--- /dev/null
+From: Yunsheng Lin <linyunsheng@huawei.com>
+Date: Fri, 13 Oct 2023 14:48:21 +0800
+Subject: [PATCH] page_pool: fragment API support for 32-bit arch with 64-bit
+ DMA
+
+Currently page_pool_alloc_frag() is not supported in 32-bit
+arch with 64-bit DMA because of the overlap issue between
+pp_frag_count and dma_addr_upper in 'struct page' for those
+arches, which seems to be quite common, see [1], which means
+driver may need to handle it when using fragment API.
+
+It is assumed that the combination of the above arch with an
+address space >16TB does not exist, as all those arches have
+64b equivalent, it seems logical to use the 64b version for a
+system with a large address space. It is also assumed that dma
+address is page aligned when we are dma mapping a page aligned
+buffer, see [2].
+
+That means we're storing 12 bits of 0 at the lower end for a
+dma address, we can reuse those bits for the above arches to
+support 32b+12b, which is 16TB of memory.
+
+If we make a wrong assumption, a warning is emitted so that
+user can report to us.
+
+1. https://lore.kernel.org/all/20211117075652.58299-1-linyunsheng@huawei.com/
+2. https://lore.kernel.org/all/20230818145145.4b357c89@kernel.org/
+
+Tested-by: Alexander Lobakin <aleksander.lobakin@intel.com>
+Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
+CC: Lorenzo Bianconi <lorenzo@kernel.org>
+CC: Alexander Duyck <alexander.duyck@gmail.com>
+CC: Liang Chen <liangchen.linux@gmail.com>
+CC: Guillaume Tucker <guillaume.tucker@collabora.com>
+CC: Matthew Wilcox <willy@infradead.org>
+CC: Linux-MM <linux-mm@kvack.org>
+Link: https://lore.kernel.org/r/20231013064827.61135-2-linyunsheng@huawei.com
+Signed-off-by: Jakub Kicinski <kuba@kernel.org>
+---
+
+--- a/include/linux/mm_types.h
++++ b/include/linux/mm_types.h
+@@ -125,18 +125,7 @@ struct page {
+ struct page_pool *pp;
+ unsigned long _pp_mapping_pad;
+ unsigned long dma_addr;
+- union {
+- /**
+- * dma_addr_upper: might require a 64-bit
+- * value on 32-bit architectures.
+- */
+- unsigned long dma_addr_upper;
+- /**
+- * For frag page support, not supported in
+- * 32-bit architectures with 64-bit DMA.
+- */
+- atomic_long_t pp_frag_count;
+- };
++ atomic_long_t pp_frag_count;
+ };
+ struct { /* Tail pages of compound page */
+ unsigned long compound_head; /* Bit zero is set */
+--- a/include/net/page_pool/helpers.h
++++ b/include/net/page_pool/helpers.h
+@@ -197,7 +197,7 @@ static inline void page_pool_recycle_dir
+ page_pool_put_full_page(pool, page, true);
+ }
+
+-#define PAGE_POOL_DMA_USE_PP_FRAG_COUNT \
++#define PAGE_POOL_32BIT_ARCH_WITH_64BIT_DMA \
+ (sizeof(dma_addr_t) > sizeof(unsigned long))
+
+ /**
+@@ -211,17 +211,25 @@ static inline dma_addr_t page_pool_get_d
+ {
+ dma_addr_t ret = page->dma_addr;
+
+- if (PAGE_POOL_DMA_USE_PP_FRAG_COUNT)
+- ret |= (dma_addr_t)page->dma_addr_upper << 16 << 16;
++ if (PAGE_POOL_32BIT_ARCH_WITH_64BIT_DMA)
++ ret <<= PAGE_SHIFT;
+
+ return ret;
+ }
+
+-static inline void page_pool_set_dma_addr(struct page *page, dma_addr_t addr)
++static inline bool page_pool_set_dma_addr(struct page *page, dma_addr_t addr)
+ {
++ if (PAGE_POOL_32BIT_ARCH_WITH_64BIT_DMA) {
++ page->dma_addr = addr >> PAGE_SHIFT;
++
++ /* We assume page alignment to shave off bottom bits,
++ * if this "compression" doesn't work we need to drop.
