From: Dan Schatzberg <schatzberg.dan@xxxxxxxxx> Subject: mm: charge active memcg when no mm is set set_active_memcg() worked for kernel allocations but was silently ignored for user pages. This patch establishes a precedence order for who gets charged: 1. If there is a memcg associated with the page already, that memcg is charged. This happens during swapin. 2. If an explicit mm is passed, mm->memcg is charged. This happens during page faults, which can be triggered in remote VMs (eg gup). 3. Otherwise consult the current process context. If there is an active_memcg, use that. Otherwise, current->mm->memcg. Previously, if a NULL mm was passed to mem_cgroup_charge (case 3) it would always charge the root cgroup. Now it looks up the active_memcg first (falling back to charging the root cgroup if not set). Link: https://lkml.kernel.org/r/20210610173944.1203706-3-schatzberg.dan@xxxxxxxxx Signed-off-by: Dan Schatzberg <schatzberg.dan@xxxxxxxxx> Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx> Acked-by: Tejun Heo <tj@xxxxxxxxxx> Acked-by: Chris Down <chris@xxxxxxxxxxxxxx> Acked-by: Jens Axboe <axboe@xxxxxxxxx> Reviewed-by: Shakeel Butt <shakeelb@xxxxxxxxxx> Reviewed-by: Michal Koutný <mkoutny@xxxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxx> Cc: Ming Lei <ming.lei@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/filemap.c | 2 +- mm/memcontrol.c | 41 +++++++++++++++++++++++++++-------------- mm/shmem.c | 4 ++-- 3 files changed, 30 insertions(+), 17 deletions(-) --- a/mm/filemap.c~mm-charge-active-memcg-when-no-mm-is-set +++ a/mm/filemap.c @@ -872,7 +872,7 @@ noinline int __add_to_page_cache_locked( page->index = offset; if (!huge) { - error = mem_cgroup_charge(page, current->mm, gfp); + error = mem_cgroup_charge(page, NULL, gfp); if (error) goto error; charged = true; --- a/mm/memcontrol.c~mm-charge-active-memcg-when-no-mm-is-set +++ a/mm/memcontrol.c @@ -897,13 +897,24 @@ struct mem_cgroup *mem_cgroup_from_task( } EXPORT_SYMBOL(mem_cgroup_from_task); +static __always_inline struct mem_cgroup *active_memcg(void) +{ + if (in_interrupt()) + return this_cpu_read(int_active_memcg); + else + return current->active_memcg; +} + /** * get_mem_cgroup_from_mm: Obtain a reference on given mm_struct's memcg. * @mm: mm from which memcg should be extracted. It can be NULL. * - * Obtain a reference on mm->memcg and returns it if successful. Otherwise - * root_mem_cgroup is returned. However if mem_cgroup is disabled, NULL is - * returned. + * Obtain a reference on mm->memcg and returns it if successful. If mm + * is NULL, then the memcg is chosen as follows: + * 1) The active memcg, if set. + * 2) current->mm->memcg, if available + * 3) root memcg + * If mem_cgroup is disabled, NULL is returned. */ struct mem_cgroup *get_mem_cgroup_from_mm(struct mm_struct *mm) { @@ -921,8 +932,17 @@ struct mem_cgroup *get_mem_cgroup_from_m * counting is disabled on the root level in the * cgroup core. See CSS_NO_REF. */ - if (unlikely(!mm)) - return root_mem_cgroup; + if (unlikely(!mm)) { + memcg = active_memcg(); + if (unlikely(memcg)) { + /* remote memcg must hold a ref */ + css_get(&memcg->css); + return memcg; + } + mm = current->mm; + if (unlikely(!mm)) + return root_mem_cgroup; + } rcu_read_lock(); do { @@ -935,14 +955,6 @@ struct mem_cgroup *get_mem_cgroup_from_m } EXPORT_SYMBOL(get_mem_cgroup_from_mm); -static __always_inline struct mem_cgroup *active_memcg(void) -{ - if (in_interrupt()) - return this_cpu_read(int_active_memcg); - else - return current->active_memcg; -} - static __always_inline bool memcg_kmem_bypass(void) { /* Allow remote memcg charging from any context. */ @@ -6711,7 +6723,8 @@ out: * @gfp_mask: reclaim mode * * Try to charge @page to the memcg that @mm belongs to, reclaiming - * pages according to @gfp_mask if necessary. + * pages according to @gfp_mask if necessary. if @mm is NULL, try to + * charge to the active memcg. * * Do not use this for pages allocated for swapin. * --- a/mm/shmem.c~mm-charge-active-memcg-when-no-mm-is-set +++ a/mm/shmem.c @@ -1695,7 +1695,7 @@ static int shmem_swapin_page(struct inod { struct address_space *mapping = inode->i_mapping; struct shmem_inode_info *info = SHMEM_I(inode); - struct mm_struct *charge_mm = vma ? vma->vm_mm : current->mm; + struct mm_struct *charge_mm = vma ? vma->vm_mm : NULL; struct swap_info_struct *si; struct page *page = NULL; swp_entry_t swap; @@ -1828,7 +1828,7 @@ repeat: } sbinfo = SHMEM_SB(inode->i_sb); - charge_mm = vma ? vma->vm_mm : current->mm; + charge_mm = vma ? vma->vm_mm : NULL; page = pagecache_get_page(mapping, index, FGP_ENTRY | FGP_HEAD | FGP_LOCK, 0); _
