Question about buffer size calculation in _php_stream_copy_to_mem_ex View as Markdown

I see the following in _php_stream_copy_to_mem_ex in main/streams/streams.c

int step = CHUNK_SIZE;
int min_room = CHUNK_SIZE / 4;

    (..stuff deleted..)

/* avoid many reallocs by allocating a good sized chunk to begin with, if
 * we can.  Note that the stream may be filtered, in which case the stat
 * result may be inaccurate, as the filter may inflate or deflate the
 * number of bytes that we can read.  In order to avoid an upsize followed
 * by a downsize of the buffer, overestimate by the step size (which is
 * 2K).  */
if (php_stream_stat(src, &ssbuf) == 0 && ssbuf.sb.st_size > 0) {
	max_len = ssbuf.sb.st_size + step;
} else {
	max_len = step;
}

According to the comment the intention is to overestimate by 2K, but
CHUNK_SIZE = 8192 and that leads quite a bit of over-allocation of
memory.

Is the following a better setting for max_len in the if block?

max_len = (((ssbuf.sb.st_size + min_room)/step) + 1) * step;

The following are sample values that show the current vs new size calculation.
ssbuf.sb.st_size, max_len (current), max_len (new)
( 100, 8292, 8192)
( 1000, 9192, 8192)
( 5000, 13192, 8192)
( 7000, 15192, 16384)
( 13000, 21192, 16384)
( 22000, 30192, 24576)

thanks,
arvi