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    Subject[PATCH 11/14] mm: memcontrol: do not account memory+swap on unified hierarchy
    Date
    The unified hierarchy memory controller doesn't expose the memory+swap
    counter to userspace, but its accounting is hardcoded in all charge
    paths right now, including the per-cpu charge cache ("the stock").

    To avoid adding yet more pointless memory+swap accounting with the
    socket memory support in unified hierarchy, disable the counter
    altogether when in unified hierarchy mode.

    Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
    ---
    mm/memcontrol.c | 44 +++++++++++++++++++++++++-------------------
    1 file changed, 25 insertions(+), 19 deletions(-)

    diff --git a/mm/memcontrol.c b/mm/memcontrol.c
    index 658bef2..e7f1a79 100644
    --- a/mm/memcontrol.c
    +++ b/mm/memcontrol.c
    @@ -87,6 +87,12 @@ int do_swap_account __read_mostly;
    #define do_swap_account 0
    #endif

    +/* Whether legacy memory+swap accounting is active */
    +static bool do_memsw_account(void)
    +{
    + return !cgroup_subsys_on_dfl(memory_cgrp_subsys) && do_swap_account;
    +}
    +
    static const char * const mem_cgroup_stat_names[] = {
    "cache",
    "rss",
    @@ -1177,7 +1183,7 @@ static unsigned long mem_cgroup_margin(struct mem_cgroup *memcg)
    if (count < limit)
    margin = limit - count;

    - if (do_swap_account) {
    + if (do_memsw_account()) {
    count = page_counter_read(&memcg->memsw);
    limit = READ_ONCE(memcg->memsw.limit);
    if (count <= limit)
    @@ -1280,7 +1286,7 @@ void mem_cgroup_print_oom_info(struct mem_cgroup *memcg, struct task_struct *p)
    pr_cont(":");

    for (i = 0; i < MEM_CGROUP_STAT_NSTATS; i++) {
    - if (i == MEM_CGROUP_STAT_SWAP && !do_swap_account)
    + if (i == MEM_CGROUP_STAT_SWAP && !do_memsw_account())
    continue;
    pr_cont(" %s:%luKB", mem_cgroup_stat_names[i],
    K(mem_cgroup_read_stat(iter, i)));
    @@ -1903,7 +1909,7 @@ static void drain_stock(struct memcg_stock_pcp *stock)

    if (stock->nr_pages) {
    page_counter_uncharge(&old->memory, stock->nr_pages);
    - if (do_swap_account)
    + if (do_memsw_account())
    page_counter_uncharge(&old->memsw, stock->nr_pages);
    css_put_many(&old->css, stock->nr_pages);
    stock->nr_pages = 0;
    @@ -2033,11 +2039,11 @@ retry:
    if (consume_stock(memcg, nr_pages))
    return 0;

    - if (!do_swap_account ||
    + if (!do_memsw_account() ||
    page_counter_try_charge(&memcg->memsw, batch, &counter)) {
    if (page_counter_try_charge(&memcg->memory, batch, &counter))
    goto done_restock;
    - if (do_swap_account)
    + if (do_memsw_account())
    page_counter_uncharge(&memcg->memsw, batch);
    mem_over_limit = mem_cgroup_from_counter(counter, memory);
    } else {
    @@ -2124,7 +2130,7 @@ force:
    * temporarily by force charging it.
    */
    page_counter_charge(&memcg->memory, nr_pages);
    - if (do_swap_account)
    + if (do_memsw_account())
    page_counter_charge(&memcg->memsw, nr_pages);
    css_get_many(&memcg->css, nr_pages);

    @@ -2161,7 +2167,7 @@ static void cancel_charge(struct mem_cgroup *memcg, unsigned int nr_pages)
    return;

    page_counter_uncharge(&memcg->memory, nr_pages);
    - if (do_swap_account)
    + if (do_memsw_account())
    page_counter_uncharge(&memcg->memsw, nr_pages);

    css_put_many(&memcg->css, nr_pages);
    @@ -2441,7 +2447,7 @@ void __memcg_kmem_uncharge(struct page *page, int order)

    page_counter_uncharge(&memcg->kmem, nr_pages);
    page_counter_uncharge(&memcg->memory, nr_pages);
    - if (do_swap_account)
    + if (do_memsw_account())
    page_counter_uncharge(&memcg->memsw, nr_pages);

    page->mem_cgroup = NULL;
    @@ -3154,7 +3160,7 @@ static int memcg_stat_show(struct seq_file *m, void *v)
    BUILD_BUG_ON(ARRAY_SIZE(mem_cgroup_lru_names) != NR_LRU_LISTS);

