3 files changed, 65 insertions, 23 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 08def8deb5f5..ecad946920d1 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1882,6 +1882,12 @@ and is between 256 and 4096 characters. It is defined in the file
                         Format: { 0 | 1 }
                         See arch/parisc/kernel/pdc_chassis.c
 
+        percpu_alloc=   [X86] Select which percpu first chunk allocator to use.
+                        Allowed values are one of "lpage", "embed" and "4k".
+                        See comments in arch/x86/kernel/setup_percpu.c for
+                        details on each allocator.  This parameter is primarily
+                        for debugging and performance comparison.
+
         pf.             [PARIDE]
                         See Documentation/blockdev/paride.txt.
 
diff --git a/arch/x86/kernel/setup_percpu.c b/arch/x86/kernel/setup_percpu.c
index bad2fd223114..165ebd5ba83b 100644
--- a/arch/x86/kernel/setup_percpu.c
+++ b/arch/x86/kernel/setup_percpu.c
@@ -156,20 +156,23 @@ static struct page * __init pcpul_get_page(unsigned int cpu, int pageno)
         return virt_to_page(pcpul_map[cpu].ptr + off);
 }
 
-static ssize_t __init setup_pcpu_lpage(size_t static_size)
+static ssize_t __init setup_pcpu_lpage(size_t static_size, bool chosen)
 {
         size_t map_size, dyn_size;
         unsigned int cpu;
         int i, j;
         ssize_t ret;
 
-        /*
-         * If large page isn't supported, there's no benefit in doing
-         * this.  Also, on non-NUMA, embedding is better.
-         */
-        if (!cpu_has_pse || !pcpu_need_numa())
+        /* on non-NUMA, embedding is better */
+        if (!chosen && !pcpu_need_numa())
                 return -EINVAL;
 
+        /* need PSE */
+        if (!cpu_has_pse) {
+                pr_warning("PERCPU: lpage allocator requires PSE\n");
+                return -EINVAL;
+        }
+
         /*
          * Currently supports only single page.  Supporting multiple
          * pages won't be too difficult if it ever becomes necessary.
@@ -191,8 +194,11 @@ static ssize_t __init setup_pcpu_lpage(size_t static_size)
                 pcpul_map[cpu].cpu = cpu;
                 pcpul_map[cpu].ptr = pcpu_alloc_bootmem(cpu, PMD_SIZE,
                                                         PMD_SIZE);
-                if (!pcpul_map[cpu].ptr)
+                if (!pcpul_map[cpu].ptr) {
+                        pr_warning("PERCPU: failed to allocate large page "
+                                   "for cpu%u\n", cpu);
                         goto enomem;
+                }
 
                 /*
                  * Only use pcpul_size bytes and give back the rest.
@@ -297,7 +303,7 @@ void *pcpu_lpage_remapped(void *kaddr)
         return NULL;
 }
 #else
-static ssize_t __init setup_pcpu_lpage(size_t static_size)
+static ssize_t __init setup_pcpu_lpage(size_t static_size, bool chosen)
 {
         return -EINVAL;
 }
@@ -311,7 +317,7 @@ static ssize_t __init setup_pcpu_lpage(size_t static_size)
  * mapping so that it can use PMD mapping without additional TLB
  * pressure.
  */
-static ssize_t __init setup_pcpu_embed(size_t static_size)
+static ssize_t __init setup_pcpu_embed(size_t static_size, bool chosen)
 {
         size_t reserve = PERCPU_MODULE_RESERVE + PERCPU_DYNAMIC_RESERVE;
 
@@ -320,7 +326,7 @@ static ssize_t __init setup_pcpu_embed(size_t static_size)
          * this.  Also, embedding allocation doesn't play well with
          * NUMA.
          */
-        if (!cpu_has_pse || pcpu_need_numa())
+        if (!chosen && (!cpu_has_pse || pcpu_need_numa()))
                 return -EINVAL;
 
         return pcpu_embed_first_chunk(static_size, PERCPU_FIRST_CHUNK_RESERVE,
@@ -370,8 +376,11 @@ static ssize_t __init setup_pcpu_4k(size_t static_size)
                         void *ptr;
 