++ */
++ return addr != (dma_addr_t)page->dma_addr << PAGE_SHIFT;
++ }
++
+ page->dma_addr = addr;
+- if (PAGE_POOL_DMA_USE_PP_FRAG_COUNT)
+- page->dma_addr_upper = upper_32_bits(addr);
++ return false;
+ }
+
+ static inline bool page_pool_put(struct page_pool *pool)
+--- a/net/core/page_pool.c
++++ b/net/core/page_pool.c
+@@ -211,10 +211,6 @@ static int page_pool_init(struct page_po
+ */
+ }
+
+- if (PAGE_POOL_DMA_USE_PP_FRAG_COUNT &&
+- pool->p.flags & PP_FLAG_PAGE_FRAG)
+- return -EINVAL;
+-
+ #ifdef CONFIG_PAGE_POOL_STATS
+ pool->recycle_stats = alloc_percpu(struct page_pool_recycle_stats);
+ if (!pool->recycle_stats)
+@@ -363,12 +359,20 @@ static bool page_pool_dma_map(struct pag
+ if (dma_mapping_error(pool->p.dev, dma))
+ return false;
+
+- page_pool_set_dma_addr(page, dma);
++ if (page_pool_set_dma_addr(page, dma))
++ goto unmap_failed;
+
+ if (pool->p.flags & PP_FLAG_DMA_SYNC_DEV)
+ page_pool_dma_sync_for_device(pool, page, pool->p.max_len);
+
+ return true;
++
++unmap_failed:
++ WARN_ON_ONCE("unexpected DMA address, please report to netdev@");
++ dma_unmap_page_attrs(pool->p.dev, dma,
++ PAGE_SIZE << pool->p.order, pool->p.dma_dir,
++ DMA_ATTR_SKIP_CPU_SYNC | DMA_ATTR_WEAK_ORDERING);
++ return false;
+ }
+
+ static void page_pool_set_pp_info(struct page_pool *pool,
--- /dev/null
+From: Yunsheng Lin <linyunsheng@huawei.com>
+Date: Fri, 20 Oct 2023 17:59:48 +0800
+Subject: [PATCH] page_pool: unify frag_count handling in
+ page_pool_is_last_frag()
+
+Currently when page_pool_create() is called with
+PP_FLAG_PAGE_FRAG flag, page_pool_alloc_pages() is only
+allowed to be called under the below constraints:
+1. page_pool_fragment_page() need to be called to setup
+ page->pp_frag_count immediately.
+2. page_pool_defrag_page() often need to be called to drain
+ the page->pp_frag_count when there is no more user will
+ be holding on to that page.
+
+Those constraints exist in order to support a page to be
+split into multi fragments.
+
+And those constraints have some overhead because of the
+cache line dirtying/bouncing and atomic update.
+
+Those constraints are unavoidable for case when we need a
+page to be split into more than one fragment, but there is
+also case that we want to avoid the above constraints and
+their overhead when a page can't be split as it can only
+hold a fragment as requested by user, depending on different
+use cases:
+use case 1: allocate page without page splitting.
+use case 2: allocate page with page splitting.
+use case 3: allocate page with or without page splitting
+ depending on the fragment size.
+
+Currently page pool only provide page_pool_alloc_pages() and
+page_pool_alloc_frag() API to enable the 1 & 2 separately,
+so we can not use a combination of 1 & 2 to enable 3, it is
+not possible yet because of the per page_pool flag
+PP_FLAG_PAGE_FRAG.
+
+So in order to allow allocating unsplit page without the
+overhead of split page while still allow allocating split
+page we need to remove the per page_pool flag in
+page_pool_is_last_frag(), as best as I can think of, it seems
+there are two methods as below:
+1. Add per page flag/bit to indicate a page is split or
+ not, which means we might need to update that flag/bit
+ everytime the page is recycled, dirtying the cache line
+ of 'struct page' for use case 1.
+2. Unify the page->pp_frag_count handling for both split and
+ unsplit page by assuming all pages in the page pool is split
+ into a big fragment initially.
+
+As page pool already supports use case 1 without dirtying the
+cache line of 'struct page' whenever a page is recyclable, we
+need to support the above use case 3 with minimal overhead,
+especially not adding any noticeable overhead for use case 1,
+and we are already doing an optimization by not updating
+pp_frag_count in page_pool_defrag_page() for the last fragment
+user, this patch chooses to unify the pp_frag_count handling
+to support the above use case 3.
