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Date: Fri, 19 Mar 2021 12:05:10 +0800
From: Muchun Song <songmuchun@...edance.com>
To: Shakeel Butt <shakeelb@...gle.com>
Cc: Roman Gushchin <guro@...com>, Johannes Weiner <hannes@...xchg.org>,
Michal Hocko <mhocko@...nel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Vladimir Davydov <vdavydov.dev@...il.com>,
LKML <linux-kernel@...r.kernel.org>,
Linux MM <linux-mm@...ck.org>,
Xiongchun duan <duanxiongchun@...edance.com>
Subject: Re: [External] Re: [PATCH v4 4/5] mm: memcontrol: use obj_cgroup APIs
to charge kmem pages
On Fri, Mar 19, 2021 at 11:40 AM Shakeel Butt <shakeelb@...gle.com> wrote:
>
> On Thu, Mar 18, 2021 at 4:08 AM Muchun Song <songmuchun@...edance.com> wrote:
> >
> [...]
> >
> > +static inline struct mem_cgroup *get_obj_cgroup_memcg(struct obj_cgroup *objcg)
>
> I would prefer get_mem_cgroup_from_objcg().
Inspired by obj_cgroup_memcg() which returns the memcg from objcg.
So I introduce get_obj_cgroup_memcg() which obtains a reference of
memcg on the basis of obj_cgroup_memcg().
So that the names are more consistent. Just my thought.
So should I rename it to 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().
Good point. I will do this.
>
> > -
> > 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?
I saw a potential user.
[PATCH v10 0/3] Charge loop device i/o to issuing cgroup
To avoid reintroducing them. So I did 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.
Make sense. Will do.
Thanks for your suggestions.
>
> > + } 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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