diff options
| -rw-r--r-- | mm/percpu.c | 161 |
1 files changed, 124 insertions, 37 deletions
diff --git a/mm/percpu.c b/mm/percpu.c index 4c8a419..bfe6a3a 100644 --- a/mm/percpu.c +++ b/mm/percpu.c @@ -62,6 +62,7 @@ #include <linux/pfn.h> #include <linux/rbtree.h> #include <linux/slab.h> +#include <linux/spinlock.h> #include <linux/vmalloc.h> #include <linux/workqueue.h> @@ -101,20 +102,28 @@ static struct pcpu_chunk *pcpu_reserved_chunk; static int pcpu_reserved_chunk_limit; /* - * One mutex to rule them all. - * - * The following mutex is grabbed in the outermost public alloc/free - * interface functions and released only when the operation is - * complete. As such, every function in this file other than the - * outermost functions are called under pcpu_mutex. - * - * It can easily be switched to use spinlock such that only the area - * allocation and page population commit are protected with it doing - * actual [de]allocation without holding any lock. However, given - * what this allocator does, I think it's better to let them run - * sequentially. + * Synchronization rules. + * + * There are two locks - pcpu_alloc_mutex and pcpu_lock. The former + * protects allocation/reclaim paths, chunks and chunk->page arrays. + * The latter is a spinlock and protects the index data structures - + * chunk slots, rbtree, chunks and area maps in chunks. + * + * During allocation, pcpu_alloc_mutex is kept locked all the time and + * pcpu_lock is grabbed and released as necessary. All actual memory + * allocations are done using GFP_KERNEL with pcpu_lock released. + * + * Free path accesses and alters only the index data structures, so it + * can be safely called from atomic context. When memory needs to be + * returned to the system, free path schedules reclaim_work which + * grabs both pcpu_alloc_mutex and pcpu_lock, unlinks chunks to be + * reclaimed, release both locks and frees the chunks. Note that it's + * necessary to grab both locks to remove a chunk from circulation as + * allocation path might be referencing the chunk with only + * pcpu_alloc_mutex locked. */ -static DEFINE_MUTEX(pcpu_mutex); +static DEFINE_MUTEX(pcpu_alloc_mutex); /* protects whole alloc and reclaim */ +static DEFINE_SPINLOCK(pcpu_lock); /* protects index data structures */ static struct list_head *pcpu_slot __read_mostly; /* chunk list slots */ static struct rb_root pcpu_addr_root = RB_ROOT; /* chunks by address */ @@ -176,6 +185,9 @@ static bool pcpu_chunk_page_occupied(struct pcpu_chunk *chunk, * kzalloc() is used; otherwise, vmalloc() is used. The returned * memory is always zeroed. * + * CONTEXT: + * Does GFP_KERNEL allocation. + * * RETURNS: * Pointer to the allocated area on success, NULL on failure. */ @@ -215,6 +227,9 @@ static void pcpu_mem_free(void *ptr, size_t size) * New slot according to the changed state is determined and @chunk is * moved to the slot. Note that the reserved chunk is never put on * chunk slots. + * + * CONTEXT: + * pcpu_lock. */ static void pcpu_chunk_relocate(struct pcpu_chunk *chunk, int oslot) { @@ -260,6 +275,9 @@ static struct rb_node **pcpu_chunk_rb_search(void *addr, * searchs for the chunk with the highest start address which isn't * beyond @addr. * + * CONTEXT: + * pcpu_lock. + * * RETURNS: * The address of the found chunk. */ @@ -300,6 +318,9 @@ static struct pcpu_chunk *pcpu_chunk_addr_search(void *addr) * @new: chunk to insert * * Insert @new into address rb tree. + * + * CONTEXT: + * pcpu_lock. */ static void pcpu_chunk_addr_insert(struct pcpu_chunk *new) { @@ -319,6 +340,10 @@ static void pcpu_chunk_addr_insert(struct pcpu_chunk *new) * A single allocation can split an area into three areas, so this * function