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    Subject[PATCH] mm/filemap.c: unconditionally call mark_page_accessed

    This patch unconditionally calls mark_page_accessed to prevent pages,
    especially for small files, from being evicted from the page cache despite
    frequent access.

    Signed-off-by: Ashif Harji <>

    If the same page of a file is repeatedly accessed (without accessing other
    pages of that file) via the same file descriptor, mark_page_accessed is
    never called after the first time the page is accessed.

    The implication of this code is that for files of size less than or equal
    to a single page, the page associated with such a file is likely to get
    evicted from the cache regardless of how frequently it is accessed.
    However, this behaviour also occurs with files of any size if the same
    page is repeatedly accessed.

    As a benchmark, I have an experimental web server that uses sendfile to
    repeatedly transmit files. The files are based on the static portion of
    the SPECweb99 fileset and range in size to model a reasonable workload.
    With this workload, a significant number of the requests are for files of
    size 4 KB or less.

    By changing the kernel to always call mark_page_accessed, the server
    throughput is increased by as much as 20%. With one test, for example,
    without the change I get throughput of around 868 Mbps. After making the
    change, performance increases to 1111 Mbps.
    Using a configuration that should be unaffected by the change, performance
    was around 855 Mbps without the change and around 851 Mbps with the
    change. As expected the change had no appreciable effect.

    See thread for additional discussion on
    this change.

    This patch is for kernel version

    Andrew, can you also put this change into the -mm kernels for testing?

    --- linux- 2007-03-14 10:31:58.000000000 -0500
    +++ linux- 2007-03-13 16:11:54.000000000 -0500
    @@ -943,12 +943,7 @@ page_ok:
    if (mapping_writably_mapped(mapping))

    - /*
    - * When (part of) the same page is read multiple times
    - * in succession, only mark it as accessed the first time.
    - */
    - if (prev_index != index)
    - mark_page_accessed(page);
    + mark_page_accessed(page);
    prev_index = index;

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      Last update: 2007-03-14 21:03    [from the cache]
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