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.
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/mm_types_task.h | 16 +++++-----
include/linux/page_frag_cache.h | 52 +++++++++++++++++++++++++++++++--
mm/page_frag_cache.c | 49 +++++++++++++++++--------------
3 files changed, 85 insertions(+), 32 deletions(-)
diff --git a/include/linux/mm_types_task.h b/include/linux/mm_types_task.h
index b1c54b2b9308..f2610112a642 100644
--- a/include/linux/mm_types_task.h
+++ b/include/linux/mm_types_task.h
@@ -50,18 +50,18 @@ struct page_frag {
#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 page_frag_cache {
- void *va;
-#if (PAGE_SIZE < PAGE_FRAG_CACHE_MAX_SIZE)
+ /* encoded_va consists of the virtual address, pfmemalloc bit and order
+ * of a page.
+ */
+ unsigned long encoded_va;
+
+#if (PAGE_SIZE < PAGE_FRAG_CACHE_MAX_SIZE) && (BITS_PER_LONG <= 32)
__u16 remaining;
- __u16 size;
+ __u16 pagecnt_bias;
#else
__u32 remaining;
+ __u32 pagecnt_bias;
#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;
};
/* Track pages that require TLB flushes */
diff --git a/include/linux/page_frag_cache.h b/include/linux/page_frag_cache.h
index 7c9125a9aed3..4ce924eaf1b1 100644
--- a/include/linux/page_frag_cache.h
+++ b/include/linux/page_frag_cache.h
@@ -3,18 +3,66 @@
#ifndef _LINUX_PAGE_FRAG_CACHE_H
#define _LINUX_PAGE_FRAG_CACHE_H
+#include <linux/bits.h>
+#include <linux/build_bug.h>
#include <linux/log2.h>
#include <linux/types.h>
#include <linux/mm_types_task.h>
+#if (PAGE_SIZE < PAGE_FRAG_CACHE_MAX_SIZE)
+/* Use a full byte here to enable assembler optimization as the shift
+ * operation is usually expecting a byte.
+ */
+#define PAGE_FRAG_CACHE_ORDER_MASK GENMASK(7, 0)
+#define PAGE_FRAG_CACHE_PFMEMALLOC_BIT BIT(8)
+#define PAGE_FRAG_CACHE_PFMEMALLOC_SHIFT 8
+#else
+/* Compiler should be able to figure out we don't read things as any value
+ * ANDed with 0 is 0.
+ */
+#define PAGE_FRAG_CACHE_ORDER_MASK 0
+#define PAGE_FRAG_CACHE_PFMEMALLOC_BIT BIT(0)
+#define PAGE_FRAG_CACHE_PFMEMALLOC_SHIFT 0
+#endif
+
+static inline unsigned long encode_aligned_va(void *va, unsigned int order,
+ bool pfmemalloc)
+{
+ BUILD_BUG_ON(PAGE_FRAG_CACHE_MAX_ORDER > PAGE_FRAG_CACHE_ORDER_MASK);
+ BUILD_BUG_ON(PAGE_FRAG_CACHE_PFMEMALLOC_SHIFT >= PAGE_SHIFT);
+
+ return (unsigned long)va | (order & PAGE_FRAG_CACHE_ORDER_MASK) |
+ ((unsigned long)pfmemalloc << PAGE_FRAG_CACHE_PFMEMALLOC_SHIFT);
+}
+
+static inline unsigned long encoded_page_order(unsigned long encoded_va)
+{
+ return encoded_va & PAGE_FRAG_CACHE_ORDER_MASK;
+}
+
+static inline bool encoded_page_pfmemalloc(unsigned long encoded_va)
+{
+ return !!(encoded_va & PAGE_FRAG_CACHE_PFMEMALLOC_BIT);
+}
+
+static inline void *encoded_page_address(unsigned long encoded_va)
+{
+ return (void *)(encoded_va & PAGE_MASK);
+}
+
static inline void page_frag_cache_init(struct page_frag_cache *nc)
{
- nc->va = NULL;
+ nc->encoded_va = 0;
}
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(unsigned long encoded_va)
+{
+ return PAGE_SIZE << encoded_page_order(encoded_va);
}
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 70fb6dead624..2544b292375a 100644
--- a/mm/page_frag_cache.c
+++ b/mm/page_frag_cache.c
@@ -22,6 +22,7 @@
static struct page *__page_frag_cache_refill(struct page_frag_cache *nc,
gfp_t gfp_mask)
{
+ unsigned long order = PAGE_FRAG_CACHE_MAX_ORDER;
struct page *page = NULL;
gfp_t gfp = gfp_mask;
@@ -30,23 +31,31 @@ 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 = 0;
+ return NULL;
+ }
- nc->va = page ? page_address(page) : NULL;
+ order = 0;
+ }
+
+ 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((void *)nc->encoded_va),
+ nc->pagecnt_bias);
+ nc->encoded_va = 0;
}
EXPORT_SYMBOL(page_frag_cache_drain);
@@ -63,33 +72,29 @@ void *__page_frag_alloc_va_align(struct page_frag_cache *nc,
unsigned int fragsz, gfp_t gfp_mask,
unsigned int align_mask)
{
-#if (PAGE_SIZE < PAGE_FRAG_CACHE_MAX_SIZE)
- unsigned int size = nc->size;
-#else
- unsigned int size = PAGE_SIZE;
-#endif
- unsigned int remaining;
+ unsigned long encoded_va = nc->encoded_va;
+ unsigned int size, remaining;
struct page *page;
- if (unlikely(!nc->va)) {
+ if (unlikely(!encoded_va)) {
refill:
page = __page_frag_cache_refill(nc, gfp_mask);
if (!page)
return NULL;
-#if (PAGE_SIZE < PAGE_FRAG_CACHE_MAX_SIZE)
- /* if size can vary use size else just use PAGE_SIZE */
- size = nc->size;
-#endif
+ encoded_va = nc->encoded_va;
+ size = page_frag_cache_page_size(encoded_va);
+
/* Even if we own the page, we do not use atomic_set().
* This would break get_page_unless_zero() users.
*/
page_ref_add(page, PAGE_FRAG_CACHE_MAX_SIZE);
/* reset page count bias and remaining to start of new frag */
- nc->pfmemalloc = page_is_pfmemalloc(page);
nc->pagecnt_bias = PAGE_FRAG_CACHE_MAX_SIZE + 1;
nc->remaining = size;
+ } else {
+ size = page_frag_cache_page_size(encoded_va);
}
remaining = nc->remaining & align_mask;
@@ -107,13 +112,13 @@ void *__page_frag_alloc_va_align(struct page_frag_cache *nc,
return NULL;
}
- page = virt_to_page(nc->va);
+ page = virt_to_page((void *)encoded_va);
if (!page_ref_sub_and_test(page, nc->pagecnt_bias))
goto refill;
- if (unlikely(nc->pfmemalloc)) {
- free_unref_page(page, compound_order(page));
+ if (unlikely(encoded_page_pfmemalloc(encoded_va))) {
+ free_unref_page(page, encoded_page_order(encoded_va));
goto refill;
}
@@ -128,7 +133,7 @@ void *__page_frag_alloc_va_align(struct page_frag_cache *nc,
nc->pagecnt_bias--;
nc->remaining = remaining - fragsz;
- return nc->va + (size - remaining);
+ return encoded_page_address(encoded_va) + (size - remaining);
}
EXPORT_SYMBOL(__page_frag_alloc_va_align);
--
2.33.0
