From: Muchun Song <songmuchun@bytedance.com> To: Michal Hocko <mhocko@suse.com> Cc: Johannes Weiner <hannes@cmpxchg.org>, Vladimir Davydov <vdavydov.dev@gmail.com>, Andrew Morton <akpm@linux-foundation.org>, Cgroups <cgroups@vger.kernel.org>, Linux Memory Management List <linux-mm@kvack.org>, LKML <linux-kernel@vger.kernel.org> Subject: Re: [External] Re: [PATCH 4/4] mm: memcontrol: fix swap uncharge on cgroup v2 Date: Mon, 15 Feb 2021 18:15:36 +0800 [thread overview] Message-ID: <CAMZfGtVSXG5BRR9R3_+eeoCCWBW87GLVNLPwZCyDUHNeAPrXUw@mail.gmail.com> (raw) In-Reply-To: <YCpDSnLSDoE/FHK5@dhcp22.suse.cz> On Mon, Feb 15, 2021 at 5:47 PM Michal Hocko <mhocko@suse.com> wrote: > > On Sat 13-02-21 01:01:59, Muchun Song wrote: > > The swap charges the actual number of swap entries on cgroup v2. > > If a swap cache page is charged successful, and then we uncharge > > the swap counter. It is wrong on cgroup v2. Because the swap > > entry is not freed. > > Is there any actual problem though? Can you describe the specific > scenario please? Swap cache charge life time is a bit tricky and I have > to confess I have to relearn it every time I need to understand it. The > patch would be much more easier to review if the changelog was much more > specific. I copied the reply to Shakeel here. :-) IIUC, I think that we cannot limit the swap to memory.swap.max on cgroup v2. cd /sys/fs/cgroup/ mkdir test cd test echo 8192 > memory.max echo 4096 > memory.swap.max OK. Now we limit swap to 1 page and memory to 2 pages. Firstly, we allocate 1 page from this memory cgroup and swap this page to swap disk. We can see: memory.current: 0 memory.swap.current: 1 Then we touch this page, we will swap in and charge the swap cache page to the memory counter and uncharge the swap counter. memory.current: 1 memory.swap.current: 0 (but actually we use a swap entry) Then we allocate another 1 page from this memory cgroup. memory.current: 2 memory.swap.current: 0 (but actually we use a swap entry) If we swap those 2 pages to swap disk. We can charge and swap those 2 pages successfully. Right? Maybe I am wrong. > > > Fixes: 2d1c498072de ("mm: memcontrol: make swap tracking an integral part of memory control") > > Signed-off-by: Muchun Song <songmuchun@bytedance.com> > > --- > > mm/memcontrol.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > > index c737c8f05992..be6bc5044150 100644 > > --- a/mm/memcontrol.c > > +++ b/mm/memcontrol.c > > @@ -6753,7 +6753,7 @@ int mem_cgroup_charge(struct page *page, struct mm_struct *mm, gfp_t gfp_mask) > > memcg_check_events(memcg, page); > > local_irq_enable(); > > > > - if (PageSwapCache(page)) { > > + if (!cgroup_subsys_on_dfl(memory_cgrp_subsys) && PageSwapCache(page)) { > > swp_entry_t entry = { .val = page_private(page) }; > > /* > > * The swap entry might not get freed for a long time, > > -- > > 2.11.0 > > -- > Michal Hocko > SUSE Labs
WARNING: multiple messages have this Message-ID (diff)
From: Muchun Song <songmuchun-EC8Uxl6Npydl57MIdRCFDg@public.gmane.org> To: Michal Hocko <mhocko-IBi9RG/b67k@public.gmane.org> Cc: Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>, Vladimir Davydov <vdavydov.dev-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>, Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>, Cgroups <cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, Linux Memory Management List <linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org>, LKML <linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org> Subject: Re: [External] Re: [PATCH 4/4] mm: memcontrol: fix swap uncharge on cgroup v2 Date: Mon, 15 Feb 2021 18:15:36 +0800 [thread overview] Message-ID: <CAMZfGtVSXG5BRR9R3_+eeoCCWBW87GLVNLPwZCyDUHNeAPrXUw@mail.gmail.com> (raw) In-Reply-To: <YCpDSnLSDoE/FHK5-2MMpYkNvuYDjFM9bn6wA6Q@public.gmane.org> On Mon, Feb 15, 2021 at 5:47 PM Michal Hocko <mhocko-IBi9RG/b67k@public.gmane.org> wrote: > > On Sat 13-02-21 01:01:59, Muchun Song wrote: > > The swap charges the actual number of swap entries on cgroup v2. > > If a swap cache page is charged successful, and then we uncharge > > the swap counter. It is wrong on cgroup v2. Because the swap > > entry