Currently there is one 'struct page_frag' for every 'struct sock' and 'struct task_struct', we are about to replace the 'struct page_frag' with 'struct page_frag_cache' for them. Before begin the replacing, we need to ensure the size of 'struct page_frag_cache' is not bigger than the size of 'struct page_frag', as there may be tens of thousands of 'struct sock' and 'struct task_struct' instances in the system. By or'ing the page order & pfmemalloc with lower bits of 'va' instead of using 'u16' or 'u32' for page size and 'u8' for pfmemalloc, we are able to avoid 3 or 5 bytes space waste. And page address & pfmemalloc & order is unchanged for the same page in the same 'page_frag_cache' instance, it makes sense to fit them together. Also, it is better to replace 'offset' with 'remaining', which is the remaining size for the cache in a 'page_frag_cache' instance, we are able to do a single 'fragsz > remaining' checking for the case of cache not being enough, which should be the fast path if we ensure size is zoro when 'va' == NULL by memset'ing 'struct page_frag_cache' in page_frag_cache_init() and page_frag_cache_drain(). After this patch, the size of 'struct page_frag_cache' should be the same as the size of 'struct page_frag'. CC: Alexander Duyck <alexander.duyck@xxxxxxxxx> Signed-off-by: Yunsheng Lin <linyunsheng@xxxxxxxxxx> --- include/linux/page_frag_cache.h | 77 ++++++++++++++++++++++++++++----- mm/page_frag_cache.c | 77 +++++++++++++++++++-------------- 2 files changed, 110 insertions(+), 44 deletions(-) diff --git a/include/linux/page_frag_cache.h b/include/linux/page_frag_cache.h index 024ff73a7ea4..5f9971c1be74 100644 --- a/include/linux/page_frag_cache.h +++ b/include/linux/page_frag_cache.h @@ -8,29 +8,82 @@ #define PAGE_FRAG_CACHE_MAX_SIZE __ALIGN_MASK(32768, ~PAGE_MASK) #define PAGE_FRAG_CACHE_MAX_ORDER get_order(PAGE_FRAG_CACHE_MAX_SIZE) +/* + * struct encoded_va - a nonexistent type marking this pointer + * + * An 'encoded_va' pointer is a pointer to a aligned virtual address, which is + * at least aligned to PAGE_SIZE, that means there are at least 12 lower bits + * space available for other purposes. + * + * Currently we use the lower 8 bits and bit 9 for the order and PFMEMALLOC + * flag of the page this 'va' is corresponding to. + * + * Use the supplied helper functions to endcode/decode the pointer and bits. + */ +struct encoded_va; + +#define PAGE_FRAG_CACHE_ORDER_MASK GENMASK(7, 0) +#define PAGE_FRAG_CACHE_PFMEMALLOC_BIT BIT(8) +#define PAGE_FRAG_CACHE_PFMEMALLOC_SHIFT 8 + +static inline struct encoded_va *encode_aligned_va(void *va, + unsigned int order, + bool pfmemalloc) +{ + return (struct encoded_va *)((unsigned long)va | order | + pfmemalloc << PAGE_FRAG_CACHE_PFMEMALLOC_SHIFT); +} + +static inline unsigned long encoded_page_order(struct encoded_va *encoded_va) +{ + return PAGE_FRAG_CACHE_ORDER_MASK & (unsigned long)encoded_va; +} + +static inline bool encoded_page_pfmemalloc(struct encoded_va *encoded_va) +{ + return PAGE_FRAG_CACHE_PFMEMALLOC_BIT & (unsigned long)encoded_va; +} + +static inline void *encoded_page_address(struct encoded_va *encoded_va) +{ + return (void *)((unsigned long)encoded_va & PAGE_MASK); +} + struct page_frag_cache { - void *va; -#if (PAGE_SIZE < PAGE_FRAG_CACHE_MAX_SIZE) - __u16 offset; - __u16 size; + struct encoded_va *encoded_va; + +#if (PAGE_SIZE < PAGE_FRAG_CACHE_MAX_SIZE) && (BITS_PER_LONG <= 32) + u16 pagecnt_bias; + u16 remaining; #else - __u32 offset; + u32 pagecnt_bias; + u32 remaining; #endif - /* we maintain a pagecount bias, so that we dont dirty cache line - * containing page->_refcount every time we allocate a fragment. - */ - unsigned int pagecnt_bias; - bool pfmemalloc; }; static inline void page_frag_cache_init(struct page_frag_cache *nc) { - nc->va = NULL; + memset(nc, 0, sizeof(*nc)); } static inline bool page_frag_cache_is_pfmemalloc(struct page_frag_cache *nc) { - return !!nc->pfmemalloc; + return encoded_page_pfmemalloc(nc->encoded_va); +} + +static inline unsigned int page_frag_cache_page_size(struct encoded_va *encoded_va) +{ +#if (PAGE_SIZE < PAGE_FRAG_CACHE_MAX_SIZE) + return PAGE_SIZE << encoded_page_order(encoded_va); +#else + return PAGE_SIZE; +#endif +} + +static inline unsigned int __page_frag_cache_page_offset(struct encoded_va *encoded_va, + unsigned int remaining) +{ + return