RFC optimisation of file.c read size

@@ -533,18 +558,22 @@ static struct pike_string *do_read(int fd, /* For some reason, 8k seems to work faster than 64k. * (4k seems to be about 2% faster than 8k when using linux though) * /Hubbe (Per pointed it out to me..)

• *
  

• * The slowdowns most likely are because of memory validation
  

• * done by the kernel for buffer space which is later unused
  

• * (short read)
  */
  

Feel free to follow style with a /srb or similar; it's actually both useful and makes the in-comment discussions nicer to read, even though "blame" can be used to track down the same data with moderate accuracy too when really needed. (Hardly a general rule, but felt appropriate.)

(Not meant as policy nit, as there is none; do as you well prefer. :-)