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    Subject[PATCH 3/3] readahead: scale max readahead size depending on memory size
    Scale the default max readahead size with the system memory size.

    Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
    ---
    block/ll_rw_blk.c | 2 +-
    include/linux/fs.h | 1 +
    mm/readahead.c | 32 ++++++++++++++++++++++++++++++++
    3 files changed, 34 insertions(+), 1 deletion(-)

    Index: linux-2.6/block/ll_rw_blk.c
    ===================================================================
    --- linux-2.6.orig/block/ll_rw_blk.c
    +++ linux-2.6/block/ll_rw_blk.c
    @@ -208,7 +208,7 @@ void blk_queue_make_request(request_queu
    blk_queue_max_phys_segments(q, MAX_PHYS_SEGMENTS);
    blk_queue_max_hw_segments(q, MAX_HW_SEGMENTS);
    q->make_request_fn = mfn;
    - q->backing_dev_info.ra_pages = (VM_MAX_READAHEAD * 1024) / PAGE_CACHE_SIZE;
    + bdi_ra_init(&q->backing_dev_info);
    q->backing_dev_info.state = 0;
    q->backing_dev_info.capabilities = BDI_CAP_MAP_COPY;
    blk_queue_max_sectors(q, SAFE_MAX_SECTORS);
    Index: linux-2.6/include/linux/fs.h
    ===================================================================
    --- linux-2.6.orig/include/linux/fs.h
    +++ linux-2.6/include/linux/fs.h
    @@ -1696,6 +1696,7 @@ extern long do_splice_direct(struct file

    extern void
    file_ra_state_init(struct file_ra_state *ra, struct address_space *mapping);
    +extern void bdi_ra_init(struct backing_dev_info *bdi);
    extern loff_t no_llseek(struct file *file, loff_t offset, int origin);
    extern loff_t generic_file_llseek(struct file *file, loff_t offset, int origin);
    extern loff_t remote_llseek(struct file *file, loff_t offset, int origin);
    Index: linux-2.6/mm/readahead.c
    ===================================================================
    --- linux-2.6.orig/mm/readahead.c
    +++ linux-2.6/mm/readahead.c
    @@ -42,6 +42,38 @@ file_ra_state_init(struct file_ra_state
    }
    EXPORT_SYMBOL_GPL(file_ra_state_init);

    +static unsigned long ra_pages;
    +
    +static __init int readahead_init(void)
    +{
    + /*
    + * Scale the max readahead window with system memory
    + *
    + * 64M: 128K
    + * 128M: 180K
    + * 256M: 256K
    + * 512M: 360K
    + * 1G: 512K
    + * 2G: 724K
    + * 4G: 1024K
    + * 8G: 1448K
    + * 16G: 2048K
    + */
    + ra_pages = int_sqrt(totalram_pages/16);
    + if (ra_pages > (2 << (20 - PAGE_SHIFT)))
    + ra_pages = 2 << (20 - PAGE_SHIFT);
    +
    + return 0;
    +}
    +
    +subsys_initcall(readahead_init);
    +
    +void bdi_ra_init(struct backing_dev_info *bdi)
    +{
    + bdi->ra_pages = ra_pages;
    +}
    +EXPORT_SYMBOL(bdi_ra_init);
    +
    #define list_to_page(head) (list_entry((head)->prev, struct page, lru))

    /**
    --

    -
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