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Date: Wed, 16 Nov 2022 18:49:05 +0800
From: wuqiang <wuqiang.matt@...edance.com>
To: "Masami Hiramatsu (Google)" <mhiramat@...nel.org>
Cc: davem@...emloft.net, anil.s.keshavamurthy@...el.com,
naveen.n.rao@...ux.ibm.com, rostedt@...dmis.org,
peterz@...radead.org, akpm@...ux-foundation.org,
sander@...nheule.net, ebiggers@...gle.com,
dan.j.williams@...el.com, jpoimboe@...nel.org,
linux-kernel@...r.kernel.org, lkp@...el.com, mattwu@....com
Subject: Re: [PATCH v6 3/4] kprobes: kretprobe scalability improvement with
objpool
On 2022/11/14 23:56, Masami Hiramatsu (Google) wrote:
> Hi Wuqiang,
>
> On Tue, 8 Nov 2022 15:14:42 +0800
> wuqiang <wuqiang.matt@...edance.com> wrote:
>
>> kretprobe is using freelist to manage return-instances, but freelist,
>> as LIFO queue based on singly linked list, scales badly and reduces
>> the overall throughput of kretprobed routines, especially for high
>> contention scenarios.
>>
>> Here's a typical throughput test of sys_flock (counts in 10 seconds,
>> measured with perf stat -a -I 10000 -e syscalls:sys_enter_flock):
>>
>> OS: Debian 10 X86_64, Linux 6.1rc2
>> HW: XEON 8336C x 2, 64 cores/128 threads, DDR4 3200MT/s
>>
>> 1X 2X 4X 6X 8X 12X 16X
>> 34762430 36546920 17949900 13101899 12569595 12646601 14729195
>> 24X 32X 48X 64X 72X 96X 128X
>> 19263546 10102064 8985418 11936495 11493980 7127789 9330985
>>
>> This patch introduces objpool to kretprobe and rethook, with orginal
>> freelist replaced and brings near-linear scalability to kretprobed
>> routines. Tests of kretprobe throughput show the biggest ratio as
>> 333.9x of the original freelist. Here's the comparison:
>>
>> 1X 2X 4X 8X 16X
>> freelist: 34762430 36546920 17949900 12569595 14729195
>> objpool: 35627544 72182095 144068494 287564688 576903916
>> 32X 48X 64X 96X 128X
>> freelist: 10102064 8985418 11936495 7127789 9330985
>> objpool: 1158876372 1737828164 2324371724 2380310472 2463182819
>>
>> Tests on 96-core ARM64 system output similarly, but with the biggest
>> ratio up to 642.2x:
>>
>> OS: Debian 10 AARCH64, Linux 6.1rc2
>> HW: Kunpeng-920 96 cores/2 sockets/4 NUMA nodes, DDR4 2933 MT/s
>>
>> 1X 2X 4X 8X 16X
>> freelist: 17498299 10887037 10224710 8499132 6421751
>> objpool: 18715726 35549845 71615884 144258971 283707220
>> 24X 32X 48X 64X 96X
>> freelist: 5339868 4819116 3593919 3121575 2687167
>> objpool: 419830913 571609748 877456139 1143316315 1725668029
>>
>> Signed-off-by: wuqiang <wuqiang.matt@...edance.com>
>> ---
>> include/linux/kprobes.h | 9 ++--
>> include/linux/rethook.h | 15 +++----
>> kernel/kprobes.c | 95 +++++++++++++++++++----------------------
>> kernel/trace/fprobe.c | 17 ++------
>> kernel/trace/rethook.c | 80 +++++++++++++++++-----------------
>> 5 files changed, 95 insertions(+), 121 deletions(-)
>>
>> diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
>> index a0b92be98984..f13f01e600c2 100644
>> --- a/include/linux/kprobes.h
>> +++ b/include/linux/kprobes.h
>> @@ -27,7 +27,7 @@
>> #include <linux/mutex.h>
>> #include <linux/ftrace.h>
>> #include <linux/refcount.h>
>> -#include <linux/freelist.h>
>> +#include <linux/objpool.h>
>> #include <linux/rethook.h>
>> #include <asm/kprobes.h>
>>
>> @@ -141,6 +141,7 @@ static inline bool kprobe_ftrace(struct kprobe *p)
>> */
>> struct kretprobe_holder {
>> struct kretprobe *rp;
>> + struct objpool_head oh;
>
> Could you rename it to `pool` as rethook does?
Sure. Will udpate in next version.
