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Commit 6ee211ad authored by Li Zefan's avatar Li Zefan Committed by Tejun Heo
Browse files

cgroup: don't bother to resize pid array 



When we open cgroup.procs, we'll allocate an buffer and store all tasks'
tgid in it, and then duplicate entries will be stripped. If that results
in a much smaller pid list, we'll re-allocate a smaller buffer.

But we've already sucessfully allocated memory and reading the procs
file is a short period and the memory will be freed very soon, so why
bother to re-allocate memory.

Signed-off-by: default avatarLi Zefan <lizefan@huawei.com>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
parent d7eeac19

kernel/cgroup.c

+3 −34
Original line number Diff line number Diff line
@@ -3400,35 +3400,14 @@ static void pidlist_free(void *p) 
	else

		kfree(p);

}

static void *pidlist_resize(void *p, int newcount)

{

	void *newlist;

	/* note: if new alloc fails, old p will still be valid either way */

	if (is_vmalloc_addr(p)) {

		newlist = vmalloc(newcount * sizeof(pid_t));

		if (!newlist)

			return NULL;

		memcpy(newlist, p, newcount * sizeof(pid_t));

		vfree(p);

	} else {

		newlist = krealloc(p, newcount * sizeof(pid_t), GFP_KERNEL);

	}

	return newlist;

}



/*

 * pidlist_uniq - given a kmalloc()ed list, strip out all duplicate entries

 * If the new stripped list is sufficiently smaller and there's enough memory

 * to allocate a new buffer, will let go of the unneeded memory. Returns the

 * number of unique elements.

 * Returns the number of unique elements.

 */

/* is the size difference enough that we should re-allocate the array? */

#define PIDLIST_REALLOC_DIFFERENCE(old, new) ((old) - PAGE_SIZE >= (new))

static int pidlist_uniq(pid_t **p, int length)

static int pidlist_uniq(pid_t *list, int length)

{

	int src, dest = 1;

	pid_t *list = *p;

	pid_t *newlist;



	/*

	 * we presume the 0th element is unique, so i starts at 1. trivial
@@ -3449,16 +3428,6 @@ static int pidlist_uniq(pid_t **p, int length) 
		dest++;

	}

after:

	/*

	 * if the length difference is large enough, we want to allocate a

	 * smaller buffer to save memory. if this fails due to out of memory,

	 * we'll just stay with what we've got.

	 */

	if (PIDLIST_REALLOC_DIFFERENCE(length, dest)) {

		newlist = pidlist_resize(list, dest);

		if (newlist)

			*p = newlist;

	}

	return dest;

}
@@ -3554,7 +3523,7 @@ static int pidlist_array_load(struct cgroup *cgrp, enum cgroup_filetype type, 
	/* now sort & (if procs) strip out duplicates */

	sort(array, length, sizeof(pid_t), cmppid, NULL);

	if (type == CGROUP_FILE_PROCS)

		length = pidlist_uniq(&array, length);

		length = pidlist_uniq(array, length);

	l = cgroup_pidlist_find(cgrp, type);

	if (!l) {

		pidlist_free(array);