[PATCH 3/4] percpu: allow non-linear / sparse cpu -> unit mapping

Tejun Heo
2009-06-17T04:26:36Z

Currently cpu and unit are always identity mapped. To allow more
efficient large page support on NUMA and lazy allocation for possible
but offline cpus, cpu -> unit mapping needs to be non-linear and/or
sparse. This can be easily implemented by adding a cpu -> unit
mapping array and using it whenever looking up the matching unit for a
cpu.

The only unusal conversion is in pcpu_chunk_addr_search(). The passed
in address is unit0 based and unit0 might not be in use so it needs to
be converted to address of an in-use unit. This is easily done by
adding the unit offset for the current processor.

[ Impact: allows non-linear/sparse cpu -> unit mapping, no visible change yet ]

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Ingo Molnar <mingo@elte.hu>
---
include/linux/percpu.h | 3 +-
mm/percpu.c | 129 +++++++++++++++++++++++++++++++++++-------------
2 files changed, 96 insertions(+), 36 deletions(-)

diff --git a/include/linux/percpu.h b/include/linux/percpu.h
index 63c8b7a..1e0e887 100644
--- a/include/linux/percpu.h
+++ b/include/linux/percpu.h
@@ -57,6 +57,7 @@
#endif

extern void *pcpu_base_addr;
+extern const int *pcpu_unit_map;

typedef void * (*pcpu_fc_alloc_fn_t)(unsigned int cpu, size_t size);
typedef void (*pcpu_fc_free_fn_t)(void *ptr, size_t size);
@@ -66,7 +67,7 @@ typedef void (*pcpu_fc_map_fn_t)(void *ptr, size_t size, void *addr);
extern size_t __init pcpu_setup_first_chunk(
size_t static_size, size_t reserved_size,
ssize_t dyn_size, size_t unit_size,
- void *base_addr);
+ void *base_addr, const int *unit_map);

extern ssize_t __init pcpu_embed_first_chunk(
size_t static_size, size_t reserved_size,
diff --git a/mm/percpu.c b/mm/percpu.c
index 5ee712e..f0fce38 100644
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -8,12 +8,13 @@
*
* This is percpu allocator which can handle both static and dynamic
* areas. Percpu areas are allocated in chunks in vmalloc area. Each
- * chunk is consisted of num_possible_cpus() units and the first chunk
- * is used for static percpu variables in the kernel image (special
- * boot time alloc/init handling necessary as these areas need to be
- * brought up before allocation services are running). Unit grows as
- * necessary and all units grow or shrink in unison. When a chunk is
- * filled up, another chunk is allocated. ie. in vmalloc area
+ * chunk is consisted of boot-time determined number of units and the
+ * first chunk is used for static percpu variables in the kernel image
+ * (special boot time alloc/init handling necessary as these areas
+ * need to be brought up before allocation services are running).
+ * Unit grows as necessary and all units grow or shrink in unison.
+ * When a chunk is filled up, another chunk is allocated. ie. in
+ * vmalloc area
*
* c0 c1 c2
* ------------------- ------------------- ------------
@@ -22,11 +23,13 @@
*
* Allocation is done in offset-size areas of single unit space. Ie,
* an area of 512 bytes at 6k in c1 occupies 512 bytes at 6k of c1:u0,
- * c1:u1, c1:u2 and c1:u3. Percpu access can be done by configuring
- * percpu base registers pcpu_unit_size apart.
+ * c1:u1, c1:u2 and c1:u3. On UMA, units corresponds directly to
+ * cpus. On NUMA, the mapping can be non-linear and even sparse.
+ * Percpu access can be done by configuring percpu base registers
+ * according to cpu to unit mapping and pcpu_unit_size.
*
- * There are usually many small percpu allocations many of them as
- * small as 4 bytes. The allocator organizes chunks into lists
+ * There are usually many small percpu allocations many of them being
+ * as small as 4 bytes. The allocator organizes chunks into lists
* according to free size and tries to allocate from the fullest one.
* Each chunk keeps the maximum contiguous area size hint which is
* guaranteed to be eqaul to or larger than the maximum contiguous
@@ -99,14 +102,22 @@ struct pcpu_chunk {

static int pcpu_unit_pages __read_mostly;
static int pcpu_unit_size __read_mostly;
+static int pcpu_nr_units __read_mostly;
static int pcpu_chunk_size __read_mostly;
static int pcpu_nr_slots __read_mostly;
static size_t pcpu_chunk_struct_size __read_mostly;

+/* cpus with the lowest and highest unit numbers */
+static unsigned int pcpu_first_unit_cpu __read_mostly;
+static unsigned int pcpu_last_unit_cpu __read_mostly;
+
/* the address of the first chunk which starts with the kernel static area */
void *pcpu_base_addr __read_mostly;
EXPORT_SYMBOL_GPL(pcpu_base_addr);

