmap_page(pool->p.dev, page_private(page),
+ dma_unmap_page(pool->p.dev, dma,
PAGE_SIZE << pool->p.order, pool->p.dma_dir);
- set_page_private(page, 0);
+ _page->dma_addr = 0;
+ /* 1. Make sure we don't need to list-init page->lru.
+ * 2. What does it mean: bit 0 of LRU first word is used for PageTail()
+ */
}
/* Return a page to the page allocator, cleaning up our state */
--
2.7.4
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