page_frag_cache_page_size(encoded_va) - remaining; } void page_frag_cache_drain(struct page_frag_cache *nc); diff --git a/mm/page_frag_cache.c b/mm/page_frag_cache.c index c0ecfa733727..97cbc2dac67f 100644 --- a/mm/page_frag_cache.c +++ b/mm/page_frag_cache.c @@ -23,6 +23,7 @@ static struct page *__page_frag_cache_refill(struct page_frag_cache *nc, { struct page *page = NULL; gfp_t gfp = gfp_mask; + unsigned int order; #if (PAGE_SIZE < PAGE_FRAG_CACHE_MAX_SIZE) /* Ensure free_unref_page() can be used to free the page fragment */ @@ -32,23 +33,35 @@ static struct page *__page_frag_cache_refill(struct page_frag_cache *nc, __GFP_NOWARN | __GFP_NORETRY | __GFP_NOMEMALLOC; page = alloc_pages_node(NUMA_NO_NODE, gfp_mask, PAGE_FRAG_CACHE_MAX_ORDER); - nc->size = page ? PAGE_FRAG_CACHE_MAX_SIZE : PAGE_SIZE; #endif - if (unlikely(!page)) + if (unlikely(!page)) { page = alloc_pages_node(NUMA_NO_NODE, gfp, 0); + if (unlikely(!page)) { + nc->encoded_va = NULL; + nc->remaining = 0; + return NULL; + } - nc->va = page ? page_address(page) : NULL; + order = 0; + nc->remaining = PAGE_SIZE; + } else { + order = PAGE_FRAG_CACHE_MAX_ORDER; + nc->remaining = PAGE_FRAG_CACHE_MAX_SIZE; + } + nc->encoded_va = encode_aligned_va(page_address(page), order, + page_is_pfmemalloc(page)); return page; } void page_frag_cache_drain(struct page_frag_cache *nc) { - if (!nc->va) + if (!nc->encoded_va) return; - __page_frag_cache_drain(virt_to_head_page(nc->va), nc->pagecnt_bias); - nc->va = NULL; + __page_frag_cache_drain(virt_to_head_page(nc->encoded_va), + nc->pagecnt_bias); + memset(nc, 0, sizeof(*nc)); } EXPORT_SYMBOL(page_frag_cache_drain); @@ -65,10 +78,19 @@ void *__page_frag_alloc_va_align(struct page_frag_cache *nc, unsigned int fragsz, gfp_t gfp_mask, unsigned int align_mask) { - unsigned int size, offset; + struct encoded_va *encoded_va; + unsigned int remaining; struct page *page; - if (unlikely(!nc->va)) { + encoded_va = nc->encoded_va; + if (unlikely(!encoded_va)) { + /* fragsz is not supposed to be bigger than PAGE_SIZE as we are + * allowing order 3 page allocation to fail easily under low + * memory condition. + */ + if (WARN_ON_ONCE(fragsz > PAGE_SIZE)) + return NULL; + refill: page = __page_frag_cache_refill(nc, gfp_mask); if (!page) @@ -79,34 +101,23 @@ void *__page_frag_alloc_va_align(struct page_frag_cache *nc, */ page_ref_add(page, PAGE_FRAG_CACHE_MAX_SIZE); - /* reset page count bias and offset to start of new frag */ - nc->pfmemalloc = page_is_pfmemalloc(page); - nc->pagecnt_bias = PAGE_FRAG_CACHE_MAX_SIZE + 1; - nc->offset = 0; + /* reset page count bias and remaining of new frag */ + nc->pagecnt_bias = PAGE_FRAG_CACHE_MAX_SIZE; + nc->remaining -= fragsz; + return encoded_page_address(nc->encoded_va); } -#if (PAGE_SIZE < PAGE_FRAG_CACHE_MAX_SIZE) - /* if size can vary use size else just use PAGE_SIZE */ - size = nc->size; -#else - size = PAGE_SIZE; -#endif + remaining = nc->remaining & align_mask; - offset = __ALIGN_KERNEL_MASK(nc->offset, ~align_mask); - if (unlikely(offset + fragsz > size)) { - /* fragsz is not supposed to be bigger than PAGE_SIZE as we are - * allowing order 3 page allocation to fail easily under low - * memory condition. - */ + if (unlikely(fragsz > remaining)) { if (WARN_ON_ONCE(fragsz > PAGE_SIZE)) return NULL; - page = virt_to_page(nc->va); - + page = virt_to_page(encoded_va); if (!page_ref_sub_and_test(page, nc->pagecnt_bias)) goto refill; - if (unlikely(nc->pfmemalloc)) { + if (unlikely(encoded_page_pfmemalloc(encoded_va))) { free_unref_page(page, compound_order(page)); goto refill; } @@ -114,15 +125,17 @@ void *__page_frag_alloc_va_align(struct page_frag_cache *nc, /* OK, page count is 0, we can safely set it */ set_page_count(page, PAGE_FRAG_CACHE_MAX_SIZE + 1); - /* reset page count bias and offset to start of new frag */ - nc->pagecnt_bias = PAGE_FRAG_CACHE_MAX_SIZE + 1; - offset = 0; + /* reset page count bias and remaining of new frag */ + nc->pagecnt_bias = PAGE_FRAG_CACHE_MAX_SIZE; + nc->remaining = page_frag_cache_page_size(encoded_va) - fragsz; + return encoded_page_address(nc->encoded_va); } + nc->remaining = remaining - fragsz; nc->pagecnt_bias--; - nc->offset = offset + fragsz; - return nc->va + offset; + return encoded_page_address(encoded_va) + + __page_frag_cache_page_offset(encoded_va, remaining); } EXPORT_SYMBOL(__page_frag_alloc_va_align); -- 2.33.0