+/* cpu -> unit map */
+const int *pcpu_unit_map __read_mostly;
+
/*
* The first chunk which always exists. Note that unlike other
* chunks, this one can be allocated and mapped in several different
@@ -177,7 +188,7 @@ static int pcpu_chunk_slot(const struct pcpu_chunk *chunk)

static int pcpu_page_idx(unsigned int cpu, int page_idx)
{
- return cpu * pcpu_unit_pages + page_idx;
+ return pcpu_unit_map[cpu] * pcpu_unit_pages + page_idx;
}

static unsigned long pcpu_chunk_addr(struct pcpu_chunk *chunk,
@@ -321,6 +332,14 @@ static struct pcpu_chunk *pcpu_chunk_addr_search(void *addr)
return pcpu_first_chunk;
}

+ /*
+ * The address is relative to unit0 which might be unused and
+ * thus unmapped. Offset the address to the unit space of the
+ * current processor before looking it up in the vmalloc
+ * space. Note that any possible cpu id can be used here, so
+ * there's no need to worry about preemption or cpu hotplug.
+ */
+ addr += pcpu_unit_map[smp_processor_id()] * pcpu_unit_size;
return pcpu_get_page_chunk(vmalloc_to_page(addr));
}

@@ -593,8 +612,7 @@ static struct page **pcpu_get_pages_and_bitmap(struct pcpu_chunk *chunk,
{
static struct page **pages;
static unsigned long *bitmap;
- size_t pages_size = num_possible_cpus() * pcpu_unit_pages *
- sizeof(pages[0]);
+ size_t pages_size = pcpu_nr_units * pcpu_unit_pages * sizeof(pages[0]);
size_t bitmap_size = BITS_TO_LONGS(pcpu_unit_pages) *
sizeof(unsigned long);

@@ -692,10 +710,9 @@ static int pcpu_alloc_pages(struct pcpu_chunk *chunk,
static void pcpu_pre_unmap_flush(struct pcpu_chunk *chunk,
int page_start, int page_end)
{
- unsigned int last = num_possible_cpus() - 1;
-
- flush_cache_vunmap(pcpu_chunk_addr(chunk, 0, page_start),
- pcpu_chunk_addr(chunk, last, page_end));
+ flush_cache_vunmap(
+ pcpu_chunk_addr(chunk, pcpu_first_unit_cpu, page_start),
+ pcpu_chunk_addr(chunk, pcpu_last_unit_cpu, page_end));
}

static void __pcpu_unmap_pages(unsigned long addr, int nr_pages)
@@ -756,10 +773,9 @@ static void pcpu_unmap_pages(struct pcpu_chunk *chunk,
static void pcpu_post_unmap_tlb_flush(struct pcpu_chunk *chunk,
int page_start, int page_end)
{
- unsigned int last = num_possible_cpus() - 1;
-
- flush_tlb_kernel_range(pcpu_chunk_addr(chunk, 0, page_start),
- pcpu_chunk_addr(chunk, last, page_end));
+ flush_tlb_kernel_range(
+ pcpu_chunk_addr(chunk, pcpu_first_unit_cpu, page_start),
+ pcpu_chunk_addr(chunk, pcpu_last_unit_cpu, page_end));
}

static int __pcpu_map_pages(unsigned long addr, struct page **pages,
@@ -835,11 +851,9 @@ err:
static void pcpu_post_map_flush(struct pcpu_chunk *chunk,
int page_start, int page_end)
{
- unsigned int last = num_possible_cpus() - 1;
-
- /* flush at once, please read comments in pcpu_unmap() */
- flush_cache_vmap(pcpu_chunk_addr(chunk, 0, page_start),
- pcpu_chunk_addr(chunk, last, page_end));
+ flush_cache_vmap(
+ pcpu_chunk_addr(chunk, pcpu_first_unit_cpu, page_start),
+ pcpu_chunk_addr(chunk, pcpu_last_unit_cpu, page_end));
}

/**
@@ -953,8 +967,7 @@ static int pcpu_populate_chunk(struct pcpu_chunk *chunk, int off, int size)
bitmap_copy(chunk->populated, populated, pcpu_unit_pages);
clear:
for_each_possible_cpu(cpu)
- memset(chunk->vm->addr + cpu * pcpu_unit_size + off, 0,
- size);
+ memset((void *)pcpu_chunk_addr(chunk, cpu, 0) + off, 0, size);
return 0;

err_unmap:
@@ -1088,6 +1101,7 @@ area_found:

mutex_unlock(&pcpu_alloc_mutex);

