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    Subject[patch 1/3] vmscan: factor out page reference checks
    Date
    Moving the big conditional into its own predicate function makes the
    code a bit easier to read and allows for better commenting on the
    checks one-by-one.

    This is just cleaning up, no semantics should have been changed.

    Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
    ---
    mm/vmscan.c | 53 ++++++++++++++++++++++++++++++++++++++++-------------
    1 files changed, 40 insertions(+), 13 deletions(-)

    diff --git a/mm/vmscan.c b/mm/vmscan.c
    index c26986c..c2db55b 100644
    --- a/mm/vmscan.c
    +++ b/mm/vmscan.c
    @@ -579,6 +579,37 @@ redo:
    put_page(page); /* drop ref from isolate */
    }

    +enum page_references {
    + PAGEREF_RECLAIM,
    + PAGEREF_RECLAIM_CLEAN,
    + PAGEREF_ACTIVATE,
    +};
    +
    +static enum page_references page_check_references(struct page *page,
    + struct scan_control *sc)
    +{
    + unsigned long vm_flags;
    + int referenced;
    +
    + referenced = page_referenced(page, 1, sc->mem_cgroup, &vm_flags);
    + if (!referenced)
    + return PAGEREF_RECLAIM;
    +
    + /* Lumpy reclaim - ignore references */
    + if (sc->order > PAGE_ALLOC_COSTLY_ORDER)
    + return PAGEREF_RECLAIM;
    +
    + /* Mlock lost isolation race - let try_to_unmap() handle it */
    + if (vm_flags & VM_LOCKED)
    + return PAGEREF_RECLAIM;
    +
    + if (page_mapping_inuse(page))
    + return PAGEREF_ACTIVATE;
    +
    + /* Reclaim if clean, defer dirty pages to writeback */
    + return PAGEREF_RECLAIM_CLEAN;
    +}
    +
    /*
    * shrink_page_list() returns the number of reclaimed pages
    */
    @@ -590,16 +621,15 @@ static unsigned long shrink_page_list(struct list_head *page_list,
    struct pagevec freed_pvec;
    int pgactivate = 0;
    unsigned long nr_reclaimed = 0;
    - unsigned long vm_flags;

    cond_resched();

    pagevec_init(&freed_pvec, 1);
    while (!list_empty(page_list)) {
    + enum page_references references;
    struct address_space *mapping;
    struct page *page;
    int may_enter_fs;
    - int referenced;

    cond_resched();

    @@ -641,17 +671,14 @@ static unsigned long shrink_page_list(struct list_head *page_list,
    goto keep_locked;
    }

    - referenced = page_referenced(page, 1,
    - sc->mem_cgroup, &vm_flags);
    - /*
    - * In active use or really unfreeable? Activate it.
    - * If page which have PG_mlocked lost isoltation race,
    - * try_to_unmap moves it to unevictable list
    - */
    - if (sc->order <= PAGE_ALLOC_COSTLY_ORDER &&
    - referenced && page_mapping_inuse(page)
    - && !(vm_flags & VM_LOCKED))
    + references = page_check_references(page, sc);
    + switch (references) {
    + case PAGEREF_ACTIVATE:
    goto activate_locked;
    + case PAGEREF_RECLAIM:
    + case PAGEREF_RECLAIM_CLEAN:
    + ; /* try to reclaim the page below */
    + }

    /*
    * Anonymous process memory has backing store?
    @@ -685,7 +712,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
    }

    if (PageDirty(page)) {
    - if (sc->order <= PAGE_ALLOC_COSTLY_ORDER && referenced)
    + if (references == PAGEREF_RECLAIM_CLEAN)
    goto keep_locked;
    if (!may_enter_fs)
    goto keep_locked;
    --
    1.6.6.1


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