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    Subject[PATCH] mm: add config for readahead window
    Date
    From: Wei Wang <wvw@google.com>

    Change VM_MAX_READAHEAD value from the default 128KB to a configurable
    value. This will allow the readahead window to grow to a maximum size
    bigger than 128KB during boot, which could benefit to sequential read
    throughput and thus boot performance.

    Signed-off-by: Wei Wang <wvw@google.com>
    ---
    include/linux/mm.h | 2 +-
    mm/Kconfig | 8 ++++++++
    2 files changed, 9 insertions(+), 1 deletion(-)

    diff --git a/include/linux/mm.h b/include/linux/mm.h
    index ad06d42adb1a..d7dc6125833e 100644
    --- a/include/linux/mm.h
    +++ b/include/linux/mm.h
    @@ -2291,7 +2291,7 @@ int __must_check write_one_page(struct page *page);
    void task_dirty_inc(struct task_struct *tsk);

    /* readahead.c */
    -#define VM_MAX_READAHEAD 128 /* kbytes */
    +#define VM_MAX_READAHEAD CONFIG_VM_MAX_READAHEAD_KB
    #define VM_MIN_READAHEAD 16 /* kbytes (includes current page) */

    int force_page_cache_readahead(struct address_space *mapping, struct file *filp,
    diff --git a/mm/Kconfig b/mm/Kconfig
    index c782e8fb7235..da9ff543bdb9 100644
    --- a/mm/Kconfig
    +++ b/mm/Kconfig
    @@ -760,3 +760,11 @@ config GUP_BENCHMARK
    performance of get_user_pages_fast().

    See tools/testing/selftests/vm/gup_benchmark.c
    +
    +config VM_MAX_READAHEAD_KB
    + int "Default max readahead window size in Kilobytes"
    + default 128
    + help
    + This sets the VM_MAX_READAHEAD value to allow the readahead window
    + to grow to a maximum size of configured. Increasing this value will
    + benefit sequential read throughput.
    --
    2.16.2.804.g6dcf76e118-goog
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