>> refcount_t ref;
>> };
>>
>> @@ -154,7 +155,6 @@ struct kretprobe {
>> #ifdef CONFIG_KRETPROBE_ON_RETHOOK
>> struct rethook *rh;
>> #else
>> - struct freelist_head freelist;
>
> OK, this is natural to move the head to kretprobe_holder, because
> objpool must call its fini() function when all objects are freed.
>
>> struct kretprobe_holder *rph;
>> #endif
>> };
>> @@ -165,10 +165,7 @@ struct kretprobe_instance {
>> #ifdef CONFIG_KRETPROBE_ON_RETHOOK
>> struct rethook_node node;
>> #else
>> - union {
>> - struct freelist_node freelist;
>> - struct rcu_head rcu;
>> - };
>> + struct rcu_head rcu;
>> struct llist_node llist;
>> struct kretprobe_holder *rph;
>> kprobe_opcode_t *ret_addr;
>> diff --git a/include/linux/rethook.h b/include/linux/rethook.h
>> index c8ac1e5afcd1..278ec65e71fe 100644
>> --- a/include/linux/rethook.h
>> +++ b/include/linux/rethook.h
>> @@ -6,7 +6,7 @@
>> #define _LINUX_RETHOOK_H
>>
>> #include <linux/compiler.h>
>> -#include <linux/freelist.h>
>> +#include <linux/objpool.h>
>> #include <linux/kallsyms.h>
>> #include <linux/llist.h>
>> #include <linux/rcupdate.h>
>> @@ -30,14 +30,14 @@ typedef void (*rethook_handler_t) (struct rethook_node *, void *, struct pt_regs
>> struct rethook {
>> void *data;
>> rethook_handler_t handler;
>> - struct freelist_head pool;
>> + struct objpool_head pool;
>
> On the other hand, the rethook already consolidated that "holder"
> feature to itself, so you don't need to move, just replace the
> freelist_head with objpool_head. LGTM.
>
>> refcount_t ref;
>> struct rcu_head rcu;
>> };
>>
>> /**
>> * struct rethook_node - The rethook shadow-stack entry node.
>> - * @freelist: The freelist, linked to struct rethook::pool.
>> + * @nod: The objpool node, linked to struct rethook::pool.
>
> I don't see @nod in rethook_node. maybe a typo?
My mistake. Forget to remove it when migrating to ring-array based objpool
from the freelist version.
>> * @rcu: The rcu_head for deferred freeing.
>> * @llist: The llist, linked to a struct task_struct::rethooks.
>> * @rethook: The pointer to the struct rethook.
>> @@ -48,19 +48,15 @@ struct rethook {
>> * on each entry of the shadow stack.
>> */
>> struct rethook_node {
>> - union {
>> - struct freelist_node freelist;
>> - struct rcu_head rcu;
>> - };
>> + struct rcu_head rcu;
>> struct llist_node llist;
>> struct rethook *rethook;
>> unsigned long ret_addr;
>> unsigned long frame;
>> };
>>
>> -struct rethook *rethook_alloc(void *data, rethook_handler_t handler);
>> +struct rethook *rethook_alloc(void *data, rethook_handler_t handler, gfp_t gfp, int size, int max);
>> void rethook_free(struct rethook *rh);
>> -void rethook_add_node(struct rethook *rh, struct rethook_node *node);
>> struct rethook_node *rethook_try_get(struct rethook *rh);
>> void rethook_recycle(struct rethook_node *node);
>> void rethook_hook(struct rethook_node *node, struct pt_regs *regs, bool mcount);
>> @@ -97,4 +93,3 @@ void rethook_flush_task(struct task_struct *tk);
>> #endif
>>
>> #endif
>> -
>> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
>> index cd9f5a66a690..a8b202f87e2d 100644
>> --- a/kernel/kprobes.c
>> +++ b/kernel/kprobes.c
>> @@ -1865,10 +1865,12 @@ static struct notifier_block kprobe_exceptions_nb = {
>> static void free_rp_inst_rcu(struct rcu_head *head)
>> {
>> struct kretprobe_instance *ri = container_of(head, struct kretprobe_instance, rcu);
>> + struct kretprobe_holder *rph = ri->rph;
>>
