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Fri, 09 Jul 2021 19:41:09 -0700 (PDT) MIME-Version: 1.0 References: <20210710003626.3549282-1-surenb@google.com> In-Reply-To: From: Suren Baghdasaryan Date: Fri, 9 Jul 2021 19:40:58 -0700 Message-ID: Subject: Re: [PATCH v3 1/3] mm, memcg: add mem_cgroup_disabled checks in vmpressure and swap-related functions To: Miaohe Lin Cc: Johannes Weiner , Michal Hocko , vdavydov.dev@gmail.com, Andrew Morton , Shakeel Butt , Roman Gushchin , songmuchun@bytedance.com, Yang Shi , alexs@kernel.org, richard.weiyang@gmail.com, Vlastimil Babka , Jens Axboe , Joonsoo Kim , David Hildenbrand , Matthew Wilcox , apopple@nvidia.com, Minchan Kim , LKML , cgroups mailinglist , linux-mm , kernel-team , Tejun Heo Content-Type: text/plain; charset="UTF-8" Authentication-Results: imf19.hostedemail.com; dkim=pass header.d=google.com header.s=20161025 header.b=fqGFrgFB; spf=pass (imf19.hostedemail.com: domain of surenb@google.com designates 209.85.219.171 as permitted sender) smtp.mailfrom=surenb@google.com; dmarc=pass (policy=reject) header.from=google.com X-Rspamd-Server: rspam02 X-Stat-Signature: rh3obnhegtsq96ad5wir5ywf3rj6efq9 X-Rspamd-Queue-Id: E4A6DB00018C X-HE-Tag: 1625884870-837306 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Fri, Jul 9, 2021 at 6:52 PM Miaohe Lin wrote: > > On 2021/7/10 8:36, Suren Baghdasaryan wrote: > > Add mem_cgroup_disabled check in vmpressure, mem_cgroup_uncharge_swap and > > cgroup_throttle_swaprate functions. This minimizes the memcg overhead in > > the pagefault and exit_mmap paths when memcgs are disabled using > > cgroup_disable=memory command-line option. > > This change results in ~2.1% overhead reduction when running PFT test > > comparing {CONFIG_MEMCG=n, CONFIG_MEMCG_SWAP=n} against {CONFIG_MEMCG=y, > > CONFIG_MEMCG_SWAP=y, cgroup_disable=memory} configuration on an 8-core > > ARM64 Android device. > > > > Signed-off-by: Suren Baghdasaryan > > Reviewed-by: Shakeel Butt > > Acked-by: Johannes Weiner > > --- > > mm/memcontrol.c | 3 +++ > > mm/swapfile.c | 3 +++ > > mm/vmpressure.c | 7 ++++++- > > 3 files changed, 12 insertions(+), 1 deletion(-) > > > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > > index ae1f5d0cb581..a228cd51c4bd 100644 > > --- a/mm/memcontrol.c > > +++ b/mm/memcontrol.c > > @@ -7305,6 +7305,9 @@ void mem_cgroup_uncharge_swap(swp_entry_t entry, unsigned int nr_pages) > > struct mem_cgroup *memcg; > > unsigned short id; > > > > + if (mem_cgroup_disabled()) > > + return; > > + > > id = swap_cgroup_record(entry, 0, nr_pages); > > rcu_read_lock(); > > memcg = mem_cgroup_from_id(id); > > diff --git a/mm/swapfile.c b/mm/swapfile.c > > index 1e07d1c776f2..707fa0481bb4 100644 > > --- a/mm/swapfile.c > > +++ b/mm/swapfile.c > > @@ -3778,6 +3778,9 @@ void cgroup_throttle_swaprate(struct page *page, gfp_t gfp_mask) > > struct swap_info_struct *si, *next; > > int nid = page_to_nid(page); > > > > + if (mem_cgroup_disabled()) > > + return; > > + > > Many thanks for your patch. But I'am somewhat confused about this change. > IMO, cgroup_throttle_swaprate() is only related to blk_cgroup and it seems > it's irrelevant to mem_cgroup. Could you please have a explanation for me? cgroup_throttle_swaprate() is a NoOp when CONFIG_MEMCG=n (see: https://elixir.bootlin.com/linux/latest/source/include/linux/swap.h#L699), therefore I assume we can safely skip it when memcgs are disabled via "cgroup_disable=memory". From perf results I also see no hits on this function when CONFIG_MEMCG=n. However, looking into the code, I'm not sure why it should depend on CONFIG_MEMCG. But it's Friday night and I might be missing some details here... > > Thanks! > > > if (!(gfp_mask & __GFP_IO)) > > return; > > > > diff --git a/mm/vmpressure.c b/mm/vmpressure.c > > index d69019fc3789..9b172561fded 100644 > > --- a/mm/vmpressure.c > > +++ b/mm/vmpressure.c > > @@ -240,7 +240,12 @@ static void vmpressure_work_fn(struct work_struct *work) > > void vmpressure(gfp_t gfp, struct mem_cgroup *memcg, bool tree, > > unsigned long scanned, unsigned long reclaimed) > > { > > - struct vmpressure *vmpr = memcg_to_vmpressure(memcg); > > + struct vmpressure *vmpr; > > + > > + if (mem_cgroup_disabled()) > > + return; > > + > > + vmpr = memcg_to_vmpressure(memcg); > > > > /* > > * Here we only want to account pressure that userland is able to > > >