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    Subject[PATCH prototype] [3/8] Make readahead max pinned value a sysctl
    Date

    Previously it was hard coded to 2MB, which seems dubious as systems
    are getting more and more memory. With a sysctl it is easier to play
    around with it and tune it.

    Signed-off-by: Andi Kleen <andi@firstfloor.org>

    ---
    include/linux/mm.h | 2 ++
    kernel/sysctl.c | 10 ++++++++++
    mm/readahead.c | 14 ++++++++++++--
    3 files changed, 24 insertions(+), 2 deletions(-)

    Index: linux/mm/readahead.c
    ===================================================================
    --- linux.orig/mm/readahead.c
    +++ linux/mm/readahead.c
    @@ -17,6 +17,14 @@
    #include <linux/pagevec.h>
    #include <linux/pagemap.h>

    +/*
    + * Max memory pinned during forced readahead.
    + * Should be probably auto scaled with available memory.
    + */
    +unsigned ra_max_pinned = 2*1024*1024;
    +
    +#define MAX_PINNED_CHUNK ra_max_pinned
    +
    void default_unplug_io_fn(struct backing_dev_info *bdi, struct page *page)
    {
    }
    @@ -176,7 +184,7 @@ out:
    }

    /*
    - * Chunk the readahead into 2 megabyte units, so that we don't pin too much
    + * Chunk the readahead into MAX_PINNED_CHUNK units, so that we don't pin too much
    * memory at once.
    */
    int force_page_cache_readahead(struct address_space *mapping, struct file *filp,
    @@ -190,7 +198,7 @@ int force_page_cache_readahead(struct ad
    while (nr_to_read) {
    int err;

    - unsigned long this_chunk = (2 * 1024 * 1024) / PAGE_CACHE_SIZE;
    + unsigned long this_chunk = MAX_PINNED_CHUNK / PAGE_CACHE_SIZE;

    if (this_chunk > nr_to_read)
    this_chunk = nr_to_read;
    @@ -229,6 +237,8 @@ int do_page_cache_readahead(struct addre
    */
    unsigned long max_sane_readahead(unsigned long nr)
    {
    + /* AK: RED-PEN for file cached pages there is no reason
    + to limit ourselves to the current node */
    return min(nr, (node_page_state(numa_node_id(), NR_INACTIVE)
    + node_page_state(numa_node_id(), NR_FREE_PAGES)) / 2);
    }
    Index: linux/include/linux/mm.h
    ===================================================================
    --- linux.orig/include/linux/mm.h
    +++ linux/include/linux/mm.h
    @@ -1113,6 +1113,8 @@ void page_cache_async_readahead(struct a

    unsigned long max_sane_readahead(unsigned long nr);

    +extern unsigned ra_max_pinned;
    +
    /* Do stack extension */
    extern int expand_stack(struct vm_area_struct *vma, unsigned long address);
    #ifdef CONFIG_IA64
    Index: linux/kernel/sysctl.c
    ===================================================================
    --- linux.orig/kernel/sysctl.c
    +++ linux/kernel/sysctl.c
    @@ -877,6 +877,16 @@ static struct ctl_table vm_table[] = {
    .proc_handler = &proc_dointvec,
    },
    {
    + .ctl_name = CTL_UNNUMBERED,
    + .procname = "ra_max_pinned",
    + .data = &ra_max_pinned,
    + .maxlen = sizeof(ra_max_pinned),
    + .mode = 0644,
    + .proc_handler = &proc_dointvec,
    + .strategy = &sysctl_intvec,
    + .extra1 = &zero,
    + },
    + {
    .ctl_name = VM_DIRTY_BACKGROUND,
    .procname = "dirty_background_ratio",
    .data = &dirty_background_ratio,

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