makes sure that @chunk->map has at least two extra slots. * + * CONTEXT: + * pcpu_alloc_mutex, pcpu_lock. pcpu_lock is released and reacquired + * if area map is extended. + * * RETURNS: * 0 if noop, 1 if successfully extended, -errno on failure. */ @@ -332,13 +357,25 @@ static int pcpu_extend_area_map(struct pcpu_chunk *chunk) if (chunk->map_alloc >= chunk->map_used + 2) return 0; + spin_unlock_irq(&pcpu_lock); + new_alloc = PCPU_DFL_MAP_ALLOC; while (new_alloc < chunk->map_used + 2) new_alloc *= 2; new = pcpu_mem_alloc(new_alloc * sizeof(new[0])); - if (!new) + if (!new) { + spin_lock_irq(&pcpu_lock); return -ENOMEM; + } + + /* + * Acquire pcpu_lock and switch to new area map. Only free + * could have happened inbetween, so map_used couldn't have + * grown. + */ + spin_lock_irq(&pcpu_lock); + BUG_ON(new_alloc < chunk->map_used + 2); size = chunk->map_alloc * sizeof(chunk->map[0]); memcpy(new, chunk->map, size); @@ -371,6 +408,9 @@ static int pcpu_extend_area_map(struct pcpu_chunk *chunk) * is inserted after the target block. * * @chunk->map must have enough free slots to accomodate the split. + * + * CONTEXT: + * pcpu_lock. */ static void pcpu_split_block(struct pcpu_chunk *chunk, int i, int head, int tail) @@ -406,6 +446,9 @@ static void pcpu_split_block(struct pcpu_chunk *chunk, int i, * * @chunk->map must have at least two free slots. * + * CONTEXT: + * pcpu_lock. + * * RETURNS: * Allocated offset in @chunk on success, -1 if no matching area is * found. @@ -495,6 +538,9 @@ static int pcpu_alloc_area(struct pcpu_chunk *chunk, int size, int align) * Free area starting from @freeme to @chunk. Note that this function * only modifies the allocation map. It doesn't depopulate or unmap * the area. + * + * CONTEXT: + * pcpu_lock. */ static void pcpu_free_area(struct pcpu_chunk *chunk, int freeme) { @@ -580,6 +626,9 @@ static void pcpu_unmap(struct pcpu_chunk *chunk, int page_start, int page_end, * For each cpu, depopulate and unmap pages [@page_start,@page_end) * from @chunk. If @flush is true, vcache is flushed before unmapping * and tlb after. + * + * CONTEXT: + * pcpu_alloc_mutex. */ static void pcpu_depopulate_chunk(struct pcpu_chunk *chunk, int off, int size, bool flush) @@ -658,6 +707,9 @@ static int pcpu_map(struct pcpu_chunk *chunk, int page_start, int page_end) * * For each cpu, populate and map pages [@page_start,@page_end) into * @chunk. The area is cleared on return. + * + * CONTEXT: + * pcpu_alloc_mutex, does GFP_KERNEL allocation. */ static int pcpu_populate_chunk(struct pcpu_chunk *chunk, int off, int size) { @@ -748,15 +800,16 @@ static struct pcpu_chunk *alloc_pcpu_chunk(void) * @align: alignment of area (max PAGE_SIZE) * @reserved: allocate from the reserved chunk if available * - * Allocate percpu area of @size bytes aligned at @align. Might - * sleep. Might trigger writeouts. + * Allocate percpu area of @size bytes aligned at @align. + * + * CONTEXT: + * Does GFP_KERNEL allocation. * * RETURNS: * Percpu pointer to the allocated area on success, NULL on failure. */ static void *pcpu_alloc(size_t size, size_t align, bool reserved) { - void *ptr = NULL; struct pcpu_chunk *chunk; int slot, off; @@ -766,27 +819,37 @@ static void *pcpu_alloc(size_t size, size_t align, bool reserved) return NULL; } - mutex_lock(&pcpu_mutex); + mutex_lock(&pcpu_alloc_mutex); + spin_lock_irq(&pcpu_lock); /* serve reserved allocations from the reserved chunk if available */ if (reserved && pcpu_reserved_chunk) { chunk = pcpu_reserved_chunk; if (size > chunk->contig_hint || pcpu_extend_area_map(chunk) < 0) - goto out_unlock; + goto fail_unlock; off = pcpu_alloc_area(chunk, size, align); if (off >= 0) goto area_found; - goto out_unlock; + goto