Re: [PATCH v3 2/3] mm: Charge active memcg when no mm is set
From: Shakeel Butt <hidden>
Date: 2020-02-20 18:14:59
Also in:
cgroups, linux-mm, lkml
On Thu, Feb 20, 2020 at 8:52 AM Dan Schatzberg [off-list ref] wrote:
memalloc_use_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 it has configured a current->active_memcg, use that.
What if css_tryget_online(current->active_memcg) in get_mem_cgroup_from_current() fails? Do we want to change this to css_tryget() and even if that fails should we fallback to root_mem_cgroup or current->mm->memcg?
quoted hunk ↗ jump to hunk
Otherwise, current->mm->memcg. Previously, if a NULL mm was passed to mem_cgroup_try_charge (case 3) it would always charge the root cgroup. Now it looks up the current active_memcg first (falling back to charging the root cgroup if not set). Signed-off-by: Dan Schatzberg <redacted> Acked-by: Johannes Weiner <hannes@cmpxchg.org> Acked-by: Tejun Heo <tj@kernel.org> --- mm/memcontrol.c | 11 ++++++++--- mm/shmem.c | 2 +- 2 files changed, 9 insertions(+), 4 deletions(-)diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 6f6dc8712e39..b174aff4f069 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c@@ -6317,7 +6317,8 @@ enum mem_cgroup_protection mem_cgroup_protected(struct mem_cgroup *root, * @compound: charge the page as compound or small page * * 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. * * Returns 0 on success, with *@memcgp pointing to the charged memcg. * Otherwise, an error code is returned.@@ -6361,8 +6362,12 @@ int mem_cgroup_try_charge(struct page *page, struct mm_struct *mm, } } - if (!memcg) - memcg = get_mem_cgroup_from_mm(mm); + if (!memcg) { + if (!mm) + memcg = get_mem_cgroup_from_current(); + else + memcg = get_mem_cgroup_from_mm(mm); + } ret = try_charge(memcg, gfp_mask, nr_pages);diff --git a/mm/shmem.c b/mm/shmem.c index c8f7540ef048..7c7f5acf89d6 100644 --- a/mm/shmem.c +++ b/mm/shmem.c@@ -1766,7 +1766,7 @@ static int shmem_getpage_gfp(struct inode *inode, pgoff_t index, } sbinfo = SHMEM_SB(inode->i_sb); - charge_mm = vma ? vma->vm_mm : current->mm; + charge_mm = vma ? vma->vm_mm : NULL; page = find_lock_entry(mapping, index); if (xa_is_value(page)) { --2.17.1