Re: [RFC PATCH 2/3] memcg-v1: remove charge move code

Michal Hocko
2024-10-24T09:14:47Z

On Wed 23-10-24 23:57:11, Shakeel Butt wrote:
> The memcg-v1 charge move feature has been deprecated completely and
> let's remove the relevant code as well.
>
> Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev>

Acked-by: Michal Hocko <mhocko@suse.com>
> ---
> include/linux/memcontrol.h | 5 -
> mm/memcontrol-v1.c | 864 -------------------------------------
> mm/memcontrol-v1.h | 6 -
> mm/memcontrol.c | 9 -
> 4 files changed, 884 deletions(-)
>
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 524006313b0d..798db70b0a30 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -299,11 +299,6 @@ struct mem_cgroup {
> /* For oom notifier event fd */
> struct list_head oom_notify;
>
> - /*
> - * Should we move charges of a task when a task is moved into this
> - * mem_cgroup ? And what type of charges should we move ?
> - */
> - unsigned long move_charge_at_immigrate;
> /* taken only while moving_account > 0 */
> spinlock_t move_lock;
> unsigned long move_lock_flags;
> diff --git a/mm/memcontrol-v1.c b/mm/memcontrol-v1.c
> index 8f88540f0159..79339cb65b9d 100644
> --- a/mm/memcontrol-v1.c
> +++ b/mm/memcontrol-v1.c
> @@ -40,31 +40,6 @@ static struct mem_cgroup_tree soft_limit_tree __read_mostly;
> #define MEM_CGROUP_MAX_RECLAIM_LOOPS 100
> #define MEM_CGROUP_MAX_SOFT_LIMIT_RECLAIM_LOOPS 2
>
> -/* Stuffs for move charges at task migration. */
> -/*
> - * Types of charges to be moved.
> - */
> -#define MOVE_ANON 0x1ULL
> -#define MOVE_FILE 0x2ULL
> -#define MOVE_MASK (MOVE_ANON | MOVE_FILE)
> -
> -/* "mc" and its members are protected by cgroup_mutex */
> -static struct move_charge_struct {
> - spinlock_t lock; /* for from, to */
> - struct mm_struct *mm;
> - struct mem_cgroup *from;
> - struct mem_cgroup *to;
> - unsigned long flags;
> - unsigned long precharge;
> - unsigned long moved_charge;
> - unsigned long moved_swap;
> - struct task_struct *moving_task; /* a task moving charges */
> - wait_queue_head_t waitq; /* a waitq for other context */
> -} mc = {
> - .lock = __SPIN_LOCK_UNLOCKED(mc.lock),
> - .waitq = __WAIT_QUEUE_HEAD_INITIALIZER(mc.waitq),
> -};
> -
> /* for OOM */
> struct mem_cgroup_eventfd_list {
> struct list_head list;
> @@ -426,51 +401,6 @@ unsigned long memcg1_soft_limit_reclaim(pg_data_t *pgdat, int order,
> return nr_reclaimed;
> }
>
> -/*
> - * A routine for checking "mem" is under move_account() or not.
> - *
> - * Checking a cgroup is mc.from or mc.to or under hierarchy of
> - * moving cgroups. This is for waiting at high-memory pressure
> - * caused by "move".
> - */
> -static bool mem_cgroup_under_move(struct mem_cgroup *memcg)
> -{
> - struct mem_cgroup *from;
> - struct mem_cgroup *to;
> - bool ret = false;
> - /*
> - * Unlike task_move routines, we access mc.to, mc.from not under
> - * mutual exclusion by cgroup_mutex. Here, we take spinlock instead.
> - */
> - spin_lock(&mc.lock);
> - from = mc.from;
> - to = mc.to;
> - if (!from)
> - goto unlock;
> -
> - ret = mem_cgroup_is_descendant(from, memcg) ||
> - mem_cgroup_is_descendant(to, memcg);
> -unlock:
> - spin_unlock(&mc.lock);
> - return ret;
> -}
> -
> -bool memcg1_wait_acct_move(struct mem_cgroup *memcg)
> -{
> - if (mc.moving_task && current != mc.moving_task) {
> - if (mem_cgroup_under_move(memcg)) {
> - DEFINE_WAIT(wait);
> - prepare_to_wait(&mc.waitq, &wait, TASK_INTERRUPTIBLE);
> - /* moving charge context might have finished. */
> - if (mc.moving_task)
> - schedule();
> - finish_wait(&mc.waitq, &wait);
> - return true;
> - }
> - }
> - return false;
> -}
> -
> /**
> * folio_memcg_lock - Bind a folio to its memcg.
