[PATCH 3/3] percpu: allow select gfp to be passed to underlying allocators

[Dennis Zhou]

The prior patch added support for passing gfp flags through to the
underlying allocators. This patch allows users to pass along gfp flags
(currently only __GFP_NORETRY and __GFP_NOWARN) to the underlying
allocators. This should allow users to decide if they are ok with
failing allocations recovering in a more graceful way.

Additionally, the prior use of gfp was as additional gfp flags that were
then combined with the base flags, namely GFP_KERNEL. gfp_percpu_mask is
introduced to create the base of GFP_KERNEL and whitelist allowed gfp
flags. Using this in the appropriate places changes gfp use from as
additional flags to as a whole set in general removing the need to
always or with the GFP_KERNEL.

Signed-off-by: Dennis Zhou <dennisszhou@xxxxxxxxx>
Suggested-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
---
 mm/percpu-km.c |  2 +-
 mm/percpu-vm.c |  4 ++--
 mm/percpu.c    | 16 ++++++++++------
 3 files changed, 13 insertions(+), 9 deletions(-)

diff --git a/mm/percpu-km.c b/mm/percpu-km.c
index 0d88d7b..38de70a 100644
--- a/mm/percpu-km.c
+++ b/mm/percpu-km.c
@@ -56,7 +56,7 @@ static struct pcpu_chunk *pcpu_create_chunk(gfp_t gfp)
 	if (!chunk)
 		return NULL;
 
-	pages = alloc_pages(gfp | GFP_KERNEL, order_base_2(nr_pages));
+	pages = alloc_pages(gfp, order_base_2(nr_pages));
 	if (!pages) {
 		pcpu_free_chunk(chunk);
 		return NULL;
diff --git a/mm/percpu-vm.c b/mm/percpu-vm.c
index ea9906a..c771d86 100644
--- a/mm/percpu-vm.c
+++ b/mm/percpu-vm.c
@@ -37,7 +37,7 @@ static struct page **pcpu_get_pages(void)
 	lockdep_assert_held(&pcpu_alloc_mutex);
 
 	if (!pages)
-		pages = pcpu_mem_zalloc(pages_size, 0);
+		pages = pcpu_mem_zalloc(pages_size, gfp_percpu_mask(0));
 	return pages;
 }
 
@@ -86,7 +86,7 @@ static int pcpu_alloc_pages(struct pcpu_chunk *chunk,
 	unsigned int cpu, tcpu;
 	int i;
 
-	gfp |=  GFP_KERNEL | __GFP_HIGHMEM;
+	gfp |= __GFP_HIGHMEM;
 
 	for_each_possible_cpu(cpu) {
 		for (i = page_start; i < page_end; i++) {
diff --git a/mm/percpu.c b/mm/percpu.c
index 2489b8b..e35a120 100644
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -91,6 +91,10 @@
 
 #include "percpu-internal.h"
 
+/* the whitelisted flags that can be passed to the backing allocators */
+#define gfp_percpu_mask(gfp) (((gfp) & (__GFP_NORETRY | __GFP_NOWARN)) | \
+			      GFP_KERNEL)
+
 /* the slots are sorted by free bytes left, 1-31 bytes share the same slot */
 #define PCPU_SLOT_BASE_SHIFT		5
 
@@ -466,10 +470,9 @@ static void *pcpu_mem_zalloc(size_t size, gfp_t gfp)
 		return NULL;
 
 	if (size <= PAGE_SIZE)
-		return kzalloc(size, gfp | GFP_KERNEL);
+		return kzalloc(size, gfp);
 	else
-		return __vmalloc(size, gfp | GFP_KERNEL | __GFP_ZERO,
-				 PAGE_KERNEL);
+		return __vmalloc(size, gfp | __GFP_ZERO, PAGE_KERNEL);
 }
 
 /**
@@ -1344,6 +1347,7 @@ static struct pcpu_chunk *pcpu_chunk_addr_search(void *addr)
 static void __percpu *pcpu_alloc(size_t size, size_t align, bool reserved,
 				 gfp_t gfp)
 {
+	gfp_t pcpu_gfp = gfp_percpu_mask(gfp);
 	bool is_atomic = (gfp & GFP_KERNEL) != GFP_KERNEL;
 	bool do_warn = !(gfp & __GFP_NOWARN);
 	static int warn_limit = 10;
@@ -1426,7 +1430,7 @@ static void __percpu *pcpu_alloc(size_t size, size_t align, bool reserved,
 	}
 
 	if (list_empty(&pcpu_slot[pcpu_nr_slots - 1])) {
-		chunk = pcpu_create_chunk(0);
+		chunk = pcpu_create_chunk(pcpu_gfp);
 		if (!chunk) {
 			err = "failed to allocate new chunk";
 			goto fail;
@@ -1455,7 +1459,7 @@ static void __percpu *pcpu_alloc(size_t size, size_t align, bool reserved,
 					   page_start, page_end) {
 			WARN_ON(chunk->immutable);
 
-			ret = pcpu_populate_chunk(chunk, rs, re, 0);
+			ret = pcpu_populate_chunk(chunk, rs, re, pcpu_gfp);
 
 			spin_lock_irqsave(&pcpu_lock, flags);
 			if (ret) {
@@ -1576,7 +1580,7 @@ void __percpu *__alloc_reserved_percpu(size_t size, size_t align)
 static void pcpu_balance_workfn(struct work_struct *work)
 {
 	/* gfp flags passed to underlying allocators */
-	gfp_t gfp = __GFP_NORETRY | __GFP_NOWARN;
+	gfp_t gfp = gfp_percpu_mask(__GFP_NORETRY | __GFP_NOWARN);
 	LIST_HEAD(to_free);
 	struct list_head *free_head = &pcpu_slot[pcpu_nr_slots - 1];
 	struct pcpu_chunk *chunk, *next;
-- 
1.8.3.1