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Message-Id: <20231123022516.6757-1-liangchen.linux@gmail.com>
Date: Thu, 23 Nov 2023 10:25:14 +0800
From: Liang Chen <liangchen.linux@...il.com>
To: davem@...emloft.net,
edumazet@...gle.com,
kuba@...nel.org,
pabeni@...hat.com,
hawk@...nel.org,
ilias.apalodimas@...aro.org,
linyunsheng@...wei.com
Cc: netdev@...r.kernel.org,
linux-mm@...ck.org,
liangchen.linux@...il.com
Subject: [PATCH net-next v2 1/3] page_pool: Rename pp_frag_count to pp_ref_count
To support multiple users referencing the same fragment, pp_frag_count is
renamed to pp_ref_count to better reflect its actual meaning based on the
suggestion from [1].
[1]
http://lore.kernel.org/netdev/f71d9448-70c8-8793-dc9a-0eb48a570300@huawei.com
Signed-off-by: Liang Chen <liangchen.linux@...il.com>
---
include/linux/mm_types.h | 2 +-
include/net/page_pool/helpers.h | 31 ++++++++++++++++++-------------
2 files changed, 19 insertions(+), 14 deletions(-)
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 957ce38768b2..64e4572ef06d 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -125,7 +125,7 @@ struct page {
struct page_pool *pp;
unsigned long _pp_mapping_pad;
unsigned long dma_addr;
- atomic_long_t pp_frag_count;
+ atomic_long_t pp_ref_count;
};
struct { /* Tail pages of compound page */
unsigned long compound_head; /* Bit zero is set */
diff --git a/include/net/page_pool/helpers.h b/include/net/page_pool/helpers.h
index 4ebd544ae977..a6dc9412c9ae 100644
--- a/include/net/page_pool/helpers.h
+++ b/include/net/page_pool/helpers.h
@@ -29,7 +29,7 @@
* page allocated from page pool. Page splitting enables memory saving and thus
* avoids TLB/cache miss for data access, but there also is some cost to
* implement page splitting, mainly some cache line dirtying/bouncing for
- * 'struct page' and atomic operation for page->pp_frag_count.
+ * 'struct page' and atomic operation for page->pp_ref_count.
*
* The API keeps track of in-flight pages, in order to let API users know when
* it is safe to free a page_pool object, the API users must call
@@ -214,61 +214,66 @@ inline enum dma_data_direction page_pool_get_dma_dir(struct page_pool *pool)
return pool->p.dma_dir;
}
-/* pp_frag_count represents the number of writers who can update the page
+/* pp_ref_count represents the number of writers who can update the page
* either by updating skb->data or via DMA mappings for the device.
* We can't rely on the page refcnt for that as we don't know who might be
* holding page references and we can't reliably destroy or sync DMA mappings
* of the fragments.
*
- * When pp_frag_count reaches 0 we can either recycle the page if the page
+ * pp_ref_count initially corresponds to the number of fragments. However,
+ * when multiple users start to reference a single fragment, for example in
+ * skb_try_coalesce, the pp_ref_count will become greater than the number of
+ * fragments.
+ *
+ * When pp_ref_count reaches 0 we can either recycle the page if the page
* refcnt is 1 or return it back to the memory allocator and destroy any
* mappings we have.
*/
static inline void page_pool_fragment_page(struct page *page, long nr)
{
- atomic_long_set(&page->pp_frag_count, nr);
+ atomic_long_set(&page->pp_ref_count, nr);
}
static inline long page_pool_defrag_page(struct page *page, long nr)
{
long ret;
- /* If nr == pp_frag_count then we have cleared all remaining
+ /* If nr == pp_ref_count then we have cleared all remaining
* references to the page:
* 1. 'n == 1': no need to actually overwrite it.
* 2. 'n != 1': overwrite it with one, which is the rare case
- * for pp_frag_count draining.
+ * for pp_ref_count draining.
*
* The main advantage to doing this is that not only we avoid a atomic
* update, as an atomic_read is generally a much cheaper operation than
* an atomic update, especially when dealing with a page that may be
- * partitioned into only 2 or 3 pieces; but also unify the pp_frag_count
+ * partitioned into only 2 or 3 pieces; but also unify the pp_ref_count
* handling by ensuring all pages have partitioned into only 1 piece
* initially, and only overwrite it when the page is partitioned into
* more than one piece.
*/
- if (atomic_long_read(&page->pp_frag_count) == nr) {
+ if (atomic_long_read(&page->pp_ref_count) == nr) {
/* As we have ensured nr is always one for constant case using
* the BUILD_BUG_ON(), only need to handle the non-constant case
- * here for pp_frag_count draining, which is a rare case.
+ * here for pp_ref_count draining, which is a rare case.
*/
BUILD_BUG_ON(__builtin_constant_p(nr) && nr != 1);
if (!__builtin_constant_p(nr))
- atomic_long_set(&page->pp_frag_count, 1);
+ atomic_long_set(&page->pp_ref_count, 1);
return 0;
}
- ret = atomic_long_sub_return(nr, &page->pp_frag_count);
+ ret = atomic_long_sub_return(nr, &page->pp_ref_count);
WARN_ON(ret < 0);
- /* We are the last user here too, reset pp_frag_count back to 1 to
+ /* We are the last user here too, reset pp_ref_count back to 1 to
* ensure all pages have been partitioned into 1 piece initially,
* this should be the rare case when the last two fragment users call
* page_pool_defrag_page() currently.
*/
if (unlikely(!ret))
- atomic_long_set(&page->pp_frag_count, 1);
+ atomic_long_set(&page->pp_ref_count, 1);
return ret;
}
--
2.31.1
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