fail_unlock; } +restart: /* search through normal chunks */ for (slot = pcpu_size_to_slot(size); slot < pcpu_nr_slots; slot++) { list_for_each_entry(chunk, &pcpu_slot[slot], list) { if (size > chunk->contig_hint) continue; - if (pcpu_extend_area_map(chunk) < 0) - goto out_unlock; + + switch (pcpu_extend_area_map(chunk)) { + case 0: + break; + case 1: + goto restart; /* pcpu_lock dropped, restart */ + default: + goto fail_unlock; + } + off = pcpu_alloc_area(chunk, size, align); if (off >= 0) goto area_found; @@ -794,27 +857,36 @@ static void *pcpu_alloc(size_t size, size_t align, bool reserved) } /* hmmm... no space left, create a new chunk */ + spin_unlock_irq(&pcpu_lock); + chunk = alloc_pcpu_chunk(); if (!chunk) - goto out_unlock; + goto fail_unlock_mutex; + + spin_lock_irq(&pcpu_lock); pcpu_chunk_relocate(chunk, -1); pcpu_chunk_addr_insert(chunk); - - off = pcpu_alloc_area(chunk, size, align); - if (off < 0) - goto out_unlock; + goto restart; area_found: + spin_unlock_irq(&pcpu_lock); + /* populate, map and clear the area */ if (pcpu_populate_chunk(chunk, off, size)) { + spin_lock_irq(&pcpu_lock); pcpu_free_area(chunk, off); - goto out_unlock; + goto fail_unlock; } - ptr = __addr_to_pcpu_ptr(chunk->vm->addr + off); -out_unlock: - mutex_unlock(&pcpu_mutex); - return ptr; + mutex_unlock(&pcpu_alloc_mutex); + + return __addr_to_pcpu_ptr(chunk->vm->addr + off); + +fail_unlock: + spin_unlock_irq(&pcpu_lock); +fail_unlock_mutex: + mutex_unlock(&pcpu_alloc_mutex); + return NULL; } /** @@ -825,6 +897,9 @@ out_unlock: * Allocate percpu area of @size bytes aligned at @align. Might * sleep. Might trigger writeouts. * + * CONTEXT: + * Does GFP_KERNEL allocation. + * * RETURNS: * Percpu pointer to the allocated area on success, NULL on failure. */ @@ -843,6 +918,9 @@ EXPORT_SYMBOL_GPL(__alloc_percpu); * percpu area if arch has set it up; otherwise, allocation is served * from the same dynamic area. Might sleep. Might trigger writeouts. * + * CONTEXT: + * Does GFP_KERNEL allocation. + * * RETURNS: * Percpu pointer to the allocated area on success, NULL on failure. */ @@ -856,6 +934,9 @@ void *__alloc_reserved_percpu(size_t size, size_t align) * @work: unused * * Reclaim all fully free chunks except for the first one. + * + * CONTEXT: + * workqueue context. */ static void pcpu_reclaim(struct work_struct *work) { @@ -863,7 +944,8 @@ static void pcpu_reclaim(struct work_struct *work) struct list_head *head = &pcpu_slot[pcpu_nr_slots - 1]; struct pcpu_chunk *chunk, *next; - mutex_lock(&pcpu_mutex); + mutex_lock(&pcpu_alloc_mutex); + spin_lock_irq(&pcpu_lock); list_for_each_entry_safe(chunk, next, head, list) { WARN_ON(chunk->immutable); @@ -876,7 +958,8 @@ static void pcpu_reclaim(struct work_struct *work) list_move(&chunk->list, &todo); } - mutex_unlock(&pcpu_mutex); + spin_unlock_irq(&pcpu_lock); + mutex_unlock(&pcpu_alloc_mutex); list_for_each_entry_safe(chunk, next, &todo, list) { pcpu_depopulate_chunk(chunk, 0, pcpu_unit_size, false); @@ -888,18 +971,22 @@ static void pcpu_reclaim(struct work_struct *work) * free_percpu - free percpu area * @ptr: pointer to area to free * - * Free percpu area @ptr. Might sleep. + * Free percpu area @ptr. + * + * CONTEXT: + * Can be called from atomic context. */ void free_percpu(void *ptr) { void *addr = __pcpu_ptr_to_addr(ptr); struct pcpu_chunk *chunk; + unsigned long flags; int off; if (!ptr) return; - mutex_lock(&pcpu_mutex); + spin_lock_irqsave(&pcpu_lock, flags); chunk = pcpu_chunk_addr_search(addr); off = addr - chunk->vm->addr; @@ -917,7 +1004,7 @@ void free_percpu(void *ptr) } } - mutex_unlock(&pcpu_mutex); + spin_unlock_irqrestore(&pcpu_lock, flags); } EXPORT_SYMBOL_GPL(free_percpu); |
