[bug #17903] cp/mv only read/write 512 byte blocks when filesystem blksize > 4MB

[Tony Ernst]

URL:
  <http://savannah.gnu.org/bugs/?17903>

                 Summary: cp/mv only read/write 512 byte blocks when
filesystem blksize > 4MB
                 Project: GNU Core Utilities
            Submitted by: tonyernst
            Submitted on: Monday 10/02/2006 at 20:29
                Category: None
                Severity: 3 - Normal
              Item Group: None
                  Status: None
                 Privacy: Public
             Assigned to: None
             Open/Closed: Open

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Details:

A user is complaining about serious performance problems after upgrading
their system.  I found that this was due to the following change in the
coreutils source file system.h:

coreutils-4.5.3:

#else /* HAVE_STRUCT_STAT_ST_BLOCKS */
/* Some systems, like Sequents, return st_blksize of 0 on pipes. */
# define ST_BLKSIZE(statbuf) ((statbuf).st_blksize > 0 \
                               ? (statbuf).st_blksize : DEV_BSIZE)

coreutils-5.2.1:

#else /* HAVE_STRUCT_STAT_ST_BLOCKS */
/* Some systems, like Sequents, return st_blksize of 0 on pipes.
   Also, when running `rsh hpux11-system cat any-file', cat would
   determine that the output stream had an st_blksize of 2147421096.
   So here we arbitrarily limit the `optimal' block size to 4MB.
   If anyone knows of a system for which the legitimate value for
   st_blksize can exceed 4MB, please report it as a bug in this code.  */
# define ST_BLKSIZE(statbuf) ((0 < (statbuf).st_blksize \
                               && (statbuf).st_blksize <= (1 << 22)) /* 4MB
*/ \
                              ? (statbuf).st_blksize : DEV_BSIZE)

XFS filesystems can have legitimate st_blksize values that greatly exceed
4MB.

In the case of the user I referred to above, their st_blksize was 6MB.  With
coreutils-4.5.3, they saw 6MB reads/writes.  With coreutils-5.2.1, the
reads/writes were all 512-bytes.







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