                         ptr = pcpu_alloc_bootmem(cpu, PAGE_SIZE, PAGE_SIZE);
-                        if (!ptr)
+                        if (!ptr) {
+                                pr_warning("PERCPU: failed to allocate "
+                                           "4k page for cpu%u\n", cpu);
                                 goto enomem;
+                        }
 
                         memcpy(ptr, __per_cpu_load + i * PAGE_SIZE, PAGE_SIZE);
                         pcpu4k_pages[j++] = virt_to_page(ptr);
@@ -395,6 +404,16 @@ out_free_ar:
         return ret;
 }
 
+/* for explicit first chunk allocator selection */
+static char pcpu_chosen_alloc[16] __initdata;
+
+static int __init percpu_alloc_setup(char *str)
+{
+        strncpy(pcpu_chosen_alloc, str, sizeof(pcpu_chosen_alloc) - 1);
+        return 0;
+}
+early_param("percpu_alloc", percpu_alloc_setup);
+
 static inline void setup_percpu_segment(int cpu)
 {
 #ifdef CONFIG_X86_32
@@ -408,11 +427,6 @@ static inline void setup_percpu_segment(int cpu)
 #endif
 }
 
-/*
- * Great future plan:
- * Declare PDA itself and support (irqstack,tss,pgd) as per cpu data.
- * Always point %gs to its beginning
- */
 void __init setup_per_cpu_areas(void)
 {
         size_t static_size = __per_cpu_end - __per_cpu_start;
@@ -429,9 +443,26 @@ void __init setup_per_cpu_areas(void)
          * of large page mappings.  Please read comments on top of
          * each allocator for details.
          */
-        ret = setup_pcpu_lpage(static_size);
-        if (ret < 0)
-                ret = setup_pcpu_embed(static_size);
+        ret = -EINVAL;
+        if (strlen(pcpu_chosen_alloc)) {
+                if (strcmp(pcpu_chosen_alloc, "4k")) {
+                        if (!strcmp(pcpu_chosen_alloc, "lpage"))
+                                ret = setup_pcpu_lpage(static_size, true);
+                        else if (!strcmp(pcpu_chosen_alloc, "embed"))
+                                ret = setup_pcpu_embed(static_size, true);
+                        else
+                                pr_warning("PERCPU: unknown allocator %s "
+                                           "specified\n", pcpu_chosen_alloc);
+                        if (ret < 0)
+                                pr_warning("PERCPU: %s allocator failed (%zd), "
+                                           "falling back to 4k\n",
+                                           pcpu_chosen_alloc, ret);
+                }
+        } else {
+                ret = setup_pcpu_lpage(static_size, false);
+                if (ret < 0)
+                        ret = setup_pcpu_embed(static_size, false);
+        }
         if (ret < 0)
                 ret = setup_pcpu_4k(static_size);
         if (ret < 0)
diff --git a/mm/percpu.c b/mm/percpu.c
index d06f4748271e..b70f2acd8853 100644
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -1233,6 +1233,7 @@ static struct page * __init pcpue_get_page(unsigned int cpu, int pageno)
 ssize_t __init pcpu_embed_first_chunk(size_t static_size, size_t reserved_size,
                                       ssize_t dyn_size, ssize_t unit_size)
 {
+        size_t chunk_size;
         unsigned int cpu;
 
         /* determine parameters and allocate */
@@ -1247,11 +1248,15 @@ ssize_t __init pcpu_embed_first_chunk(size_t static_size, size_t reserved_size,
         } else
                 pcpue_unit_size = max_t(size_t, pcpue_size, PCPU_MIN_UNIT_SIZE);
 
-        pcpue_ptr = __alloc_bootmem_nopanic(
-                                        num_possible_cpus() * pcpue_unit_size,
-                                        PAGE_SIZE, __pa(MAX_DMA_ADDRESS));
-        if (!pcpue_ptr)
+        chunk_size = pcpue_unit_size * num_possible_cpus();
+
+        pcpue_ptr = __alloc_bootmem_nopanic(chunk_size, PAGE_SIZE,
+                                            __pa(MAX_DMA_ADDRESS));
+        if (!pcpue_ptr) {
+                pr_warning("PERCPU: failed to allocate %zu bytes for "
+                           "embedding\n", chunk_size);
                 return -ENOMEM;
+        }
 
         /* return the leftover and copy */
         for_each_possible_cpu(cpu) {