> * @folio: The folio.
> @@ -552,44 +482,6 @@ void folio_memcg_unlock(struct folio *folio)
> __folio_memcg_unlock(folio_memcg(folio));
> }
>
> -#ifdef CONFIG_SWAP
> -/**
> - * mem_cgroup_move_swap_account - move swap charge and swap_cgroup's record.
> - * @entry: swap entry to be moved
> - * @from: mem_cgroup which the entry is moved from
> - * @to: mem_cgroup which the entry is moved to
> - *
> - * It succeeds only when the swap_cgroup's record for this entry is the same
> - * as the mem_cgroup's id of @from.
> - *
> - * Returns 0 on success, -EINVAL on failure.
> - *
> - * The caller must have charged to @to, IOW, called page_counter_charge() about
> - * both res and memsw, and called css_get().
> - */
> -static int mem_cgroup_move_swap_account(swp_entry_t entry,
> - struct mem_cgroup *from, struct mem_cgroup *to)
> -{
> - unsigned short old_id, new_id;
> -
> - old_id = mem_cgroup_id(from);
> - new_id = mem_cgroup_id(to);
> -
> - if (swap_cgroup_cmpxchg(entry, old_id, new_id) == old_id) {
> - mod_memcg_state(from, MEMCG_SWAP, -1);
> - mod_memcg_state(to, MEMCG_SWAP, 1);
> - return 0;
> - }
> - return -EINVAL;
> -}
> -#else
> -static inline int mem_cgroup_move_swap_account(swp_entry_t entry,
> - struct mem_cgroup *from, struct mem_cgroup *to)
> -{
> - return -EINVAL;
> -}
> -#endif
> -
> static u64 mem_cgroup_move_charge_read(struct cgroup_subsys_state *css,
> struct cftype *cft)
> {
> @@ -600,8 +492,6 @@ static u64 mem_cgroup_move_charge_read(struct cgroup_subsys_state *css,
> static int mem_cgroup_move_charge_write(struct cgroup_subsys_state *css,
> struct cftype *cft, u64 val)
> {
> - struct mem_cgroup *memcg = mem_cgroup_from_css(css);
> -
> pr_warn_once("Cgroup memory moving (move_charge_at_immigrate) is deprecated. "
> "Please report your usecase to linux-mm@kvack.org if you "
> "depend on this functionality.\n");
> @@ -616,760 +506,6 @@ static int mem_cgroup_move_charge_write(struct cgroup_subsys_state *css,
> }
> #endif
>
> -#ifdef CONFIG_MMU
> -/* Handlers for move charge at task migration. */
> -static int mem_cgroup_do_precharge(unsigned long count)
> -{
> - int ret;
> -
> - /* Try a single bulk charge without reclaim first, kswapd may wake */
> - ret = try_charge(mc.to, GFP_KERNEL & ~__GFP_DIRECT_RECLAIM, count);
> - if (!ret) {
> - mc.precharge += count;
> - return ret;
> - }
> -
> - /* Try charges one by one with reclaim, but do not retry */
> - while (count--) {
> - ret = try_charge(mc.to, GFP_KERNEL | __GFP_NORETRY, 1);
> - if (ret)
> - return ret;
> - mc.precharge++;
> - cond_resched();
> - }
> - return 0;
> -}
> -
> -union mc_target {
> - struct folio *folio;
> - swp_entry_t ent;
> -};
> -
> -enum mc_target_type {
> - MC_TARGET_NONE = 0,
> - MC_TARGET_PAGE,
> - MC_TARGET_SWAP,
> - MC_TARGET_DEVICE,
> -};
> -
> -static struct page *mc_handle_present_pte(struct vm_area_struct *vma,
> - unsigned long addr, pte_t ptent)
> -{
> - struct page *page = vm_normal_page(vma, addr, ptent);
> -
> - if (!page)
> - return NULL;
> - if (PageAnon(page)) {
> - if (!(mc.flags & MOVE_ANON))
> - return NULL;
> - } else {
> - if (!(mc.flags & MOVE_FILE))
> - return NULL;
> - }
> - get_page(page);
> -
> - return page;
> -}
> -
> -#if defined(CONFIG_SWAP) || defined(CONFIG_DEVICE_PRIVATE)
> -static struct page *mc_handle_swap_pte(struct vm_area_struct *vma,
> - pte_t ptent, swp_entry_t *entry)
> -{
> - struct page *page = NULL;
> - swp_entry_t ent = pte_to_swp_entry(ptent);
> -
> - if (!(mc.flags & MOVE_ANON))
> - return NULL;
> -
> - /*
> - * Handle device private pages that are not accessible by the CPU, but
> - * stored as special swap entries in the page table.
