netdev - [PATCH v2 1/8] page_frag_cache: Remove pfmemalloc bool

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Date:   Thu, 22 Mar 2018 08:31:50 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Alexander Duyck <alexander.duyck@...il.com>
Cc:     Matthew Wilcox <mawilcox@...rosoft.com>, netdev@...r.kernel.org,
        linux-mm@...ck.org, Jesper Dangaard Brouer <brouer@...hat.com>,
        Eric Dumazet <eric.dumazet@...il.com>
Subject: [PATCH v2 1/8] page_frag_cache: Remove pfmemalloc bool

From: Matthew Wilcox <mawilcox@...rosoft.com>

Save 4/8 bytes by moving the pfmemalloc indicator from its own bool
to the top bit of pagecnt_bias.  This has no effect on the fastpath
of the allocator since the pagecnt_bias cannot go negative.  It's
a couple of extra instructions in the slowpath.

Signed-off-by: Matthew Wilcox <mawilcox@...rosoft.com>
---
 include/linux/mm_types.h | 4 +++-
 mm/page_alloc.c          | 8 +++++---
 net/core/skbuff.c        | 5 ++---
 3 files changed, 10 insertions(+), 7 deletions(-)

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index fd1af6b9591d..a63b138ad1a4 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -218,6 +218,7 @@ struct page {
 
 #define PAGE_FRAG_CACHE_MAX_SIZE	__ALIGN_MASK(32768, ~PAGE_MASK)
 #define PAGE_FRAG_CACHE_MAX_ORDER	get_order(PAGE_FRAG_CACHE_MAX_SIZE)
+#define PFC_MEMALLOC			(1U << 31)
 
 struct page_frag_cache {
 	void * va;
@@ -231,9 +232,10 @@ struct page_frag_cache {
 	 * containing page->_refcount every time we allocate a fragment.
 	 */
 	unsigned int		pagecnt_bias;
-	bool pfmemalloc;
 };
 
+#define page_frag_cache_pfmemalloc(pfc)	((pfc)->pagecnt_bias & PFC_MEMALLOC)
+
 typedef unsigned long vm_flags_t;
 
 /*
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 635d7dd29d7f..61366f23e8c8 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -4395,16 +4395,18 @@ void *page_frag_alloc(struct page_frag_cache *nc,
 		page_ref_add(page, size - 1);
 
 		/* reset page count bias and offset to start of new frag */
-		nc->pfmemalloc = page_is_pfmemalloc(page);
 		nc->pagecnt_bias = size;
+		if (page_is_pfmemalloc(page))
+			nc->pagecnt_bias |= PFC_MEMALLOC;
 		nc->offset = size;
 	}
 
 	offset = nc->offset - fragsz;
 	if (unlikely(offset < 0)) {
+		unsigned int pagecnt_bias = nc->pagecnt_bias & ~PFC_MEMALLOC;
 		page = virt_to_page(nc->va);
 
-		if (!page_ref_sub_and_test(page, nc->pagecnt_bias))
+		if (!page_ref_sub_and_test(page, pagecnt_bias))
 			goto refill;
 
 #if (PAGE_SIZE < PAGE_FRAG_CACHE_MAX_SIZE)
@@ -4415,7 +4417,7 @@ void *page_frag_alloc(struct page_frag_cache *nc,
 		set_page_count(page, size);
 
 		/* reset page count bias and offset to start of new frag */
-		nc->pagecnt_bias = size;
+		nc->pagecnt_bias = size | (nc->pagecnt_bias - pagecnt_bias);
 		offset = size - fragsz;
 	}
 
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 0bb0d8877954..54bbde8f7541 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -412,7 +412,7 @@ struct sk_buff *__netdev_alloc_skb(struct net_device *dev, unsigned int len,
 
 	nc = this_cpu_ptr(&netdev_alloc_cache);
 	data = page_frag_alloc(nc, len, gfp_mask);
-	pfmemalloc = nc->pfmemalloc;
+	pfmemalloc = page_frag_cache_pfmemalloc(nc);
 
 	local_irq_restore(flags);
 
@@ -485,8 +485,7 @@ struct sk_buff *__napi_alloc_skb(struct napi_struct *napi, unsigned int len,
 		return NULL;
 	}
 
-	/* use OR instead of assignment to avoid clearing of bits in mask */
-	if (nc->page.pfmemalloc)
+	if (page_frag_cache_pfmemalloc(&nc->page))
 		skb->pfmemalloc = 1;
 	skb->head_frag = 1;
 
-- 
2.16.2