Re: [parisc-linux] Re: Problems with kernel mmap (failing tst-mmap-eofsync in glibc on parisc)

From: James Bottomley (James.Bottomley_at_steeleye.com)
Date: 08/23/03

  • Next message: Erik Andersen: "[PATCH] Fix cdrom error handling in 2.6" 
    To: "David S. Miller" <davem@redhat.com>
Date:	22 Aug 2003 20:09:30 -0500

    On Fri, 2003-08-22 at 17:41, David S. Miller wrote:
    > I think on parisc you are trying to avoid the write() case
    > of the cache flush for non-shared mmap()s, and sorry you
    > really can't do this, again this is:
    >
    > When a write() system call occurs, the kernel "class" is writing to
    > the page so all user mappings (shared or not!) need to be flushed
    > out.
    >
    > If your flush_dcache_page() is not doing this, it's no wonder
    > the test case fails for you.

    Yes, that's precisely what we're trying to do. Our problem is that we
    have to issue the flush to all the aliased addresses (one cache line at
    a time) which is phenomenally expensive.

    What we were hoping is that we could rely on this little property of
    mmap:

           MAP_PRIVATE
                      Create a private copy-on-write mapping. Stores
                      to the region do not affect the original file.
                      It is unspecified whether changes made to the
                      file after the mmap call are visible in the
                      mapped region.

    To avoid having to flush the non-shared mappings (basically on parisc if
    you write to a file backing a MAP_PRIVATE mapping then we don't
    guarantee you see the update).

    I suppose if we had a way of telling if any of the i_mmap list members
    were really MAP_SHARED semantics mappings, then we could alter our
    flush_dcache_page() implementation to work.

    James

    -
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to majordomo@vger.kernel.org
    More majordomo info at http://vger.kernel.org/majordomo-info.html
    Please read the FAQ at http://www.tux.org/lkml/

  • Next message: Erik Andersen: "[PATCH] Fix cdrom error handling in 2.6"