> - */
> - if (is_device_private_entry(ent)) {
> - page = pfn_swap_entry_to_page(ent);
> - if (!get_page_unless_zero(page))
> - return NULL;
> - return page;
> - }
> -
> - if (non_swap_entry(ent))
> - return NULL;
> -
> - /*
> - * Because swap_cache_get_folio() updates some statistics counter,
> - * we call find_get_page() with swapper_space directly.
> - */
> - page = find_get_page(swap_address_space(ent), swap_cache_index(ent));
> - entry->val = ent.val;
> -
> - return page;
> -}
> -#else
> -static struct page *mc_handle_swap_pte(struct vm_area_struct *vma,
> - pte_t ptent, swp_entry_t *entry)
> -{
> - return NULL;
> -}
> -#endif
> -
> -static struct page *mc_handle_file_pte(struct vm_area_struct *vma,
> - unsigned long addr, pte_t ptent)
> -{
> - unsigned long index;
> - struct folio *folio;
> -
> - if (!vma->vm_file) /* anonymous vma */
> - return NULL;
> - if (!(mc.flags & MOVE_FILE))
> - return NULL;
> -
> - /* folio is moved even if it's not RSS of this task(page-faulted). */
> - /* shmem/tmpfs may report page out on swap: account for that too. */
> - index = linear_page_index(vma, addr);
> - folio = filemap_get_incore_folio(vma->vm_file->f_mapping, index);
> - if (IS_ERR(folio))
> - return NULL;
> - return folio_file_page(folio, index);
> -}
> -
> -static void memcg1_check_events(struct mem_cgroup *memcg, int nid);
> -static void memcg1_charge_statistics(struct mem_cgroup *memcg, int nr_pages);
> -
> -/**
> - * mem_cgroup_move_account - move account of the folio
> - * @folio: The folio.
> - * @compound: charge the page as compound or small page
> - * @from: mem_cgroup which the folio is moved from.
> - * @to: mem_cgroup which the folio is moved to. @from != @to.
> - *
> - * The folio must be locked and not on the LRU.
> - *
> - * This function doesn't do "charge" to new cgroup and doesn't do "uncharge"
> - * from old cgroup.
> - */
> -static int mem_cgroup_move_account(struct folio *folio,
> - bool compound,
> - struct mem_cgroup *from,
> - struct mem_cgroup *to)
> -{
> - struct lruvec *from_vec, *to_vec;
> - struct pglist_data *pgdat;
> - unsigned int nr_pages = compound ? folio_nr_pages(folio) : 1;
> - int nid, ret;
> -
> - VM_BUG_ON(from == to);
> - VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
> - VM_BUG_ON_FOLIO(folio_test_lru(folio), folio);
> - VM_BUG_ON(compound && !folio_test_large(folio));
> -
> - ret = -EINVAL;
> - if (folio_memcg(folio) != from)
> - goto out;
> -
> - pgdat = folio_pgdat(folio);
> - from_vec = mem_cgroup_lruvec(from, pgdat);
> - to_vec = mem_cgroup_lruvec(to, pgdat);
> -
> - folio_memcg_lock(folio);
> -
> - if (folio_test_anon(folio)) {
> - if (folio_mapped(folio)) {
> - __mod_lruvec_state(from_vec, NR_ANON_MAPPED, -nr_pages);
> - __mod_lruvec_state(to_vec, NR_ANON_MAPPED, nr_pages);
> - if (folio_test_pmd_mappable(folio)) {
> - __mod_lruvec_state(from_vec, NR_ANON_THPS,
> - -nr_pages);
> - __mod_lruvec_state(to_vec, NR_ANON_THPS,
> - nr_pages);
> - }
> - }
> - } else {
> - __mod_lruvec_state(from_vec, NR_FILE_PAGES, -nr_pages);
> - __mod_lruvec_state(to_vec, NR_FILE_PAGES, nr_pages);
> -
> - if (folio_test_swapbacked(folio)) {
> - __mod_lruvec_state(from_vec, NR_SHMEM, -nr_pages);
> - __mod_lruvec_state(to_vec, NR_SHMEM, nr_pages);
> - }
> -
> - if (folio_mapped(folio)) {
> - __mod_lruvec_state(from_vec, NR_FILE_MAPPED, -nr_pages);
> - __mod_lruvec_state(to_vec, NR_FILE_MAPPED, nr_pages);
> - }
> -
> - if (folio_test_dirty(folio)) {
> - struct address_space *mapping = folio_mapping(folio);
> -
> - if (mapping_can_writeback(mapping)) {
> - __mod_lruvec_state(from_vec, NR_FILE_DIRTY,
> - -nr_pages);
> - __mod_lruvec_state(to_vec, NR_FILE_DIRTY,
> - nr_pages);
> - }
> - }
> - }
> -
> -#ifdef CONFIG_SWAP
> - if (folio_test_swapcache(folio)) {
> - __mod_lruvec_state(from_vec, NR_SWAPCACHE, -nr_pages);
> - __mod_lruvec_state(to_vec, NR_SWAPCACHE, nr_pages);
> - }
> -#endif
> - if (folio_test_writeback(folio)) {
> - __mod_lruvec_state(from_vec, NR_WRITEBACK, -nr_pages);
> - __mod_lruvec_state(to_vec, NR_WRITEBACK, nr_pages);
> - }
> -
> - /*
> - * All state has been migrated, let's switch to the new memcg.
