Commit 66a75fdee622557346700bae8314ca4af166e0f9
2021-09-07T07:14:39
indexer: Avoid one `mmap(2)`/`munmap(2)` pair per `git_indexer_append` call This change makes `append_to_pack` completely rely on `p_pwrite` to do all its I/O instead of splitting it between `p_pwrite` and a `mmap(2)`/`munmap(2)`+`memcpy(3)`. This saves a good chunk of user CPU time and avoids making two syscalls per round, but doesn't really cut down a lot of wall time (~1% on cloning the [git](https://github.com/git/git.git) repository).
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diff --git a/src/indexer.c b/src/indexer.c
index d546888..a5c282a 100644
--- a/src/indexer.c
+++ b/src/indexer.c
@@ -603,7 +603,6 @@ static void hash_partially(git_indexer *idx, const uint8_t *data, size_t size)
static int write_at(git_indexer *idx, const void *data, off64_t offset, size_t size)
{
-#ifdef NO_MMAP
size_t remaining_size = size;
const char *ptr = (const char *)data;
@@ -619,65 +618,21 @@ static int write_at(git_indexer *idx, const void *data, off64_t offset, size_t s
offset += nb;
remaining_size -= nb;
}
-#else
- git_file fd = idx->pack->mwf.fd;
- size_t mmap_alignment;
- size_t page_offset;
- off64_t page_start;
- unsigned char *map_data;
- git_map map;
- int error;
-
- GIT_ASSERT_ARG(data);
- GIT_ASSERT_ARG(size);
-
- if ((error = git__mmap_alignment(&mmap_alignment)) < 0)
- return error;
-
- /* the offset needs to be at the mmap boundary for the platform */
- page_offset = offset % mmap_alignment;
- page_start = offset - page_offset;
-
- if ((error = p_mmap(&map, page_offset + size, GIT_PROT_WRITE, GIT_MAP_SHARED, fd, page_start)) < 0)
- return error;
-
- map_data = (unsigned char *)map.data;
- memcpy(map_data + page_offset, data, size);
- p_munmap(&map);
-#endif
return 0;
}
static int append_to_pack(git_indexer *idx, const void *data, size_t size)
{
- off64_t new_size;
- size_t mmap_alignment;
- size_t page_offset;
- off64_t page_start;
- off64_t current_size = idx->pack->mwf.size;
- int error;
-
if (!size)
return 0;
- if ((error = git__mmap_alignment(&mmap_alignment)) < 0)
- return error;
-
- /* Write a single byte to force the file system to allocate space now or
- * report an error, since we can't report errors when writing using mmap.
- * Round the size up to the nearest page so that we only need to perform file
- * I/O when we add a page, instead of whenever we write even a single byte. */
- new_size = current_size + size;
- page_offset = new_size % mmap_alignment;
- page_start = new_size - page_offset;
-
- if (p_pwrite(idx->pack->mwf.fd, data, 1, page_start + mmap_alignment - 1) < 0) {
+ if (write_at(idx, data, idx->pack->mwf.size, size) < 0) {
git_error_set(GIT_ERROR_OS, "cannot extend packfile '%s'", idx->pack->pack_name);
return -1;
}
- return write_at(idx, data, idx->pack->mwf.size, size);
+ return 0;
}
static int read_stream_object(git_indexer *idx, git_indexer_progress *stats)