upload: change default UPLOAD_BUFSIZE to 64KB

To make uploads significantly faster in some circumstances.

Part 2 of #2888
Closes #2892

2 files changed, 8 insertions, 3 deletions

diff --git a/lib/transfer.c b/lib/transfer.c
index 96d8ab48f..ab9094adc 100644
--- a/lib/transfer.c
+++ b/lib/transfer.c
@@ -992,7 +992,7 @@ static CURLcode readwrite_upload(struct Curl_easy *data,
          (data->set.crlf))) {
         /* Do we need to allocate a scratch buffer? */
         if(!data->state.scratch) {
-          data->state.scratch = malloc(2 * data->set.buffer_size);
+          data->state.scratch = malloc(2 * UPLOAD_BUFSIZE);
           if(!data->state.scratch) {
             failf(data, "Failed to alloc scratch buffer!");
 
diff --git a/lib/urldata.h b/lib/urldata.h
index 502cff362..67db3b2fc 100644
--- a/lib/urldata.h
+++ b/lib/urldata.h
@@ -143,8 +143,13 @@ typedef ssize_t (Curl_recv)(struct connectdata *conn, /* connection data */
 #endif /* HAVE_LIBSSH2_H */
 
 /* The upload buffer size, should not be smaller than CURL_MAX_WRITE_SIZE, as
-   it needs to hold a full buffer as could be sent in a write callback */
-#define UPLOAD_BUFSIZE CURL_MAX_WRITE_SIZE
+   it needs to hold a full buffer as could be sent in a write callback.
+
+   The size was 16KB for many years but was bumped to 64KB because it makes
+   libcurl able to do significantly faster uploads in some circumstances. Even
+   larger buffers can help further, but this is deemed a fair memory/speed
+   compromise. */
+#define UPLOAD_BUFSIZE 65536
 
 /* The "master buffer" is for HTTP pipelining */
 #define MASTERBUF_SIZE 16384