>> - if (refcount_dec_and_test(&ri->rph->ref))
>> - kfree(ri->rph);
>> - kfree(ri);
>> + if (refcount_dec_and_test(&rph->ref)) {
>> + objpool_fini(&rph->oh);
>> + kfree(rph);
>> + }
>> }
>> NOKPROBE_SYMBOL(free_rp_inst_rcu);
>>
>> @@ -1877,7 +1879,7 @@ static void recycle_rp_inst(struct kretprobe_instance *ri)
>> struct kretprobe *rp = get_kretprobe(ri);
>>
>> if (likely(rp))
>> - freelist_add(&ri->freelist, &rp->freelist);
>> + objpool_push(ri, &rp->rph->oh);
>> else
>> call_rcu(&ri->rcu, free_rp_inst_rcu);
>> }
>> @@ -1914,23 +1916,19 @@ NOKPROBE_SYMBOL(kprobe_flush_task);
>>
>> static inline void free_rp_inst(struct kretprobe *rp)
>> {
>> - struct kretprobe_instance *ri;
>> - struct freelist_node *node;
>> - int count = 0;
>> -
>> - node = rp->freelist.head;
>> - while (node) {
>> - ri = container_of(node, struct kretprobe_instance, freelist);
>> - node = node->next;
>> -
>> - kfree(ri);
>> - count++;
>> - }
>> + struct kretprobe_holder *rph = rp->rph;
>> + void *nod;
>>
>> - if (refcount_sub_and_test(count, &rp->rph->ref)) {
>> - kfree(rp->rph);
>> - rp->rph = NULL;
>> - }
>> + rp->rph = NULL;
>> + do {
>> + nod = objpool_pop(&rph->oh);
>> + /* deref anyway since we've one extra ref grabbed */
>> + if (refcount_dec_and_test(&rph->ref)) {
>> + objpool_fini(&rph->oh);
>> + kfree(rph);
>> + break;
>> + }
>> + } while (nod);
>> }
>>
>> /* This assumes the 'tsk' is the current task or the is not running. */
>> @@ -2072,19 +2070,17 @@ NOKPROBE_SYMBOL(__kretprobe_trampoline_handler)
>> static int pre_handler_kretprobe(struct kprobe *p, struct pt_regs *regs)
>> {
>> struct kretprobe *rp = container_of(p, struct kretprobe, kp);
>> + struct kretprobe_holder *rph = rp->rph;
>> struct kretprobe_instance *ri;
>> - struct freelist_node *fn;
>>
>> - fn = freelist_try_get(&rp->freelist);
>> - if (!fn) {
>> + ri = objpool_pop(&rph->oh);
>> + if (!ri) {
>> rp->nmissed++;
>> return 0;
>> }
>>
>> - ri = container_of(fn, struct kretprobe_instance, freelist);
>> -
>> if (rp->entry_handler && rp->entry_handler(ri, regs)) {
>> - freelist_add(&ri->freelist, &rp->freelist);
>> + objpool_push(ri, &rph->oh);
>> return 0;
>> }
>>
>> @@ -2174,10 +2170,19 @@ int kprobe_on_func_entry(kprobe_opcode_t *addr, const char *sym, unsigned long o
>> return 0;
>> }
>>
>> +#ifndef CONFIG_KRETPROBE_ON_RETHOOK
>> +static int kretprobe_init_inst(void *context, void *nod)
>> +{
>> + struct kretprobe_instance *ri = nod;
>> +
>> + ri->rph = context;
>> + return 0;
>> +}
>> +#endif
>> +
>> int register_kretprobe(struct kretprobe *rp)
>> {
>> int ret;
>> - struct kretprobe_instance *inst;
>> int i;
>> void *addr;
>>
>> @@ -2215,20 +2220,12 @@ int register_kretprobe(struct kretprobe *rp)
>> #endif
>> }
>> #ifdef CONFIG_KRETPROBE_ON_RETHOOK
>> - rp->rh = rethook_alloc((void *)rp, kretprobe_rethook_handler);
>> + rp->rh = rethook_alloc((void *)rp, kretprobe_rethook_handler, GFP_KERNEL,
>> + sizeof(struct kretprobe_instance) + rp->data_size,
>> + rp->maxactive);
>> if (!rp->rh)
>> return -ENOMEM;
>>
>> - for (i = 0; i < rp->maxactive; i++) {
>> - inst = kzalloc(sizeof(struct kretprobe_instance) +
>> - rp->data_size, GFP_KERNEL);
>> - if (inst == NULL) {
>> - rethook_free(rp->rh);
>> - rp->rh = NULL;
>> - return -ENOMEM;
>> - }
>> - rethook_add_node(rp->rh, &inst->node);
>> - }
>> rp->nmissed = 0;
>> /* Establish function entry probe point */
>> ret = register_kprobe(&rp->kp);
>> @@ -2237,25 +2234,19 @@ int register_kretprobe(struct kretprobe *rp)
