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    SubjectRe: [PATCH v4 4/5] mm: memcontrol: use obj_cgroup APIs to charge kmem pages
    On Thu, Mar 18, 2021 at 4:08 AM Muchun Song <songmuchun@bytedance.com> wrote:
    >
    [...]
    >
    > +static inline struct mem_cgroup *get_obj_cgroup_memcg(struct obj_cgroup *objcg)

    I would prefer get_mem_cgroup_from_objcg().

    > +{
    > + struct mem_cgroup *memcg;
    > +
    > + rcu_read_lock();
    > +retry:
    > + memcg = obj_cgroup_memcg(objcg);
    > + if (unlikely(!css_tryget(&memcg->css)))
    > + goto retry;
    > + rcu_read_unlock();
    > +
    > + return memcg;
    > +}
    > +
    > #ifdef CONFIG_MEMCG_KMEM
    > int memcg_alloc_page_obj_cgroups(struct page *page, struct kmem_cache *s,
    > gfp_t gfp, bool new_page)
    > @@ -3070,15 +3088,8 @@ static int obj_cgroup_charge_pages(struct obj_cgroup *objcg, gfp_t gfp,
    > struct mem_cgroup *memcg;
    > int ret;
    >
    > - rcu_read_lock();
    > -retry:
    > - memcg = obj_cgroup_memcg(objcg);
    > - if (unlikely(!css_tryget(&memcg->css)))
    > - goto retry;
    > - rcu_read_unlock();
    > -
    > + memcg = get_obj_cgroup_memcg(objcg);
    > ret = __memcg_kmem_charge(memcg, gfp, nr_pages);

    Why not manually inline __memcg_kmem_charge() here? This is the only user.

    Similarly manually inline __memcg_kmem_uncharge() into
    obj_cgroup_uncharge_pages() and call obj_cgroup_uncharge_pages() in
    obj_cgroup_release().

    > -
    > css_put(&memcg->css);
    >
    > return ret;
    > @@ -3143,18 +3154,18 @@ static void __memcg_kmem_uncharge(struct mem_cgroup *memcg, unsigned int nr_page
    > */
    > int __memcg_kmem_charge_page(struct page *page, gfp_t gfp, int order)
    > {
    > - struct mem_cgroup *memcg;
    > + struct obj_cgroup *objcg;
    > int ret = 0;
    >
    > - memcg = get_mem_cgroup_from_current();

    This was the only use of get_mem_cgroup_from_current(). Why not remove it?

    > - if (memcg && !mem_cgroup_is_root(memcg)) {
    > - ret = __memcg_kmem_charge(memcg, gfp, 1 << order);
    > + objcg = get_obj_cgroup_from_current();
    > + if (objcg) {
    > + ret = obj_cgroup_charge_pages(objcg, gfp, 1 << order);
    > if (!ret) {
    > - page->memcg_data = (unsigned long)memcg |
    > + page->memcg_data = (unsigned long)objcg |
    > MEMCG_DATA_KMEM;
    > return 0;
    > }
    > - css_put(&memcg->css);
    > + obj_cgroup_put(objcg);
    > }
    > return ret;
    > }
    [...]
    > static void uncharge_page(struct page *page, struct uncharge_gather *ug)
    > {
    > unsigned long nr_pages;
    > + struct mem_cgroup *memcg;
    > + struct obj_cgroup *objcg;
    >
    > VM_BUG_ON_PAGE(PageLRU(page), page);
    >
    > - if (!page_memcg(page))
    > - return;
    > -
    > /*
    > * Nobody should be changing or seriously looking at
    > - * page_memcg(page) at this point, we have fully
    > + * page memcg or objcg at this point, we have fully
    > * exclusive access to the page.
    > */
    > + if (PageMemcgKmem(page)) {
    > + objcg = __page_objcg(page);
    > + memcg = get_obj_cgroup_memcg(objcg);

    Can you add a comment that this get matches the put at the end of the
    function and kmem pages do not hold memcg references anymore.

    > + } else {
    > + memcg = __page_memcg(page);
    > + }
    > +
    > + if (!memcg)
    > + return;
    >
    > - if (ug->memcg != page_memcg(page)) {
    > + if (ug->memcg != memcg) {
    > if (ug->memcg) {
    > uncharge_batch(ug);
    > uncharge_gather_clear(ug);
    > }
    > - ug->memcg = page_memcg(page);
    > + ug->memcg = memcg;
    > ug->dummy_page = page;
    >
    > /* pairs with css_put in uncharge_batch */
    > - css_get(&ug->memcg->css);
    > + css_get(&memcg->css);
    > }
    >
    > nr_pages = compound_nr(page);
    > - ug->nr_pages += nr_pages;
    >
    > - if (PageMemcgKmem(page))
    > + if (PageMemcgKmem(page)) {
    > + ug->nr_memory += nr_pages;
    > ug->nr_kmem += nr_pages;
    > - else
    > +
    > + page->memcg_data = 0;
    > + obj_cgroup_put(objcg);
    > + } else {
    > + /* LRU pages aren't accounted at the root level */
    > + if (!mem_cgroup_is_root(memcg))
    > + ug->nr_memory += nr_pages;
    > ug->pgpgout++;
    >
    > - page->memcg_data = 0;
    > - css_put(&ug->memcg->css);
    > + page->memcg_data = 0;
    > + }
    > +
    > + css_put(&memcg->css);
    > }
    >
    > /**
    > --
    > 2.11.0
    >

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