mm: page_frag: Introduce page_frag_alloc_align()

In the current implementation of page_frag_alloc(), it doesn't have
any align guarantee for the returned buffer address. But for some
hardwares they do require the DMA buffer to be aligned correctly,
so we would have to use some workarounds like below if the buffers
allocated by the page_frag_alloc() are used by these hardwares for
DMA.
    buf = page_frag_alloc(really_needed_size + align);
    buf = PTR_ALIGN(buf, align);

These codes seems ugly and would waste a lot of memories if the buffers
are used in a network driver for the TX/RX. So introduce
page_frag_alloc_align() to make sure that an aligned buffer address is
returned.

Signed-off-by: Kevin Hao <haokexin@gmail.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Alexander Duyck <alexanderduyck@fb.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/include/linux/gfp.h b/include/linux/gfp.h
index 6e479e9c48cebe6aca409a9d49d98cd3351f1785..80544d5c08e7cf6efc71bec1f32b5f07e7b24b59 100644 (file)
--- a/include/linux/gfp.h
+++ b/include/linux/gfp.h
@@ -583,8 +583,16 @@ extern void free_pages(unsigned long addr, unsigned int order);
 
 struct page_frag_cache;
 extern void __page_frag_cache_drain(struct page *page, unsigned int count);
-extern void *page_frag_alloc(struct page_frag_cache *nc,
-                            unsigned int fragsz, gfp_t gfp_mask);
+extern void *page_frag_alloc_align(struct page_frag_cache *nc,
+                                  unsigned int fragsz, gfp_t gfp_mask,
+                                  unsigned int align_mask);
+
+static inline void *page_frag_alloc(struct page_frag_cache *nc,
+                            unsigned int fragsz, gfp_t gfp_mask)
+{
+       return page_frag_alloc_align(nc, fragsz, gfp_mask, ~0u);
+}
+
 extern void page_frag_free(void *addr);
 
 #define __free_page(page) __free_pages((page), 0)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 519a60d5b6f7d5017c788ced10c9fcca6637dd65..ef5070fed76b97605ddeaae8b8c532ea81d7db54 100644 (file)
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -5137,8 +5137,9 @@ void __page_frag_cache_drain(struct page *page, unsigned int count)
 }
 EXPORT_SYMBOL(__page_frag_cache_drain);
 
-void *page_frag_alloc(struct page_frag_cache *nc,
-                     unsigned int fragsz, gfp_t gfp_mask)
+void *page_frag_alloc_align(struct page_frag_cache *nc,
+                     unsigned int fragsz, gfp_t gfp_mask,
+                     unsigned int align_mask)
 {
        unsigned int size = PAGE_SIZE;
        struct page *page;
@@ -5190,11 +5191,12 @@ refill:
        }
 
        nc->pagecnt_bias--;
+       offset &= align_mask;
        nc->offset = offset;
 
        return nc->va + offset;
 }
-EXPORT_SYMBOL(page_frag_alloc);
+EXPORT_SYMBOL(page_frag_alloc_align);
 
 /*
  * Frees a page fragment allocated out of either a compound or order 0 page.