[...]
+static inline bool page_pool_set_dma_addr(struct page *page, dma_addr_t addr) {
if (WARN_ON(addr & ~PAGE_MASK))return false;page->dma_addr[0] = addr; if (sizeof(dma_addr_t) > sizeof(unsigned long)) page->dma_addr[1] = upper_32_bits(addr);return true;+}
Rather than making this a part of the check here it might make more sense to pull this out and perform the WARN_ON after the check for dma_mapping_error.
I need to point out that I don't like WARN_ON and BUG_ON code in fast-path code, because compiler adds 'ud2' assembler instructions that influences the instruction-cache fetching in the CPU. Yes, I have seen a measuresable impact from this before.
Also it occurs to me that we only really have to do this in the case where dma_addr_t is larger than the size of a long. Otherwise we could just have the code split things so that dma_addr[0] is the dma_addr and dma_addr[1] is our pagecnt_bias value in which case we could probably just skip the check.
The dance to get 64-bit DMA addr on 32-bit systems is rather ugly and confusing, sadly. We could take advantage of this, I just hope this will not make it uglier.
Note here that we can only use this because dma_addr is not aliased to compound page anymore (after the initial page_pool recycling patchset). We must keep this in mind if we even restructure struct page.
Can we do something more radical for this? The 64/32 bit dance is only there for 32 bit systems with 64 bit dma. Since the last time we asked about this no one seemed to care about these, and I really doubt we'll get an ethernet driver for them (that needs recycling....), can we *only* support frag allocation and recycling for 'normal' systems? We could always just r e-purpose dma_addr[1] for those.
Regards /Ilias
+static inline int page_pool_get_pagecnt_bias(struct page *page) +{
return READ_ONCE(page->dma_addr[0]) & ~PAGE_MASK;+}
+static inline unsigned long *page_pool_pagecnt_bias_ptr(struct page *page) +{
return page->dma_addr;+}
+static inline void page_pool_set_pagecnt_bias(struct page *page, int bias) +{
unsigned long dma_addr_0 = READ_ONCE(page->dma_addr[0]);dma_addr_0 &= PAGE_MASK;dma_addr_0 |= bias;WRITE_ONCE(page->dma_addr[0], dma_addr_0);}
static inline bool is_page_pool_compiled_in(void)
diff --git a/net/core/page_pool.c b/net/core/page_pool.c index 78838c6..1abefc6 100644 --- a/net/core/page_pool.c +++ b/net/core/page_pool.c @@ -198,7 +198,13 @@ static bool page_pool_dma_map(struct page_pool *pool, struct page *page) if (dma_mapping_error(pool->p.dev, dma)) return false;
So instead of adding to the function below you could just add your WARN_ON check here with the unmapping call.
page_pool_set_dma_addr(page, dma);
if (unlikely(!page_pool_set_dma_addr(page, dma))) {dma_unmap_page_attrs(pool->p.dev, dma,PAGE_SIZE << pool->p.order,pool->p.dma_dir,DMA_ATTR_SKIP_CPU_SYNC);return false;} if (pool->p.flags & PP_FLAG_DMA_SYNC_DEV) page_pool_dma_sync_for_device(pool, page, pool->p.max_len);-- 2.7.4