>> rp->rh = NULL;
>> }
>> #else /* !CONFIG_KRETPROBE_ON_RETHOOK */
>> - rp->freelist.head = NULL;
>> rp->rph = kzalloc(sizeof(struct kretprobe_holder), GFP_KERNEL);
>> if (!rp->rph)
>> return -ENOMEM;
>>
>> - rp->rph->rp = rp;
>> - for (i = 0; i < rp->maxactive; i++) {
>> - inst = kzalloc(sizeof(struct kretprobe_instance) +
>> - rp->data_size, GFP_KERNEL);
>> - if (inst == NULL) {
>> - refcount_set(&rp->rph->ref, i);
>> - free_rp_inst(rp);
>> - return -ENOMEM;
>> - }
>> - inst->rph = rp->rph;
>> - freelist_add(&inst->freelist, &rp->freelist);
>> + if (objpool_init(&rp->rph->oh, rp->maxactive, rp->maxactive,
>> + rp->data_size + sizeof(struct kretprobe_instance),
>> + GFP_KERNEL, rp->rph, kretprobe_init_inst, NULL)) {
>> + kfree(rp->rph);
>> + rp->rph = NULL;
>> + return -ENOMEM;
>> }
>> - refcount_set(&rp->rph->ref, i);
>> -
>> + refcount_set(&rp->rph->ref, rp->maxactive + 1);
>> + rp->rph->rp = rp;
>> rp->nmissed = 0;
>> /* Establish function entry probe point */
>> ret = register_kprobe(&rp->kp);
>> diff --git a/kernel/trace/fprobe.c b/kernel/trace/fprobe.c
>> index e8143e368074..9a002bfbd216 100644
>> --- a/kernel/trace/fprobe.c
>> +++ b/kernel/trace/fprobe.c
>> @@ -125,7 +125,7 @@ static void fprobe_init(struct fprobe *fp)
>>
>> static int fprobe_init_rethook(struct fprobe *fp, int num)
>> {
>> - int i, size;
>> + int size;
>>
>> if (num < 0)
>> return -EINVAL;
>> @@ -140,20 +140,11 @@ static int fprobe_init_rethook(struct fprobe *fp, int num)
>> if (size < 0)
>> return -E2BIG;
>>
>> - fp->rethook = rethook_alloc((void *)fp, fprobe_exit_handler);
>> + fp->rethook = rethook_alloc((void *)fp, fprobe_exit_handler, GFP_KERNEL,
>> + sizeof(struct fprobe_rethook_node), size);
>> if (!fp->rethook)
>> return -ENOMEM;
>> - for (i = 0; i < size; i++) {
>> - struct fprobe_rethook_node *node;
>> -
>> - node = kzalloc(sizeof(*node), GFP_KERNEL);
>> - if (!node) {
>> - rethook_free(fp->rethook);
>> - fp->rethook = NULL;
>> - return -ENOMEM;
>> - }
>> - rethook_add_node(fp->rethook, &node->node);
>> - }
>> +
>> return 0;
>> }
>>
>> diff --git a/kernel/trace/rethook.c b/kernel/trace/rethook.c
>> index c69d82273ce7..01df98db2fbe 100644
>> --- a/kernel/trace/rethook.c
>> +++ b/kernel/trace/rethook.c
>> @@ -36,21 +36,17 @@ void rethook_flush_task(struct task_struct *tk)
>> static void rethook_free_rcu(struct rcu_head *head)
>> {
>> struct rethook *rh = container_of(head, struct rethook, rcu);
>> - struct rethook_node *rhn;
>> - struct freelist_node *node;
>> - int count = 1;
>> + struct rethook_node *nod;
>>
>> - node = rh->pool.head;
>> - while (node) {
>> - rhn = container_of(node, struct rethook_node, freelist);
>> - node = node->next;
>> - kfree(rhn);
>> - count++;
>> - }
>> -
>> - /* The rh->ref is the number of pooled node + 1 */
>> - if (refcount_sub_and_test(count, &rh->ref))
>> - kfree(rh);
>> + do {
>> + nod = objpool_pop(&rh->pool);
>> + /* deref anyway since we've one extra ref grabbed */
>> + if (refcount_dec_and_test(&rh->ref)) {
>> + objpool_fini(&rh->pool);
>> + kfree(rh);
>> + break;
>> + }
>> + } while (nod);
>> }
>>
>> /**
>> @@ -70,16 +66,28 @@ void rethook_free(struct rethook *rh)
>> call_rcu(&rh->rcu, rethook_free_rcu);
>> }
>>
>> +static int rethook_init_node(void *context, void *nod)
>> +{
>> + struct rethook_node *node = nod;
>> +
>> + node->rethook = context;
>> + return 0;
>> +}
>> +
>> /**
>> * rethook_alloc() - Allocate struct rethook.