+ /* return address relative to unit0 */
return __addr_to_pcpu_ptr(chunk->vm->addr + off);

fail_unlock:
@@ -1222,6 +1236,7 @@ EXPORT_SYMBOL_GPL(free_percpu);
* @dyn_size: free size for dynamic allocation in bytes, -1 for auto
* @unit_size: unit size in bytes, must be multiple of PAGE_SIZE
* @base_addr: mapped address
+ * @unit_map: cpu -> unit map, NULL for sequential mapping
*
* Initialize the first percpu chunk which contains the kernel static
* perpcu area. This function is to be called from arch percpu area
@@ -1260,16 +1275,17 @@ EXPORT_SYMBOL_GPL(free_percpu);
*/
size_t __init pcpu_setup_first_chunk(size_t static_size, size_t reserved_size,
ssize_t dyn_size, size_t unit_size,
- void *base_addr)
+ void *base_addr, const int *unit_map)
{
static struct vm_struct first_vm;
static int smap[2], dmap[2];
size_t size_sum = static_size + reserved_size +
(dyn_size >= 0 ? dyn_size : 0);
struct pcpu_chunk *schunk, *dchunk = NULL;
+ unsigned int cpu, tcpu;
int i;

- /* santiy checks */
+ /* sanity checks */
BUILD_BUG_ON(ARRAY_SIZE(smap) >= PCPU_DFL_MAP_ALLOC ||
ARRAY_SIZE(dmap) >= PCPU_DFL_MAP_ALLOC);
BUG_ON(!static_size);
@@ -1278,9 +1294,52 @@ size_t __init pcpu_setup_first_chunk(size_t static_size, size_t reserved_size,
BUG_ON(unit_size & ~PAGE_MASK);
BUG_ON(unit_size < PCPU_MIN_UNIT_SIZE);

+ /* determine number of units and verify and initialize pcpu_unit_map */
+ if (unit_map) {
+ int first_unit = INT_MAX, last_unit = INT_MIN;
+
+ for_each_possible_cpu(cpu) {
+ int unit = unit_map[cpu];
+
+ BUG_ON(unit < 0);
+ for_each_possible_cpu(tcpu) {
+ if (tcpu == cpu)
+ break;
+ /* the mapping should be one-to-one */
+ BUG_ON(unit_map[tcpu] == unit);
+ }
+
+ if (unit < first_unit) {
+ pcpu_first_unit_cpu = cpu;
+ first_unit = unit;
+ }
+ if (unit > last_unit) {
+ pcpu_last_unit_cpu = cpu;
+ last_unit = unit;
+ }
+ }
+ pcpu_nr_units = last_unit + 1;
+ pcpu_unit_map = unit_map;
+ } else {
+ int *identity_map;
+
+ /* #units == #cpus, identity mapped */
+ identity_map = alloc_bootmem(num_possible_cpus() *
+ sizeof(identity_map[0]));
+
+ for_each_possible_cpu(cpu)
+ identity_map[cpu] = cpu;
+
+ pcpu_first_unit_cpu = 0;
+ pcpu_last_unit_cpu = pcpu_nr_units - 1;
+ pcpu_nr_units = num_possible_cpus();
+ pcpu_unit_map = identity_map;
+ }
+
+ /* determine basic parameters */
pcpu_unit_pages = unit_size >> PAGE_SHIFT;
pcpu_unit_size = pcpu_unit_pages << PAGE_SHIFT;
- pcpu_chunk_size = num_possible_cpus() * pcpu_unit_size;
+ pcpu_chunk_size = pcpu_nr_units * pcpu_unit_size;
pcpu_chunk_struct_size = sizeof(struct pcpu_chunk) +
BITS_TO_LONGS(pcpu_unit_pages) * sizeof(unsigned long);

@@ -1349,7 +1408,7 @@ size_t __init pcpu_setup_first_chunk(size_t static_size, size_t reserved_size,
pcpu_chunk_relocate(pcpu_first_chunk, -1);

/* we're done */
- pcpu_base_addr = (void *)pcpu_chunk_addr(schunk, 0, 0);
+ pcpu_base_addr = schunk->vm->addr;
return pcpu_unit_size;
}

@@ -1427,7 +1486,7 @@ ssize_t __init pcpu_embed_first_chunk(size_t static_size, size_t reserved_size,
size_sum >> PAGE_SHIFT, base, static_size);

return pcpu_setup_first_chunk(static_size, reserved_size, dyn_size,
- unit_size, base);
+ unit_size, base, NULL);
}

/**
@@ -1519,7 +1578,7 @@ ssize_t __init pcpu_4k_first_chunk(size_t static_size, size_t reserved_size,
unit_pages, static_size);

ret = pcpu_setup_first_chunk(static_size, reserved_size, -1,
- unit_pages << PAGE_SHIFT, vm.addr);
+ unit_pages << PAGE_SHIFT, vm.addr, NULL);
goto out_free_ar;

enomem:
@@ -1641,7 +1700,7 @@ ssize_t __init pcpu_lpage_first_chunk(size_t static_size, size_t reserved_size,
"%zu bytes\n", pcpul_vm.addr, static_size);

ret = pcpu_setup_first_chunk(static_size, reserved_size, dyn_size,
- pcpul_unit_size, pcpul_vm.addr);
+ pcpul_unit_size, pcpul_vm.addr, NULL);

/* sort pcpul_map array for pcpu_lpage_remapped() */
for (i = 0; i < num_possible_cpus() - 1; i++)
--
1.6.0.2