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    Subject[patch 10/10] mm: memcg: remove unused node/section info from pc->flags
    Date
    To find the page corresponding to a certain page_cgroup, the pc->flags
    encoded the node or section ID with the base array to compare the pc
    pointer to.

    Now that the per-memory cgroup LRU lists link page descriptors
    directly, there is no longer any code that knows the struct
    page_cgroup of a PFN but not the struct page.

    Signed-off-by: Johannes Weiner <jweiner@redhat.com>
    Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
    Reviewed-by: Michal Hocko <mhocko@suse.cz>
    Reviewed-by: Kirill A. Shutemov <kirill@shutemov.name>
    ---
    include/linux/page_cgroup.h | 33 ------------------------
    mm/page_cgroup.c | 58 ++++++-------------------------------------
    2 files changed, 8 insertions(+), 83 deletions(-)

    diff --git a/include/linux/page_cgroup.h b/include/linux/page_cgroup.h
    index 5bae753..aaa60da 100644
    --- a/include/linux/page_cgroup.h
    +++ b/include/linux/page_cgroup.h
    @@ -121,39 +121,6 @@ static inline void move_unlock_page_cgroup(struct page_cgroup *pc,
    local_irq_restore(*flags);
    }

    -#ifdef CONFIG_SPARSEMEM
    -#define PCG_ARRAYID_WIDTH SECTIONS_SHIFT
    -#else
    -#define PCG_ARRAYID_WIDTH NODES_SHIFT
    -#endif
    -
    -#if (PCG_ARRAYID_WIDTH > BITS_PER_LONG - NR_PCG_FLAGS)
    -#error Not enough space left in pc->flags to store page_cgroup array IDs
    -#endif
    -
    -/* pc->flags: ARRAY-ID | FLAGS */
    -
    -#define PCG_ARRAYID_MASK ((1UL << PCG_ARRAYID_WIDTH) - 1)
    -
    -#define PCG_ARRAYID_OFFSET (BITS_PER_LONG - PCG_ARRAYID_WIDTH)
    -/*
    - * Zero the shift count for non-existent fields, to prevent compiler
    - * warnings and ensure references are optimized away.
    - */
    -#define PCG_ARRAYID_SHIFT (PCG_ARRAYID_OFFSET * (PCG_ARRAYID_WIDTH != 0))
    -
    -static inline void set_page_cgroup_array_id(struct page_cgroup *pc,
    - unsigned long id)
    -{
    - pc->flags &= ~(PCG_ARRAYID_MASK << PCG_ARRAYID_SHIFT);
    - pc->flags |= (id & PCG_ARRAYID_MASK) << PCG_ARRAYID_SHIFT;
    -}
    -
    -static inline unsigned long page_cgroup_array_id(struct page_cgroup *pc)
    -{
    - return (pc->flags >> PCG_ARRAYID_SHIFT) & PCG_ARRAYID_MASK;
    -}
    -
    #else /* CONFIG_CGROUP_MEM_RES_CTLR */
    struct page_cgroup;

    diff --git a/mm/page_cgroup.c b/mm/page_cgroup.c
    index 256dee8..2601a65 100644
    --- a/mm/page_cgroup.c
    +++ b/mm/page_cgroup.c
    @@ -11,12 +11,6 @@
    #include <linux/swapops.h>
    #include <linux/kmemleak.h>

    -static void __meminit init_page_cgroup(struct page_cgroup *pc, unsigned long id)
    -{
    - pc->flags = 0;
    - set_page_cgroup_array_id(pc, id);
    - pc->mem_cgroup = NULL;
    -}
    static unsigned long total_usage;

    #if !defined(CONFIG_SPARSEMEM)
    @@ -41,24 +35,11 @@ struct page_cgroup *lookup_page_cgroup(struct page *page)
    return base + offset;
    }

    -struct page *lookup_cgroup_page(struct page_cgroup *pc)
    -{
    - unsigned long pfn;
    - struct page *page;
    - pg_data_t *pgdat;
    -
    - pgdat = NODE_DATA(page_cgroup_array_id(pc));
    - pfn = pc - pgdat->node_page_cgroup + pgdat->node_start_pfn;
    - page = pfn_to_page(pfn);
    - VM_BUG_ON(pc != lookup_page_cgroup(page));
    - return page;
    -}
    -
    static int __init alloc_node_page_cgroup(int nid)
    {
    - struct page_cgroup *base, *pc;
    + struct page_cgroup *base;
    unsigned long table_size;
    - unsigned long start_pfn, nr_pages, index;
    + unsigned long nr_pages;

    start_pfn = NODE_DATA(nid)->node_start_pfn;
    nr_pages = NODE_DATA(nid)->node_spanned_pages;
    @@ -72,10 +53,6 @@ static int __init alloc_node_page_cgroup(int nid)
    table_size, PAGE_SIZE, __pa(MAX_DMA_ADDRESS));
    if (!base)
    return -ENOMEM;
    - for (index = 0; index < nr_pages; index++) {
    - pc = base + index;
    - init_page_cgroup(pc, nid);
    - }
    NODE_DATA(nid)->node_page_cgroup = base;
    total_usage += table_size;
    return 0;
    @@ -116,31 +93,19 @@ struct page_cgroup *lookup_page_cgroup(struct page *page)
    return section->page_cgroup + pfn;
    }

    -struct page *lookup_cgroup_page(struct page_cgroup *pc)
    -{
    - struct mem_section *section;
    - struct page *page;
    - unsigned long nr;
    -
    - nr = page_cgroup_array_id(pc);
    - section = __nr_to_section(nr);
    - page = pfn_to_page(pc - section->page_cgroup);
    - VM_BUG_ON(pc != lookup_page_cgroup(page));
    - return page;
    -}
    -
    static void *__meminit alloc_page_cgroup(size_t size, int nid)
    {
    void *addr = NULL;

    - addr = alloc_pages_exact_nid(nid, size, GFP_KERNEL | __GFP_NOWARN);
    + addr = alloc_pages_exact_nid(nid, size,
    + GFP_KERNEL | __GFP_ZERO | __GFP_NOWARN);
    if (addr)
    return addr;

    if (node_state(nid, N_HIGH_MEMORY))
    - addr = vmalloc_node(size, nid);
    + addr = vzalloc_node(size, nid);
    else
    - addr = vmalloc(size);
    + addr = vzalloc(size);

    return addr;
    }
    @@ -163,14 +128,11 @@ static void free_page_cgroup(void *addr)

    static int __meminit init_section_page_cgroup(unsigned long pfn, int nid)
    {
    - struct page_cgroup *base, *pc;
    struct mem_section *section;
    + struct page_cgroup *base;
    unsigned long table_size;
    - unsigned long nr;
    - int index;

    - nr = pfn_to_section_nr(pfn);
    - section = __nr_to_section(nr);
    + section = __pfn_to_section(pfn);

    if (section->page_cgroup)
    return 0;
    @@ -190,10 +152,6 @@ static int __meminit init_section_page_cgroup(unsigned long pfn, int nid)
    return -ENOMEM;
    }

    - for (index = 0; index < PAGES_PER_SECTION; index++) {
    - pc = base + index;
    - init_page_cgroup(pc, nr);
    - }
    /*
    * The passed "pfn" may not be aligned to SECTION. For the calculation
    * we need to apply a mask.
    --
    1.7.6.2


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