is not freed. > > Is there any actual problem though? Can you describe the specific > scenario please? Swap cache charge life time is a bit tricky and I have > to confess I have to relearn it every time I need to understand it. The > patch would be much more easier to review if the changelog was much more > specific. I copied the reply to Shakeel here. :-) IIUC, I think that we cannot limit the swap to memory.swap.max on cgroup v2. cd /sys/fs/cgroup/ mkdir test cd test echo 8192 > memory.max echo 4096 > memory.swap.max OK. Now we limit swap to 1 page and memory to 2 pages. Firstly, we allocate 1 page from this memory cgroup and swap this page to swap disk. We can see: memory.current: 0 memory.swap.current: 1 Then we touch this page, we will swap in and charge the swap cache page to the memory counter and uncharge the swap counter. memory.current: 1 memory.swap.current: 0 (but actually we use a swap entry) Then we allocate another 1 page from this memory cgroup. memory.current: 2 memory.swap.current: 0 (but actually we use a swap entry) If we swap those 2 pages to swap disk. We can charge and swap those 2 pages successfully. Right? Maybe I am wrong. > > > Fixes: 2d1c498072de ("mm: memcontrol: make swap tracking an integral part of memory control") > > Signed-off-by: Muchun Song <songmuchun-EC8Uxl6Npydl57MIdRCFDg@public.gmane.org> > > --- > > mm/memcontrol.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > > index c737c8f05992..be6bc5044150 100644 > > --- a/mm/memcontrol.c > > +++ b/mm/memcontrol.c > > @@ -6753,7 +6753,7 @@ int mem_cgroup_charge(struct page *page, struct mm_struct *mm, gfp_t gfp_mask) > > memcg_check_events(memcg, page); > > local_irq_enable(); > > > > - if (PageSwapCache(page)) { > > + if (!cgroup_subsys_on_dfl(memory_cgrp_subsys) && PageSwapCache(page)) { > > swp_entry_t entry = { .val = page_private(page) }; > > /* > > * The swap entry might not get freed for a long time, > > -- > > 2.11.0 > > -- > Michal Hocko > SUSE Labs
next prev parent reply other threads:[~2021-02-15 10:17 UTC|newest] Thread overview: 50+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-02-12 17:01 [PATCH 1/4] mm: memcontrol: remove memcg check from memcg_oom_recover Muchun Song 2021-02-12 17:01 ` Muchun Song 2021-02-12 17:01 ` [PATCH 2/4] mm: memcontrol: add missing memcg_oom_recover() when uncharge slab page Muchun Song 2021-02-12 17:01 ` Muchun Song 2021-02-15 9:37 ` Michal Hocko 2021-02-15 9:37 ` Michal Hocko 2021-02-12 17:01 ` [PATCH 3/4] mm: memcontrol: bail out early when id is zero Muchun Song 2021-02-12 17:01 ` Muchun Song 2021-02-15 9:39 ` Michal Hocko 2021-02-15 9:39 ` Michal Hocko 2021-02-15 10:09 ` [External] " Muchun Song 2021-02-15 10:09 ` Muchun Song 2021-02-15 10:09 ` Muchun Song 2021-02-15 10:27 ` Michal Hocko 2021-02-15 10:27 ` Michal Hocko 2021-02-15 11:34 ` Muchun Song 2021-02-15 11:34 ` Muchun Song 2021-02-15 11:34 ` Muchun Song 2021-02-12 17:01 ` [PATCH 4/4] mm: memcontrol: fix swap uncharge on cgroup v2 Muchun Song 2021-02-12 17:01 ` Muchun Song 2021-02-12 18:56 ` Shakeel Butt 2021-02-12 18:56 ` Shakeel Butt 2021-02-13 6:48 ` [External] " Muchun Song 2021-02-13 6:48 ` Muchun Song 2021-02-16 17:16 ` Shakeel Butt 2021-02-16 17:16 ` Shakeel Butt 2021-02-16 17:16 ` Shakeel Butt 2021-02-15 9:47 ` Michal Hocko 2021-02-15 9:47 ` Michal Hocko 2021-02-15 10:15 ` Muchun Song [this message] 2021-02-15 10:15 ` [External] " Muchun Song 2021-02-15 10:15 ` Muchun Song 2021-02-15 10:24 ` Michal Hocko 2021-02-15 10:24 ` Michal Hocko 2021-02-16 16:59 ` Johannes Weiner 2021-02-16 17:17 ` Shakeel Butt 2021-02-16 17:17 ` Shakeel Butt 2021-02-16 17:17 ` Shakeel Butt 2021-02-16 17:19 ` Michal Hocko 2021-02-16 17:19 ` Michal Hocko 2021-02-16 17:28 ` Johannes Weiner 2021-02-16 17:28 ` Johannes Weiner 2021-02-17 5:15 ` [External] " Muchun Song 2021-02-17 5:15 ` Muchun Song 2021-02-17 5:15 ` Muchun Song 2021-02-17 5:11 ` Muchun Song 2021-02-17 5:11 ` Muchun Song 2021-02-17 5:11 ` Muchun Song 2021-02-15 9:24 ` [PATCH 1/4] mm: memcontrol: remove memcg check from memcg_oom_recover Michal Hocko 2021-02-15 9:24 ` Michal Hocko
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