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smb: client: fix compression heuristic functions

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Change is_compressible() return type to bool, use WARN_ON_ONCE(1) for
internal errors and return false for those.

Renames:
check_repeated_data -> has_repeated_data
check_ascii_bytes -> is_mostly_ascii (also refactor into a single loop)
calc_shannon_entropy -> has_low_entropy

Also wraps "wreq->Length" in le32_to_cpu() in should_compress() (caught
by sparse).

Signed-off-by: Enzo Matsumiya <ematsumiya@suse.de>
Suggested-by: Dan Carpenter <dan.carpenter@linaro.org>
Signed-off-by: Steve French <stfrench@microsoft.com>
This commit is contained in:
Enzo Matsumiya 2024-09-16 13:30:49 -03:00 committed by Steve French
parent 37408843f2
commit 5ac1f99fdd
1 changed files with 56 additions and 51 deletions
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107
fs/smb/client/compress.c
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@ -45,7 +45,7 @@ struct bucket {
};
/**
* calc_shannon_entropy() - Compute Shannon entropy of the sampled data.
* has_low_entropy() - Compute Shannon entropy of the sampled data.
* @bkt: Bytes counts of the sample.
* @slen: Size of the sample.
*
@ -60,7 +60,7 @@ struct bucket {
* Also Shannon entropy is the last computed heuristic; if we got this far and ended up
* with uncertainty, just stay on the safe side and call it uncompressible.
*/
static bool calc_shannon_entropy(struct bucket *bkt, size_t slen)
static bool has_low_entropy(struct bucket *bkt, size_t slen)
{
const size_t threshold = 65, max_entropy = 8 * ilog2(16);
size_t i, p, p2, len, sum = 0;
@ -79,17 +79,21 @@ static bool calc_shannon_entropy(struct bucket *bkt, size_t slen)
return ((sum * 100 / max_entropy) <= threshold);
}
#define BYTE_DIST_BAD 0
#define BYTE_DIST_GOOD 1
#define BYTE_DIST_MAYBE 2
/**
* calc_byte_distribution() - Compute byte distribution on the sampled data.
* @bkt: Byte counts of the sample.
* @slen: Size of the sample.
*
* Return:
* 1: High probability (normal (Gaussian) distribution) of the data being compressible.
* 0: A "hard no" for compression -- either a computed uniform distribution of the bytes (e.g.
* random or encrypted data), or calc_shannon_entropy() returned false (see above).
* 2: When computed byte distribution resulted in "low > n < high" grounds.
* calc_shannon_entropy() should be used for a final decision.
* BYTE_DIST_BAD: A "hard no" for compression -- a computed uniform distribution of
* the bytes (e.g. random or encrypted data).
* BYTE_DIST_GOOD: High probability (normal (Gaussian) distribution) of the data being
* compressible.
* BYTE_DIST_MAYBE: When computed byte distribution resulted in "low > n < high"
* grounds. has_low_entropy() should be used for a final decision.
*/
static int calc_byte_distribution(struct bucket *bkt, size_t slen)
{
@ -101,7 +105,7 @@ static int calc_byte_distribution(struct bucket *bkt, size_t slen)
sum += bkt[i].count;
if (sum > threshold)
return i;
return BYTE_DIST_BAD;
for (; i < high && bkt[i].count > 0; i++) {
sum += bkt[i].count;
@ -110,36 +114,29 @@ static int calc_byte_distribution(struct bucket *bkt, size_t slen)
}
if (i <= low)
return 1;
return BYTE_DIST_GOOD;
if (i >= high)
return 0;
return BYTE_DIST_BAD;
return 2;
return BYTE_DIST_MAYBE;
}
static bool check_ascii_bytes(const struct bucket *bkt)
static bool is_mostly_ascii(const struct bucket *bkt)
{
const size_t threshold = 64;
size_t count = 0;
int i;
for (i = 0; i < threshold; i++)
for (i = 0; i < 256; i++)
if (bkt[i].count > 0)
count++;
/* Too many non-ASCII (0-63) bytes. */
if (++count > 64)
return false;
for (; i < 256; i++) {
if (bkt[i].count > 0) {
count++;
if (count > threshold)
break;
}
}
return (count < threshold);
return true;
}
static bool check_repeated_data(const u8 *sample, size_t len)
static bool has_repeated_data(const u8 *sample, size_t len)
{
size_t s = len / 2;
@ -222,71 +219,79 @@ static int collect_sample(const struct iov_iter *iter, ssize_t max, u8 *sample)
* is_compressible() - Determines if a chunk of data is compressible.
* @data: Iterator containing uncompressed data.
*
* Return:
* 0: @data is not compressible
* 1: @data is compressible
* -ENOMEM: failed to allocate memory for sample buffer
* Return: true if @data is compressible, false otherwise.
*
* Tests shows that this function is quite reliable in predicting data compressibility,
* matching close to 1:1 with the behaviour of LZ77 compression success and failures.
*/
static int is_compressible(const struct iov_iter *data)
static bool is_compressible(const struct iov_iter *data)
{
const size_t read_size = SZ_2K, bkt_size = 256, max = SZ_4M;
struct bucket *bkt = NULL;
int i = 0, ret = 0;
size_t len;
u8 *sample;
bool ret = false;
int i;
/* Preventive double check -- already checked in should_compress(). */
len = iov_iter_count(data);
if (len < read_size)
return 0;
if (unlikely(len < read_size))
return ret;
if (len - read_size > max)
len = max;
sample = kvzalloc(len, GFP_KERNEL);
if (!sample)
return -ENOMEM;
if (!sample) {
WARN_ON_ONCE(1);
return ret;
}
/* Sample 2K bytes per page of the uncompressed data. */
ret = collect_sample(data, len, sample);
if (ret < 0)
i = collect_sample(data, len, sample);
if (i <= 0) {
WARN_ON_ONCE(1);
goto out;
}
len = ret;
ret = 1;
len = i;
ret = true;
if (check_repeated_data(sample, len))
if (has_repeated_data(sample, len))
goto out;
bkt = kcalloc(bkt_size, sizeof(*bkt), GFP_KERNEL);
if (!bkt) {
kvfree(sample);
return -ENOMEM;
WARN_ON_ONCE(1);
ret = false;
goto out;
}
for (i = 0; i < len; i++)
bkt[sample[i]].count++;
if (check_ascii_bytes(bkt))
if (is_mostly_ascii(bkt))
goto out;
/* Sort in descending order */
sort(bkt, bkt_size, sizeof(*bkt), cmp_bkt, NULL);
ret = calc_byte_distribution(bkt, len);
if (ret != 2)
goto out;
i = calc_byte_distribution(bkt, len);
if (i != BYTE_DIST_MAYBE) {
ret = !!i;
ret = calc_shannon_entropy(bkt, len);
goto out;
}
ret = has_low_entropy(bkt, len);
out:
kvfree(sample);
kfree(bkt);
WARN(ret < 0, "%s: ret=%d\n", __func__, ret);
return !!ret;
return ret;
}
bool should_compress(const struct cifs_tcon *tcon, const struct smb_rqst *rq)
@ -305,7 +310,7 @@ bool should_compress(const struct cifs_tcon *tcon, const struct smb_rqst *rq)
if (shdr->Command == SMB2_WRITE) {
const struct smb2_write_req *wreq = rq->rq_iov->iov_base;
if (wreq->Length < SMB_COMPRESS_MIN_LEN)
if (le32_to_cpu(wreq->Length) < SMB_COMPRESS_MIN_LEN)
return false;
return is_compressible(&rq->rq_iter);