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bpf: Add a few bpf mem allocator functions 

This patch adds a few bpf mem allocator functions which will
be used in the bpf_local_storage in a later patch.

bpf_mem_cache_alloc_flags(..., gfp_t flags) is added. When the
flags == GFP_KERNEL, it will fallback to __alloc(..., GFP_KERNEL).
bpf_local_storage knows its running context is sleepable (GFP_KERNEL)
and provides a better guarantee on memory allocation.

bpf_local_storage has some uncommon cases that its selem
cannot be reused immediately. It handles its own
rcu_head and goes through a rcu_trace gp and then free it.
bpf_mem_cache_raw_free() is added for direct free purpose
without leaking the LLIST_NODE_SZ internal knowledge.
During free time, the 'struct bpf_mem_alloc *ma' is no longer
available. However, the caller should know if it is
percpu memory or not and it can call different raw_free functions.
bpf_local_storage does not support percpu value, so only
the non-percpu 'bpf_mem_cache_raw_free()' is added in
this patch.

Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Link: https://lore.kernel.org/r/20230322215246.1675516-2-martin.lau@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Martin KaFai Lau 2023-03-22 14:52:42 -07:00 committed by Alexei Starovoitov
parent e99360762a
commit e65a5c6edb
2 changed files with 52 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
include/linux/bpf_mem_alloc.h
View File

@ -31,5 +31,7 @@ void bpf_mem_free(struct bpf_mem_alloc *ma, void *ptr);
/* kmem_cache_alloc/free equivalent: */
void *bpf_mem_cache_alloc(struct bpf_mem_alloc *ma);
void bpf_mem_cache_free(struct bpf_mem_alloc *ma, void *ptr);
void bpf_mem_cache_raw_free(void *ptr);
void *bpf_mem_cache_alloc_flags(struct bpf_mem_alloc *ma, gfp_t flags);
#endif /* _BPF_MEM_ALLOC_H */

59
kernel/bpf/memalloc.c
View File

@ -121,15 +121,8 @@ static struct llist_node notrace *__llist_del_first(struct llist_head *head)
return entry;
}
static void *__alloc(struct bpf_mem_cache *c, int node)
static void *__alloc(struct bpf_mem_cache *c, int node, gfp_t flags)
{
/* Allocate, but don't deplete atomic reserves that typical
* GFP_ATOMIC would do. irq_work runs on this cpu and kmalloc
* will allocate from the current numa node which is what we
* want here.
*/
gfp_t flags = GFP_NOWAIT | __GFP_NOWARN | __GFP_ACCOUNT;
if (c->percpu_size) {
void **obj = kmalloc_node(c->percpu_size, flags, node);
void *pptr = __alloc_percpu_gfp(c->unit_size, 8, flags);
@ -185,7 +178,12 @@ static void alloc_bulk(struct bpf_mem_cache *c, int cnt, int node)
*/
obj = __llist_del_first(&c->free_by_rcu);
if (!obj) {
obj = __alloc(c, node);
/* Allocate, but don't deplete atomic reserves that typical
* GFP_ATOMIC would do. irq_work runs on this cpu and kmalloc
* will allocate from the current numa node which is what we
* want here.
*/
obj = __alloc(c, node, GFP_NOWAIT | __GFP_NOWARN | __GFP_ACCOUNT);
if (!obj)
break;
}
@ -676,3 +674,46 @@ void notrace bpf_mem_cache_free(struct bpf_mem_alloc *ma, void *ptr)
unit_free(this_cpu_ptr(ma->cache), ptr);
}
/* Directly does a kfree() without putting 'ptr' back to the free_llist
* for reuse and without waiting for a rcu_tasks_trace gp.
* The caller must first go through the rcu_tasks_trace gp for 'ptr'
* before calling bpf_mem_cache_raw_free().
* It could be used when the rcu_tasks_trace callback does not have
* a hold on the original bpf_mem_alloc object that allocated the
* 'ptr'. This should only be used in the uncommon code path.
* Otherwise, the bpf_mem_alloc's free_llist cannot be refilled
* and may affect performance.
*/
void bpf_mem_cache_raw_free(void *ptr)
{
if (!ptr)
return;
kfree(ptr - LLIST_NODE_SZ);
}
/* When flags == GFP_KERNEL, it signals that the caller will not cause
* deadlock when using kmalloc. bpf_mem_cache_alloc_flags() will use
* kmalloc if the free_llist is empty.
*/
void notrace *bpf_mem_cache_alloc_flags(struct bpf_mem_alloc *ma, gfp_t flags)
{
struct bpf_mem_cache *c;
void *ret;
c = this_cpu_ptr(ma->cache);
ret = unit_alloc(c);
if (!ret && flags == GFP_KERNEL) {
struct mem_cgroup *memcg, *old_memcg;
memcg = get_memcg(c);
old_memcg = set_active_memcg(memcg);
ret = __alloc(c, NUMA_NO_NODE, GFP_KERNEL | __GFP_NOWARN | __GFP_ACCOUNT);
set_active_memcg(old_memcg);
mem_cgroup_put(memcg);
}
return !ret ? NULL : ret + LLIST_NODE_SZ;
}