> - *
> - * It is safe to change page's memcg here because the page
> - * is referenced, charged, isolated, and locked: we can't race
> - * with (un)charging, migration, LRU putback, or anything else
> - * that would rely on a stable page's memory cgroup.
> - *
> - * Note that folio_memcg_lock is a memcg lock, not a page lock,
> - * to save space. As soon as we switch page's memory cgroup to a
> - * new memcg that isn't locked, the above state can change
> - * concurrently again. Make sure we're truly done with it.
> - */
> - smp_mb();
> -
> - css_get(&to->css);
> - css_put(&from->css);
> -
> - folio->memcg_data = (unsigned long)to;
> -
> - __folio_memcg_unlock(from);
> -
> - ret = 0;
> - nid = folio_nid(folio);
> -
> - local_irq_disable();
> - memcg1_charge_statistics(to, nr_pages);
> - memcg1_check_events(to, nid);
> - memcg1_charge_statistics(from, -nr_pages);
> - memcg1_check_events(from, nid);
> - local_irq_enable();
> -out:
> - return ret;
> -}
> -
> -/**
> - * get_mctgt_type - get target type of moving charge
> - * @vma: the vma the pte to be checked belongs
> - * @addr: the address corresponding to the pte to be checked
> - * @ptent: the pte to be checked
> - * @target: the pointer the target page or swap ent will be stored(can be NULL)
> - *
> - * Context: Called with pte lock held.
> - * Return:
> - * * MC_TARGET_NONE - If the pte is not a target for move charge.
> - * * MC_TARGET_PAGE - If the page corresponding to this pte is a target for
> - * move charge. If @target is not NULL, the folio is stored in target->folio
> - * with extra refcnt taken (Caller should release it).
> - * * MC_TARGET_SWAP - If the swap entry corresponding to this pte is a
> - * target for charge migration. If @target is not NULL, the entry is
> - * stored in target->ent.
> - * * MC_TARGET_DEVICE - Like MC_TARGET_PAGE but page is device memory and
> - * thus not on the lru. For now such page is charged like a regular page
> - * would be as it is just special memory taking the place of a regular page.
> - * See Documentations/vm/hmm.txt and include/linux/hmm.h
> - */
> -static enum mc_target_type get_mctgt_type(struct vm_area_struct *vma,
> - unsigned long addr, pte_t ptent, union mc_target *target)
> -{
> - struct page *page = NULL;
> - struct folio *folio;
> - enum mc_target_type ret = MC_TARGET_NONE;
> - swp_entry_t ent = { .val = 0 };
> -
> - if (pte_present(ptent))
> - page = mc_handle_present_pte(vma, addr, ptent);
> - else if (pte_none_mostly(ptent))
> - /*
> - * PTE markers should be treated as a none pte here, separated
> - * from other swap handling below.
> - */
> - page = mc_handle_file_pte(vma, addr, ptent);
> - else if (is_swap_pte(ptent))
> - page = mc_handle_swap_pte(vma, ptent, &ent);
> -
> - if (page)
> - folio = page_folio(page);
> - if (target && page) {
> - if (!folio_trylock(folio)) {
> - folio_put(folio);
> - return ret;
> - }
> - /*
> - * page_mapped() must be stable during the move. This
> - * pte is locked, so if it's present, the page cannot
> - * become unmapped. If it isn't, we have only partial
> - * control over the mapped state: the page lock will
> - * prevent new faults against pagecache and swapcache,
> - * so an unmapped page cannot become mapped. However,
> - * if the page is already mapped elsewhere, it can
> - * unmap, and there is nothing we can do about it.
> - * Alas, skip moving the page in this case.
