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Mon, 01 Feb 2021 09:09:57 -0800 (PST) MIME-Version: 1.0 References: <20210127233345.339910-1-shy828301@gmail.com> <20210127233345.339910-8-shy828301@gmail.com> <6b0638ba-2513-67f5-8ef1-9e60a7d9ded6@suse.cz> <0ce8b6e4-5abb-3edb-8423-f6c222420a89@suse.cz> In-Reply-To: <0ce8b6e4-5abb-3edb-8423-f6c222420a89@suse.cz> From: Yang Shi Date: Mon, 1 Feb 2021 09:09:45 -0800 Message-ID: Subject: Re: [v5 PATCH 07/11] mm: vmscan: add per memcg shrinker nr_deferred To: Vlastimil Babka Cc: Roman Gushchin , Kirill Tkhai , Shakeel Butt , Dave Chinner , Johannes Weiner , Michal Hocko , Andrew Morton , Linux MM , Linux FS-devel Mailing List , Linux Kernel Mailing List Content-Type: text/plain; charset="UTF-8" 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 Mon, Feb 1, 2021 at 7:17 AM Vlastimil Babka wrote: > > On 1/29/21 7:04 PM, Yang Shi wrote: > > >> > > @@ -209,9 +214,15 @@ static int expand_one_shrinker_info(struct mem_cgroup *memcg, > >> > > if (!new) > >> > > return -ENOMEM; > >> > > > >> > > - /* Set all old bits, clear all new bits */ > >> > > - memset(new->map, (int)0xff, old_size); > >> > > - memset((void *)new->map + old_size, 0, size - old_size); > >> > > + new->map = (unsigned long *)(new + 1); > >> > > + new->nr_deferred = (void *)new->map + m_size; > >> > > >> > This better be aligned to sizeof(atomic_long_t). Can we be sure about that? > >> > >> Good point. No, if unsigned long is 32 bit on some 64 bit machines. > > > > I think we could just change map to "u64" and guarantee struct > > shrinker_info is aligned to 64 bit. > > What about changing to order, nr_deferred before map? Then the atomics are at > the beginning of allocated area, thus aligned. Yes, it works too. The rcu_head is guaranteed to have aligned at sizeof(void *). Will fix in v6.