>> * @data: a data to pass the @handler when hooking the return.
>> * @handler: the return hook callback function.
>> + * @gfp: default gfp for objpool allocation
>> + * @size: rethook node size
>
> @size should be @data_size, which is the size of additional data bytes
> of rethook_node.
Got it.
>> + * @max: number of rethook nodes to be preallocated
>> *
>> * Allocate and initialize a new rethook with @data and @handler.
>> * Return NULL if memory allocation fails or @handler is NULL.
>> * Note that @handler == NULL means this rethook is going to be freed.
>> */
>> -struct rethook *rethook_alloc(void *data, rethook_handler_t handler)
>> +struct rethook *rethook_alloc(void *data, rethook_handler_t handler, gfp_t gfp,
>> + int size, int max)
>
> This doesn't need @gfp. Just use GFP_KERNEL from rethook layer.
Ok.
>> {
>> struct rethook *rh = kzalloc(sizeof(struct rethook), GFP_KERNEL);
>
> And here,
>
> if (data_size < 0 || max < 0)
> return -EINVAL;
>
I will update it in next version.
>>
>> @@ -88,34 +96,26 @@ struct rethook *rethook_alloc(void *data, rethook_handler_t handler)
>>
>> rh->data = data;
>> rh->handler = handler;
>> - rh->pool.head = NULL;
>> - refcount_set(&rh->ref, 1);
>>
>> + /* initialize the objpool for rethook nodes */
>> + if (objpool_init(&rh->pool, max, max, size, gfp, rh, rethook_init_node,
>> + NULL)) {
>> + kfree(rh);
>> + return NULL;
>> + }
>> + refcount_set(&rh->ref, max + 1);
>> return rh;
>> }
>>
>> -/**
>> - * rethook_add_node() - Add a new node to the rethook.
>> - * @rh: the struct rethook.
>> - * @node: the struct rethook_node to be added.
>> - *
>> - * Add @node to @rh. User must allocate @node (as a part of user's
>> - * data structure.) The @node fields are initialized in this function.
>> - */
>> -void rethook_add_node(struct rethook *rh, struct rethook_node *node)
>> -{
>> - node->rethook = rh;
>> - freelist_add(&node->freelist, &rh->pool);
>> - refcount_inc(&rh->ref);
>> -}
>> -
>> static void free_rethook_node_rcu(struct rcu_head *head)
>> {
>> struct rethook_node *node = container_of(head, struct rethook_node, rcu);
>> + struct rethook *rh = node->rethook;
>>
>> - if (refcount_dec_and_test(&node->rethook->ref))
>> - kfree(node->rethook);
>> - kfree(node);
>> + if (refcount_dec_and_test(&rh->ref)) {
>> + objpool_fini(&rh->pool);
>> + kfree(rh);
>> + }
>> }
>>
>> /**
>> @@ -130,7 +130,7 @@ void rethook_recycle(struct rethook_node *node)
>> lockdep_assert_preemption_disabled();
>>
>> if (likely(READ_ONCE(node->rethook->handler)))
>> - freelist_add(&node->freelist, &node->rethook->pool);
>> + objpool_push(node, &node->rethook->pool);
>> else
>> call_rcu(&node->rcu, free_rethook_node_rcu);
>> }
>> @@ -146,7 +146,7 @@ NOKPROBE_SYMBOL(rethook_recycle);
>> struct rethook_node *rethook_try_get(struct rethook *rh)
>> {
>> rethook_handler_t handler = READ_ONCE(rh->handler);
>> - struct freelist_node *fn;
>> + struct rethook_node *nod;
>>
>> lockdep_assert_preemption_disabled();
>>
>> @@ -163,11 +163,11 @@ struct rethook_node *rethook_try_get(struct rethook *rh)
>> if (unlikely(!rcu_is_watching()))
>> return NULL;
>>
>> - fn = freelist_try_get(&rh->pool);
>> - if (!fn)
>> + nod = (struct rethook_node *)objpool_pop(&rh->pool);
>> + if (!nod)
>> return NULL;
>>
>> - return container_of(fn, struct rethook_node, freelist);
>> + return nod;
>
> You can just write this part as
>
> return (struct rethook_node *)objpool_pop(&rh->pool);
Yes, sure.
> Thank you,
>
Best regards,
>> }
>> NOKPROBE_SYMBOL(rethook_try_get);
>>
>> --
>> 2.34.1
>>
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