> - */
> - if (!pte_present(ptent) && page_mapped(page)) {
> - folio_unlock(folio);
> - folio_put(folio);
> - return ret;
> - }
> - }
> -
> - if (!page && !ent.val)
> - return ret;
> - if (page) {
> - /*
> - * Do only loose check w/o serialization.
> - * mem_cgroup_move_account() checks the page is valid or
> - * not under LRU exclusion.
> - */
> - if (folio_memcg(folio) == mc.from) {
> - ret = MC_TARGET_PAGE;
> - if (folio_is_device_private(folio) ||
> - folio_is_device_coherent(folio))
> - ret = MC_TARGET_DEVICE;
> - if (target)
> - target->folio = folio;
> - }
> - if (!ret || !target) {
> - if (target)
> - folio_unlock(folio);
> - folio_put(folio);
> - }
> - }
> - /*
> - * There is a swap entry and a page doesn't exist or isn't charged.
> - * But we cannot move a tail-page in a THP.
> - */
> - if (ent.val && !ret && (!page || !PageTransCompound(page)) &&
> - mem_cgroup_id(mc.from) == lookup_swap_cgroup_id(ent)) {
> - ret = MC_TARGET_SWAP;
> - if (target)
> - target->ent = ent;
> - }
> - return ret;
> -}
> -
> -#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> -/*
> - * We don't consider PMD mapped swapping or file mapped pages because THP does
> - * not support them for now.
> - * Caller should make sure that pmd_trans_huge(pmd) is true.
> - */
> -static enum mc_target_type get_mctgt_type_thp(struct vm_area_struct *vma,
> - unsigned long addr, pmd_t pmd, union mc_target *target)
> -{
> - struct page *page = NULL;
> - struct folio *folio;
> - enum mc_target_type ret = MC_TARGET_NONE;
> -
> - if (unlikely(is_swap_pmd(pmd))) {
> - VM_BUG_ON(thp_migration_supported() &&
> - !is_pmd_migration_entry(pmd));
> - return ret;
> - }
> - page = pmd_page(pmd);
> - VM_BUG_ON_PAGE(!page || !PageHead(page), page);
> - folio = page_folio(page);
> - if (!(mc.flags & MOVE_ANON))
> - return ret;
> - if (folio_memcg(folio) == mc.from) {
> - ret = MC_TARGET_PAGE;
> - if (target) {
> - folio_get(folio);
> - if (!folio_trylock(folio)) {
> - folio_put(folio);
> - return MC_TARGET_NONE;
> - }
> - target->folio = folio;
> - }
> - }
> - return ret;
> -}
> -#else
> -static inline enum mc_target_type get_mctgt_type_thp(struct vm_area_struct *vma,
> - unsigned long addr, pmd_t pmd, union mc_target *target)
> -{
> - return MC_TARGET_NONE;
> -}
> -#endif
> -
> -static int mem_cgroup_count_precharge_pte_range(pmd_t *pmd,
> - unsigned long addr, unsigned long end,
> - struct mm_walk *walk)
> -{
> - struct vm_area_struct *vma = walk->vma;
> - pte_t *pte;
> - spinlock_t *ptl;
> -
> - ptl = pmd_trans_huge_lock(pmd, vma);
> - if (ptl) {
> - /*
> - * Note their can not be MC_TARGET_DEVICE for now as we do not
> - * support transparent huge page with MEMORY_DEVICE_PRIVATE but
> - * this might change.
> - */
> - if (get_mctgt_type_thp(vma, addr, *pmd, NULL) == MC_TARGET_PAGE)
> - mc.precharge += HPAGE_PMD_NR;
> - spin_unlock(ptl);
> - return 0;
> - }
> -
> - pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
> - if (!pte)
> - return 0;
> - for (; addr != end; pte++, addr += PAGE_SIZE)
> - if (get_mctgt_type(vma, addr, ptep_get(pte), NULL))
> - mc.precharge++; /* increment precharge temporarily */
> - pte_unmap_unlock(pte - 1, ptl);
> - cond_resched();
> -
> - return 0;
> -}
> -
> -static const struct mm_walk_ops precharge_walk_ops = {
> - .pmd_entry = mem_cgroup_count_precharge_pte_range,
> - .walk_lock = PGWALK_RDLOCK,
> -};
> -
> -static unsigned long mem_cgroup_count_precharge(struct mm_struct *mm)
> -{
> - unsigned long precharge;
> -
> - mmap_read_lock(mm);
> - walk_page_range(mm, 0, ULONG_MAX, &precharge_walk_ops, NULL);
> - mmap_read_unlock(mm);
> -
> - precharge = mc.precharge;
> - mc.precharge = 0;
> -
> - return precharge;
> -}
> -
> -static int mem_cgroup_precharge_mc(struct mm_struct *mm)
> -{
> - unsigned long precharge = mem_cgroup_count_precharge(mm);
> -
> - VM_BUG_ON(mc.moving_task);
> - mc.moving_task = current;
> - return mem_cgroup_do_precharge(precharge);
> -}
> -
> -/* cancels all extra charges on mc.from and mc.to, and wakes up all waiters. */
> -static void __mem_cgroup_clear_mc(void)
> -{
> - struct mem_cgroup *from = mc.from;
> - struct mem_cgroup *to = mc.to;
> -
> - /* we must uncharge all the leftover precharges from mc.to */
> - if (mc.precharge) {
> - mem_cgroup_cancel_charge(mc.to, mc.precharge);
> - mc.precharge = 0;
> - }
> - /*
> - * we didn't uncharge from mc.from at mem_cgroup_move_account(), so
> - * we must uncharge here.