    for (i = 0; i < MEM_CGROUP_STAT_NSTATS; i++) {
    - if (i == MEM_CGROUP_STAT_SWAP && !do_swap_account)
    + if (i == MEM_CGROUP_STAT_SWAP && !do_memsw_account())
    continue;
    seq_printf(m, "%s %lu\n", mem_cgroup_stat_names[i],
    mem_cgroup_read_stat(memcg, i) * PAGE_SIZE);
    @@ -3176,14 +3182,14 @@ static int memcg_stat_show(struct seq_file *m, void *v)
    }
    seq_printf(m, "hierarchical_memory_limit %llu\n",
    (u64)memory * PAGE_SIZE);
    - if (do_swap_account)
    + if (do_memsw_account())
    seq_printf(m, "hierarchical_memsw_limit %llu\n",
    (u64)memsw * PAGE_SIZE);

    for (i = 0; i < MEM_CGROUP_STAT_NSTATS; i++) {
    unsigned long long val = 0;

    - if (i == MEM_CGROUP_STAT_SWAP && !do_swap_account)
    + if (i == MEM_CGROUP_STAT_SWAP && !do_memsw_account())
    continue;
    for_each_mem_cgroup_tree(mi, memcg)
    val += mem_cgroup_read_stat(mi, i) * PAGE_SIZE;
    @@ -3314,7 +3320,7 @@ static void mem_cgroup_threshold(struct mem_cgroup *memcg)
    {
    while (memcg) {
    __mem_cgroup_threshold(memcg, false);
    - if (do_swap_account)
    + if (do_memsw_account())
    __mem_cgroup_threshold(memcg, true);

    memcg = parent_mem_cgroup(memcg);
    @@ -4460,7 +4466,7 @@ static struct page *mc_handle_swap_pte(struct vm_area_struct *vma,
    * we call find_get_page() with swapper_space directly.
    */
    page = find_get_page(swap_address_space(ent), ent.val);
    - if (do_swap_account)
    + if (do_memsw_account())
    entry->val = ent.val;

    return page;
    @@ -4495,7 +4501,7 @@ static struct page *mc_handle_file_pte(struct vm_area_struct *vma,
    page = find_get_entry(mapping, pgoff);
    if (radix_tree_exceptional_entry(page)) {
    swp_entry_t swp = radix_to_swp_entry(page);
    - if (do_swap_account)
    + if (do_memsw_account())
    *entry = swp;
    page = find_get_page(swap_address_space(swp), swp.val);
    }
    @@ -5270,7 +5276,7 @@ int mem_cgroup_try_charge(struct page *page, struct mm_struct *mm,
    if (page->mem_cgroup)
    goto out;

    - if (do_swap_account) {
    + if (do_memsw_account()) {
    swp_entry_t ent = { .val = page_private(page), };
    unsigned short id = lookup_swap_cgroup_id(ent);

    @@ -5334,7 +5340,7 @@ void mem_cgroup_commit_charge(struct page *page, struct mem_cgroup *memcg,
    memcg_check_events(memcg, page);
    local_irq_enable();

    - if (do_swap_account && PageSwapCache(page)) {
    + if (do_memsw_account() && PageSwapCache(page)) {
    swp_entry_t entry = { .val = page_private(page) };
    /*
    * The swap entry might not get freed for a long time,
    @@ -5379,7 +5385,7 @@ static void uncharge_batch(struct mem_cgroup *memcg, unsigned long pgpgout,

    if (!mem_cgroup_is_root(memcg)) {
    page_counter_uncharge(&memcg->memory, nr_pages);
    - if (do_swap_account)
    + if (do_memsw_account())
    page_counter_uncharge(&memcg->memsw, nr_pages);
    memcg_oom_recover(memcg);
    }
    @@ -5587,7 +5593,7 @@ void mem_cgroup_swapout(struct page *page, swp_entry_t entry)
    VM_BUG_ON_PAGE(PageLRU(page), page);
    VM_BUG_ON_PAGE(page_count(page), page);

    - if (!do_swap_account)
    + if (!do_memsw_account())
    return;

    memcg = page->mem_cgroup;
    @@ -5627,7 +5633,7 @@ void mem_cgroup_uncharge_swap(swp_entry_t entry)
    struct mem_cgroup *memcg;
    unsigned short id;

    - if (!do_swap_account)
    + if (!do_memsw_account())
    return;

    id = swap_cgroup_record(entry, 0);
    --
    2.6.2


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