From: Paul Moore <paul@paul-moore.com>
To: "Christian Göttsche" <cgzones@googlemail.com>, selinux@vger.kernel.org
Cc: Stephen Smalley <stephen.smalley.work@gmail.com>,
Ondrej Mosnacek <omosnace@redhat.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3] selinux: optimize ebitmap_and()
Date: Wed, 27 Mar 2024 18:07:44 -0400 [thread overview]
Message-ID: <66718f36ae0e8dbad8bbf74038e9e0d6@paul-moore.com> (raw)
In-Reply-To: <20240315181204.647182-1-cgzones@googlemail.com>
On Mar 15, 2024 =?UTF-8?q?Christian=20G=C3=B6ttsche?= <cgzones@googlemail.com> wrote:
>
> Iterate on nodes instead of single bits to save node resolution for each
> single bit.
>
> Similar to userspace patch efcd00814879 ("libsepol: optimize
> ebitmap_and").
>
> Signed-off-by: Christian Göttsche <cgzones@googlemail.com>
> ---
> v3:
> apply format style
> v2:
> fix array size computation
> ---
> security/selinux/ss/ebitmap.c | 50 +++++++++++++++++++++++++++++------
> 1 file changed, 42 insertions(+), 8 deletions(-)
Some minor comments below, but do you have any performance measurements
for this change? I realize that ebitmap_and() isn't widely used, but
it would be nice to understand the performance difference, and if there
isn't much/any difference we might want to stick with the original code
as it is much simpler.
> diff --git a/security/selinux/ss/ebitmap.c b/security/selinux/ss/ebitmap.c
> index 67c1a73cd5ee..47cb90106118 100644
> --- a/security/selinux/ss/ebitmap.c
> +++ b/security/selinux/ss/ebitmap.c
> @@ -78,19 +78,53 @@ int ebitmap_cpy(struct ebitmap *dst, const struct ebitmap *src)
> int ebitmap_and(struct ebitmap *dst, const struct ebitmap *e1,
> const struct ebitmap *e2)
> {
> - struct ebitmap_node *n;
> - int bit, rc;
> + const struct ebitmap_node *n1, *n2;
> + struct ebitmap_node *new = NULL, **prev;
>
> ebitmap_init(dst);
>
> - ebitmap_for_each_positive_bit(e1, n, bit)
> - {
> - if (ebitmap_get_bit(e2, bit)) {
> - rc = ebitmap_set_bit(dst, bit, 1);
> - if (rc < 0)
> - return rc;
> + prev = &dst->node;
Later in this function you include parenthesis, that might be nice
here too:
prev = &(dst->node);
> + n1 = e1->node;
> + n2 = e2->node;
> + while (n1 && n2) {
> + if (n1->startbit == n2->startbit) {
> + unsigned long testmap[EBITMAP_UNIT_NUMS];
This is very bikeshed-y, but I much prefer "dstmaps" over "testmap".
> + unsigned int i;
> + bool match = false;
> +
> + for (i = 0; i < ARRAY_SIZE(testmap); i++) {
> + testmap[i] = n1->maps[i] & n2->maps[i];
> + if (testmap[i] != 0)
If I'm going to be nitpicky, I'd probably prefer 'if (!dstmaps[i])'.
> + match = true;
> + }
> +
> + if (match) {
> + new = kmem_cache_zalloc(ebitmap_node_cachep,
> + GFP_ATOMIC);
> + if (!new) {
> + ebitmap_destroy(dst);
> + return -ENOMEM;
> + }
> + new->startbit = n1->startbit;
> + memcpy(new->maps, testmap, EBITMAP_SIZE / 8);
Why not just use 'sizeof(dstmaps)'?
memcpy(new->maps, dstmaps, sizeof(dstmaps));
> + new->next = NULL;
You shouldn't need the line above since you're doing a _zalloc().
> + *prev = new;
> + prev = &(new->next);
> + }
> +
> + n1 = n1->next;
> + n2 = n2->next;
> + } else if (n1->startbit > n2->startbit) {
> + n2 = n2->next;
> + } else {
> + n1 = n1->next;
> }
> }
> +
> + if (new)
> + dst->highbit = new->startbit + EBITMAP_SIZE;
> +
> return 0;
> }
>
> --
> 2.43.0
--
paul-moore.com
prev parent reply other threads:[~2024-03-27 22:07 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-03-15 18:11 [PATCH v3] selinux: optimize ebitmap_and() Christian Göttsche
2024-03-27 22:07 ` Paul Moore [this message]
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