> - */
> - if (mc.moved_charge) {
> - mem_cgroup_cancel_charge(mc.from, mc.moved_charge);
> - mc.moved_charge = 0;
> - }
> - /* we must fixup refcnts and charges */
> - if (mc.moved_swap) {
> - /* uncharge swap account from the old cgroup */
> - if (!mem_cgroup_is_root(mc.from))
> - page_counter_uncharge(&mc.from->memsw, mc.moved_swap);
> -
> - mem_cgroup_id_put_many(mc.from, mc.moved_swap);
> -
> - /*
> - * we charged both to->memory and to->memsw, so we
> - * should uncharge to->memory.
> - */
> - if (!mem_cgroup_is_root(mc.to))
> - page_counter_uncharge(&mc.to->memory, mc.moved_swap);
> -
> - mc.moved_swap = 0;
> - }
> - memcg1_oom_recover(from);
> - memcg1_oom_recover(to);
> - wake_up_all(&mc.waitq);
> -}
> -
> -static void mem_cgroup_clear_mc(void)
> -{
> - struct mm_struct *mm = mc.mm;
> -
> - /*
> - * we must clear moving_task before waking up waiters at the end of
> - * task migration.
> - */
> - mc.moving_task = NULL;
> - __mem_cgroup_clear_mc();
> - spin_lock(&mc.lock);
> - mc.from = NULL;
> - mc.to = NULL;
> - mc.mm = NULL;
> - spin_unlock(&mc.lock);
> -
> - mmput(mm);
> -}
> -
> -int memcg1_can_attach(struct cgroup_taskset *tset)
> -{
> - struct cgroup_subsys_state *css;
> - struct mem_cgroup *memcg = NULL; /* unneeded init to make gcc happy */
> - struct mem_cgroup *from;
> - struct task_struct *leader, *p;
> - struct mm_struct *mm;
> - unsigned long move_flags;
> - int ret = 0;
> -
> - /* charge immigration isn't supported on the default hierarchy */
> - if (cgroup_subsys_on_dfl(memory_cgrp_subsys))
> - return 0;
> -
> - /*
> - * Multi-process migrations only happen on the default hierarchy
> - * where charge immigration is not used. Perform charge
> - * immigration if @tset contains a leader and whine if there are
> - * multiple.
> - */
> - p = NULL;
> - cgroup_taskset_for_each_leader(leader, css, tset) {
> - WARN_ON_ONCE(p);
> - p = leader;
> - memcg = mem_cgroup_from_css(css);
> - }
> - if (!p)
> - return 0;
> -
> - /*
> - * We are now committed to this value whatever it is. Changes in this
> - * tunable will only affect upcoming migrations, not the current one.
> - * So we need to save it, and keep it going.