+
+There is no noticeable performance degradation and some
+justification for unifying the frag_count handling with this
+patch applied using a micro-benchmark testing in [1].
+
+1. https://lore.kernel.org/all/bf2591f8-7b3c-4480-bb2c-31dc9da1d6ac@huawei.com/
+
+Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
+CC: Lorenzo Bianconi <lorenzo@kernel.org>
+CC: Alexander Duyck <alexander.duyck@gmail.com>
+CC: Liang Chen <liangchen.linux@gmail.com>
+CC: Alexander Lobakin <aleksander.lobakin@intel.com>
+Link: https://lore.kernel.org/r/20231020095952.11055-2-linyunsheng@huawei.com
+Signed-off-by: Jakub Kicinski <kuba@kernel.org>
+---
+
+--- a/include/net/page_pool/helpers.h
++++ b/include/net/page_pool/helpers.h
+@@ -115,28 +115,49 @@ static inline long page_pool_defrag_page
+ long ret;
+
+ /* If nr == pp_frag_count then we have cleared all remaining
+- * references to the page. No need to actually overwrite it, instead
+- * we can leave this to be overwritten by the calling function.
++ * 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.
+ *
+- * The main advantage to doing this is that 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.
++ * 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
++ * 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_frag_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.
++ */
++ BUILD_BUG_ON(__builtin_constant_p(nr) && nr != 1);
++ if (!__builtin_constant_p(nr))
++ atomic_long_set(&page->pp_frag_count, 1);
++
+ return 0;
++ }
+
+ ret = atomic_long_sub_return(nr, &page->pp_frag_count);
+ WARN_ON(ret < 0);
++
++ /* We are the last user here too, reset pp_frag_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);
++
+ return ret;
+ }
+
+-static inline bool page_pool_is_last_frag(struct page_pool *pool,
+- struct page *page)
++static inline bool page_pool_is_last_frag(struct page *page)
+ {
+- /* If fragments aren't enabled or count is 0 we were the last user */
+- return !(pool->p.flags & PP_FLAG_PAGE_FRAG) ||
+- (page_pool_defrag_page(page, 1) == 0);
++ /* If page_pool_defrag_page() returns 0, we were the last user */
++ return page_pool_defrag_page(page, 1) == 0;
+ }
+
+ /**
+@@ -161,7 +182,7 @@ static inline void page_pool_put_page(st
+ * allow registering MEM_TYPE_PAGE_POOL, but shield linker.
+ */
+ #ifdef CONFIG_PAGE_POOL
+- if (!page_pool_is_last_frag(pool, page))
++ if (!page_pool_is_last_frag(page))
+ return;
+
+ page_pool_put_defragged_page(pool, page, dma_sync_size, allow_direct);
+--- a/net/core/page_pool.c
++++ b/net/core/page_pool.c
+@@ -380,6 +380,14 @@ static void page_pool_set_pp_info(struct
+ {
+ page->pp = pool;
+ page->pp_magic |= PP_SIGNATURE;
++
++ /* Ensuring all pages have been split into one fragment initially:
++ * page_pool_set_pp_info() is only called once for every page when it
++ * is allocated from the page allocator and page_pool_fragment_page()
++ * is dirtying the same cache line as the page->pp_magic above, so
++ * the overhead is negligible.
++ */
++ page_pool_fragment_page(page, 1);
+ if (pool->p.init_callback)
+ pool->p.init_callback(page, pool->p.init_arg);
+ }
+@@ -676,7 +684,7 @@ void page_pool_put_page_bulk(struct page
+ struct page *page = virt_to_head_page(data[i]);
+
+ /* It is not the last user for the page frag case */
+- if (!page_pool_is_last_frag(pool, page))
++ if (!page_pool_is_last_frag(page))
+ continue;
+
+ page = __page_pool_put_page(pool, page, -1, false);
+@@ -752,8 +760,7 @@ struct page *page_pool_alloc_frag(struct
+ unsigned int max_size = PAGE_SIZE << pool->p.order;
+ struct page *page = pool->frag_page;
+
+- if (WARN_ON(!(pool->p.flags & PP_FLAG_PAGE_FRAG) ||
+- size > max_size))
++ if (WARN_ON(size > max_size))
+ return NULL;
+
+ size = ALIGN(size, dma_get_cache_alignment());
projects / openwrt / staging / nbd.git / commitdiff