In some places the IO library simply assumes that the IO request is 'small enough', and happily allocates a buffer big enough for the request to be handled in one go. Unformatted IO already uses sread()/swrite() which bypasses buffering if the request is bigger than the buffer size. However, this has not been done for formatted IO. In some cases this results in excessive memory usage. A rather extreme (and admittedly contrived) example is program bigformdir integer :: i = 10**9 open (10, file="foo", form="formatted", access="direct", recl=i) write (10, '(i3)', rec=1) 1 close (10) end program bigformdir The above program will cause libgfortran to allocate 1 GB, fill it with ' ', and then write it. Clearly the allocation is not necessary.
It is even worse when opening two of these :) (or even five). Confirmed.
Patch here: http://gcc.gnu.org/ml/gcc-patches/2006-01/msg01765.html
Subject: Bug 25949 Author: jb Date: Sun Feb 12 19:59:32 2006 New Revision: 110895 URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=110895 Log: 2006-02-12 Janne Blomqvist <jb@gcc.gnu.org> PR libgfortran/25949 * io/io.h: Add set function pointer to struct stream. * io/unix.c (fd_seek): Only update offset, don't seek. (fd_sset): New function. (fd_read): Call lseek directly if necessary. (fd_write): Likewise. (fd_open): Set pointer to fd_sset. (mem_set): New function. (open_internal): Set pointer to mem_set. * io/transfer.c (write_block_direct): Rename to write_buf, add error return, non-pointer length argument. (unformatted_write): Update to use write_buf. (us_write): Simplify by using swrite instead of salloc_w. (write_us_marker): New function. (new_record_w): Use sset instead of memset, use write_us_marker, simplify by using swrite instead of salloc_w. Modified: trunk/libgfortran/ChangeLog trunk/libgfortran/io/io.h trunk/libgfortran/io/transfer.c trunk/libgfortran/io/unix.c
Subject: Bug 25949 Author: jb Date: Tue Feb 14 20:21:15 2006 New Revision: 110995 URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=110995 Log: 2006-02-14 Janne Blomqvist <jb@gcc.gnu.org> PR libgfortran/25949 * io/io.h: Add set function pointer to struct stream. * io/unix.c (fd_seek): Only update offset, don't seek. (fd_sset): New function. (fd_read): Call lseek directly if necessary. (fd_write): Likewise. (fd_open): Set pointer to fd_sset. (mem_set): New function. (open_internal): Set pointer to mem_set. * io/transfer.c (write_block_direct): Rename to write_buf, add error return, non-pointer length argument. (unformatted_write): Update to use write_buf. (us_write): Simplify by using swrite instead of salloc_w. (write_us_marker): New function. (new_record_w): Use sset instead of memset, use write_us_marker, simplify by using swrite instead of salloc_w. Modified: branches/gcc-4_1-branch/libgfortran/ChangeLog branches/gcc-4_1-branch/libgfortran/io/io.h branches/gcc-4_1-branch/libgfortran/io/transfer.c branches/gcc-4_1-branch/libgfortran/io/unix.c
I think we can close this one, now, can't we?