> - */
> - move_flags = READ_ONCE(memcg->move_charge_at_immigrate);
> - if (!move_flags)
> - return 0;
> -
> - from = mem_cgroup_from_task(p);
> -
> - VM_BUG_ON(from == memcg);
> -
> - mm = get_task_mm(p);
> - if (!mm)
> - return 0;
> - /* We move charges only when we move a owner of the mm */
> - if (mm->owner == p) {
> - VM_BUG_ON(mc.from);
> - VM_BUG_ON(mc.to);
> - VM_BUG_ON(mc.precharge);
> - VM_BUG_ON(mc.moved_charge);
> - VM_BUG_ON(mc.moved_swap);
> -
> - spin_lock(&mc.lock);
> - mc.mm = mm;
> - mc.from = from;
> - mc.to = memcg;
> - mc.flags = move_flags;
> - spin_unlock(&mc.lock);
> - /* We set mc.moving_task later */
> -
> - ret = mem_cgroup_precharge_mc(mm);
> - if (ret)
> - mem_cgroup_clear_mc();
> - } else {
> - mmput(mm);
> - }
> - return ret;
> -}
> -
> -void memcg1_cancel_attach(struct cgroup_taskset *tset)
> -{
> - if (mc.to)
> - mem_cgroup_clear_mc();
> -}
> -
> -static int mem_cgroup_move_charge_pte_range(pmd_t *pmd,
> - unsigned long addr, unsigned long end,
> - struct mm_walk *walk)
> -{
> - int ret = 0;
> - struct vm_area_struct *vma = walk->vma;
> - pte_t *pte;
> - spinlock_t *ptl;
> - enum mc_target_type target_type;
> - union mc_target target;
> - struct folio *folio;
> -
> - ptl = pmd_trans_huge_lock(pmd, vma);
> - if (ptl) {
> - if (mc.precharge < HPAGE_PMD_NR) {
> - spin_unlock(ptl);
> - return 0;
> - }
> - target_type = get_mctgt_type_thp(vma, addr, *pmd, &target);
> - if (target_type == MC_TARGET_PAGE) {
> - folio = target.folio;
> - if (folio_isolate_lru(folio)) {
> - if (!mem_cgroup_move_account(folio, true,
> - mc.from, mc.to)) {
> - mc.precharge -= HPAGE_PMD_NR;
> - mc.moved_charge += HPAGE_PMD_NR;
> - }
> - folio_putback_lru(folio);
> - }
> - folio_unlock(folio);
> - folio_put(folio);
> - } else if (target_type == MC_TARGET_DEVICE) {
> - folio = target.folio;
> - if (!mem_cgroup_move_account(folio, true,
> - mc.from, mc.to)) {
> - mc.precharge -= HPAGE_PMD_NR;
> - mc.moved_charge += HPAGE_PMD_NR;
> - }
> - folio_unlock(folio);
> - folio_put(folio);
> - }
> - spin_unlock(ptl);
> - return 0;
> - }
> -
> -retry:
> - pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
> - if (!pte)
> - return 0;
> - for (; addr != end; addr += PAGE_SIZE) {
> - pte_t ptent = ptep_get(pte++);
> - bool device = false;
> - swp_entry_t ent;
> -
> - if (!mc.precharge)
> - break;
> -
> - switch (get_mctgt_type(vma, addr, ptent, &target)) {
> - case MC_TARGET_DEVICE:
> - device = true;
> - fallthrough;
> - case MC_TARGET_PAGE:
> - folio = target.folio;
> - /*
> - * We can have a part of the split pmd here. Moving it
> - * can be done but it would be too convoluted so simply
> - * ignore such a partial THP and keep it in original
> - * memcg. There should be somebody mapping the head.
> - */
> - if (folio_test_large(folio))
> - goto put;
> - if (!device && !folio_isolate_lru(folio))
> - goto put;
> - if (!mem_cgroup_move_account(folio, false,
> - mc.from, mc.to)) {
> - mc.precharge--;
> - /* we uncharge from mc.from later. */
> - mc.moved_charge++;
> - }
> - if (!device)
> - folio_putback_lru(folio);
> -put: /* get_mctgt_type() gets & locks the page */
> - folio_unlock(folio);
> - folio_put(folio);
> - break;
> - case MC_TARGET_SWAP:
> - ent = target.ent;
> - if (!mem_cgroup_move_swap_account(ent, mc.from, mc.to)) {
> - mc.precharge--;
> - mem_cgroup_id_get_many(mc.to, 1);
> - /* we fixup other refcnts and charges later. */
> - mc.moved_swap++;
> - }
> - break;
> - default:
> - break;
> - }
> - }
> - pte_unmap_unlock(pte - 1, ptl);
> - cond_resched();
> -
> - if (addr != end) {
> - /*
> - * We have consumed all precharges we got in can_attach().
> - * We try charge one by one, but don't do any additional
> - * charges to mc.to if we have failed in charge once in attach()
> - * phase.
> - */
> - ret = mem_cgroup_do_precharge(1);
> - if (!ret)
> - goto retry;
> - }
> -
> - return ret;
> -}
> -
> -static const struct mm_walk_ops charge_walk_ops = {
> - .pmd_entry = mem_cgroup_move_charge_pte_range,
> - .walk_lock = PGWALK_RDLOCK,
> -};
> -
> -static void mem_cgroup_move_charge(void)
> -{
> - lru_add_drain_all();
> - /*
> - * Signal folio_memcg_lock() to take the memcg's move_lock
> - * while we're moving its pages to another memcg. Then wait
> - * for already started RCU-only updates to finish.
