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fiemap: use hint index in get_extent to avoid O(n*m) extent lookups #399

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fiemap: use hint index in get_extent to avoid O(n*m) extent lookups #399

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8 changes: 7 additions & 1 deletion fiemap.c
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Original file line number Diff line number Diff line change
Expand Up @@ -48,8 +48,14 @@ struct fiemap_extent *get_extent(struct fiemap *fiemap, size_t loff,
{
struct fiemap_extent *extent;
size_t ext_end_off;
unsigned int start = 0;

for (unsigned int i = 0; i < fiemap->fm_mapped_extents; i++) {
/* Use hint if it doesn't point past the target offset */
if (index && *index < fiemap->fm_mapped_extents &&
fiemap->fm_extents[*index].fe_logical <= loff)
start = *index;

for (unsigned int i = start; i < fiemap->fm_mapped_extents; i++) {
extent = &fiemap->fm_extents[i];
ext_end_off = extent->fe_logical + extent->fe_length - 1;
if (ext_end_off < loff)
Expand Down
5 changes: 3 additions & 2 deletions fiemap.h
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Original file line number Diff line number Diff line change
Expand Up @@ -8,8 +8,9 @@
/*
* Given a filled fiemap structure, extract the struct fiemap_extent
* which covers the loff offset.
* If index is not NULL, then it will be filled with the extent's index.
* If no extent is found, returns NULL and index is garbage.
* If index is not NULL, it is used as a hint to start the search and
* updated with the found extent's index.
* If no extent is found, returns NULL and index is unchanged.
* The returned value must not be used after fiemap is freed, and must not
* be freed directly either.
*/
Expand Down
17 changes: 10 additions & 7 deletions file_scan.c
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Expand Up @@ -117,6 +117,7 @@ struct scan_ctxt {
struct fiemap *fiemap;
struct running_checksum *file_csum;
struct running_checksum *extent_csum;
unsigned int extent_hint; /* cached index for get_extent lookups */
};

/*
Expand Down Expand Up @@ -776,12 +777,13 @@ static int add_block_hash(struct hashes *hashes,
/*
* Check if the area should be scanned.
*/
static bool is_area_ignored(struct fiemap *fiemap, size_t start, size_t len)
static bool is_area_ignored(struct fiemap *fiemap, size_t start, size_t len,
unsigned int *extent_hint)
{
size_t end = start + len;
struct fiemap_extent *current_extent;
while (start < end) {
current_extent = get_extent(fiemap, start, NULL);
current_extent = get_extent(fiemap, start, extent_hint);

/* File changed since we fiemap */
if (!current_extent)
Expand All @@ -800,9 +802,10 @@ static bool is_area_ignored(struct fiemap *fiemap, size_t start, size_t len)
/*
* Check if the block starting at off should be ignored.
*/
static inline bool is_block_ignored(struct fiemap *fiemap, size_t off)
static inline bool is_block_ignored(struct fiemap *fiemap, size_t off,
unsigned int *extent_hint)
{
return is_area_ignored(fiemap, off, blocksize);
return is_area_ignored(fiemap, off, blocksize, extent_hint);
}

static int process_block(char *buf, unsigned int bsize,
Expand Down Expand Up @@ -830,7 +833,7 @@ static ssize_t process_blocks(struct scan_ctxt *ctxt, struct buffer *buffer,
return buffer->dl_len;

for (unsigned int i = 0; i < nb_blocks; i++) {
if (!is_block_ignored(ctxt->fiemap, curr_file_off) &&
if (!is_block_ignored(ctxt->fiemap, curr_file_off, &ctxt->extent_hint) &&
!(options.skip_zeroes &&
is_block_zeroed(buffer->buf + buffer->dl_offset))) {
ret = process_block(buffer->buf + i * blocksize,
Expand Down Expand Up @@ -885,7 +888,7 @@ static int process_extents(struct scan_ctxt *ctxt, struct buffer *buffer,
size_t to_add;

while (file_off < ctxt->off + bytes) {
extent = get_extent(ctxt->fiemap, file_off, NULL);
extent = get_extent(ctxt->fiemap, file_off, &ctxt->extent_hint);
if (!extent) {
eprintf("process_extents: unable to get extent\n");

Expand Down Expand Up @@ -955,7 +958,7 @@ static int fill_buffer(struct scan_ctxt *ctxt, struct buffer *buffer)
* The entire buffer could be ignored. Let's fast forward
* and mark the buffer as faked
*/
if (is_area_ignored(ctxt->fiemap, ctxt->off, buffer->size)
if (is_area_ignored(ctxt->fiemap, ctxt->off, buffer->size, &ctxt->extent_hint)
&& ctxt->off + buffer->size <= ctxt->filesize) {
memset(buffer->buf, 0, buffer->size);
buffer->dl_len = buffer->size;
Expand Down