Extend packfile in increments of page_size.

This improves performance by reducing the number of I/O operations.

diff --git a/src/indexer.c b/src/indexer.c
index a3a866989e139ae26cad1bff3be7192889a5c25f..67fef1cbc1d6dcbbed9f840048070a367ef2e4da 100644 (file)
--- a/src/indexer.c
+++ b/src/indexer.c
@@ -477,13 +477,29 @@ static int write_at(git_indexer *idx, const void *data, git_off_t offset, size_t
 
 static int append_to_pack(git_indexer *idx, const void *data, size_t size)
 {
+       git_off_t new_size;
+       size_t mmap_alignment;
+       size_t page_offset;
+       git_off_t page_start;
        git_off_t current_size = idx->pack->mwf.size;
        int fd = idx->pack->mwf.fd;
+       int error;
 
        if (!size)
                return 0;
 
-       if (p_lseek(fd, current_size + size - 1, SEEK_SET) < 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_lseek(fd, page_start + mmap_alignment - 1, SEEK_SET) < 0 ||
            p_write(idx->pack->mwf.fd, data, 1) < 0) {
                giterr_set(GITERR_OS, "cannot extend packfile '%s'", idx->pack->pack_name);
                return -1;
@@ -1041,6 +1057,13 @@ int git_indexer_commit(git_indexer *idx, git_transfer_progress *stats)
                goto on_error;
 
        git_mwindow_free_all(&idx->pack->mwf);
+
+       /* Truncate file to undo rounding up to next page_size in append_to_pack */
+       if (p_ftruncate(idx->pack->mwf.fd, idx->pack->mwf.size) < 0) {
+               giterr_set(GITERR_OS, "failed to truncate pack file '%s'", idx->pack->pack_name);
+               return -1;
+       }
+
        /* We need to close the descriptor here so Windows doesn't choke on commit_at */
        if (p_close(idx->pack->mwf.fd) < 0) {
                giterr_set(GITERR_OS, "failed to close packfile");