> - */
> - atomic_inc(&mc.from->moving_account);
> - synchronize_rcu();
> -retry:
> - if (unlikely(!mmap_read_trylock(mc.mm))) {
> - /*
> - * Someone who are holding the mmap_lock might be waiting in
> - * waitq. So we cancel all extra charges, wake up all waiters,
> - * and retry. Because we cancel precharges, we might not be able
> - * to move enough charges, but moving charge is a best-effort
> - * feature anyway, so it wouldn't be a big problem.
> - */
> - __mem_cgroup_clear_mc();
> - cond_resched();
> - goto retry;
> - }
> - /*
> - * When we have consumed all precharges and failed in doing
> - * additional charge, the page walk just aborts.
> - */
> - walk_page_range(mc.mm, 0, ULONG_MAX, &charge_walk_ops, NULL);
> - mmap_read_unlock(mc.mm);
> - atomic_dec(&mc.from->moving_account);
> -}
> -
> -void memcg1_move_task(void)
> -{
> - if (mc.to) {
> - mem_cgroup_move_charge();
> - mem_cgroup_clear_mc();
> - }
> -}
> -
> -#else /* !CONFIG_MMU */
> -int memcg1_can_attach(struct cgroup_taskset *tset)
> -{
> - return 0;
> -}
> -void memcg1_cancel_attach(struct cgroup_taskset *tset)
> -{
> -}
> -void memcg1_move_task(void)
> -{
> -}
> -#endif
> -
> static void __mem_cgroup_threshold(struct mem_cgroup *memcg, bool swap)
> {
> struct mem_cgroup_threshold_ary *t;
> diff --git a/mm/memcontrol-v1.h b/mm/memcontrol-v1.h
> index c0672e25bcdb..0e3b82951d91 100644
> --- a/mm/memcontrol-v1.h
> +++ b/mm/memcontrol-v1.h
> @@ -80,12 +80,7 @@ static inline void memcg1_soft_limit_reset(struct mem_cgroup *memcg)
> WRITE_ONCE(memcg->soft_limit, PAGE_COUNTER_MAX);
> }
>
> -bool memcg1_wait_acct_move(struct mem_cgroup *memcg);
> -
> struct cgroup_taskset;
> -int memcg1_can_attach(struct cgroup_taskset *tset);
> -void memcg1_cancel_attach(struct cgroup_taskset *tset);
> -void memcg1_move_task(void);
> void memcg1_css_offline(struct mem_cgroup *memcg);
>
> /* for encoding cft->private value on file */
> @@ -130,7 +125,6 @@ static inline void memcg1_free_events(struct mem_cgroup *memcg) {}
> static inline void memcg1_memcg_init(struct mem_cgroup *memcg) {}
> static inline void memcg1_remove_from_trees(struct mem_cgroup *memcg) {}
> static inline void memcg1_soft_limit_reset(struct mem_cgroup *memcg) {}
> -static inline bool memcg1_wait_acct_move(struct mem_cgroup *memcg) { return false; }
> static inline void memcg1_css_offline(struct mem_cgroup *memcg) {}
>
> static inline bool memcg1_oom_prepare(struct mem_cgroup *memcg, bool *locked) { return true; }
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 5c3a8629ef3e..94279b9c766a 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -2242,12 +2242,6 @@ int try_charge_memcg(struct mem_cgroup *memcg, gfp_t gfp_mask,
> */
> if (nr_reclaimed && nr_pages <= (1 << PAGE_ALLOC_COSTLY_ORDER))
> goto retry;
> - /*
> - * At task move, charge accounts can be doubly counted. So, it's
> - * better to wait until the end of task_move if something is going on.
> - */
> - if (memcg1_wait_acct_move(mem_over_limit))
> - goto retry;
>
> if (nr_retries--)
> goto retry;
> @@ -4439,9 +4433,6 @@ struct cgroup_subsys memory_cgrp_subsys = {
> .exit = mem_cgroup_exit,
> .dfl_cftypes = memory_files,
> #ifdef CONFIG_MEMCG_V1
> - .can_attach = memcg1_can_attach,
> - .cancel_attach = memcg1_cancel_attach,
> - .post_attach = memcg1_move_task,
> .legacy_cftypes = mem_cgroup_legacy_files,
> #endif
> .early_init = 0,
> --
> 2.43.5

--
Michal Hocko
SUSE Labs