lkml.org 
[lkml]   [2008]   [Sep]   [12]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    Date
    From
    Subject[PATCH] mm: make do_move_pages() complexity linear
    Page migration is currently very slow because its overhead is quadratic
    with the number of pages. This is caused by each single page migration
    doing a linear lookup in the page array in new_page_node().

    Since pages are stored in the array order in the pagelist and do_move_pages
    process this list in order, new_page_node() can increase the "pm" pointer
    to the page array so that the next iteration will find the next page in
    0 or few lookup steps.

    Signed-off-by: Brice Goglin <Brice.Goglin@inria.fr>
    Signed-off-by: Nathalie Furmento <Nathalie.Furmento@labri.fr>

    --- a/mm/migrate.c
    +++ b/mm/migrate.c
    @@ -837,14 +837,23 @@ struct page_to_node {
    int status;
    };

    +/*
    + * Allocate a page on the node given as a page_to_node in private.
    + * Increase private to point to the next page_to_node so that the
    + * next iteration does not have to traverse the whole pm array.
    + */
    static struct page *new_page_node(struct page *p, unsigned long private,
    int **result)
    {
    - struct page_to_node *pm = (struct page_to_node *)private;
    + struct page_to_node **pmptr = (struct page_to_node **)private;
    + struct page_to_node *pm = *pmptr;

    while (pm->node != MAX_NUMNODES && pm->page != p)
    pm++;

    + /* prepare for the next iteration */
    + *pmptr = pm + 1;
    +
    if (pm->node == MAX_NUMNODES)
    return NULL;

    @@ -926,10 +935,12 @@ set_status:
    pp->status = err;
    }

    - if (!list_empty(&pagelist))
    + if (!list_empty(&pagelist)) {
    + /* new_page_node() will modify tmp */
    + struct page_to_node *tmp = pm;
    err = migrate_pages(&pagelist, new_page_node,
    - (unsigned long)pm);
    - else
    + (unsigned long)&tmp);
    + } else
    err = -ENOENT;

    up_read(&mm->mmap_sem);



    \
     
     \ /
      Last update: 2008-09-12 14:33    [W:0.034 / U:59.896 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site