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erm
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Move struct task cache to file scope. 

Making it a thread_local variable that can be used by any function means
we can set it from recurse_into_parents with ease, increasing the
likelihood it's set when allocating a new struct.

We also add a debugging print to the malloc branch in task allocation;
this allows us to compare how many allocations use p_old and how many
don't. Again with the linux kernel tree, ~50% of allocations now use
p_old.
This commit is contained in:
Érico Nogueira 2022-06-12 21:59:45 -03:00
parent a626ae594d
commit fe0c1705b2
1 changed files with 13 additions and 6 deletions
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19
remove.c
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@ -8,6 +8,7 @@
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <threads.h>
#include <unistd.h>
#include "erm.h"
@ -41,6 +42,9 @@ static pthread_cond_t fd_cond = PTHREAD_COND_INITIALIZER;
static unsigned nproc;
/* p_old is a struct task cache; this means each thread can leak one struct task in total */
static thread_local struct task *p_old = NULL;
static inline void queue_print(struct queue *q)
{
#ifdef DEBUGP
@ -96,8 +100,7 @@ static inline void queue_remove(struct queue *q, struct task *t)
static inline void recurse_into_parents(struct task *t)
{
struct task *recurse = t;
void *free_list = NULL;
struct task *recurse = t, *free_list = NULL;
while ((recurse = recurse->parent)) {
free(free_list); free_list = NULL;
@ -113,8 +116,10 @@ static inline void recurse_into_parents(struct task *t)
printf("rec rmdir succeeded '%s'\n", recurse->path);
}
free(recurse->path);
/* can't free now because the while condition uses it */
free_list = recurse;
if (p_old) free_list = recurse;
else p_old = recurse;
} else {
/* if we haven't removed this directory yet,
* there's no reason to recurse further */
@ -128,8 +133,7 @@ static inline void recurse_into_parents(struct task *t)
static void *process_queue_item(void *arg)
{
struct queue *q = arg;
/* p_old is a struct task cache; this means each thread can leak one struct task in total */
struct task t, *p_old = NULL;
struct task t;
while (1) {
queue_remove(q, &t);
@ -180,6 +184,7 @@ fast_path_dir:
puts("used p_old");
} else {
p = malloc(sizeof *p);
puts("didn't use p_old");
}
*p = t;
/* access happens only after mutex lock and release */
@ -208,7 +213,9 @@ fast_path_dir:
unsigned rc = atomic_fetch_and_explicit(&p->removed_count, ~ACQUIRED, memory_order_release);
if (rc == (n|ACQUIRED)) {
/* this branch is taken when other threads have already removed all of p's children */
p_old = p;
if (p_old) free(p);
else p_old = p;
if (rmdir(t.path)) {
fprintf(stderr, "atomic rmdir failed '%s': %m\n", t.path);
} else {