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d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=/OcK8vS7qwP+2MUiwggUAsGSyQgPJ6vX74pEaK+mCpA=; b=iSR+R414veMGWkicloAsPLwO/Zg4zVMC6sn3xExPiHNkboqvydCvyY1KgC1HQfU27y VCayBg4W1TKyeeftvXrELoeYpaR3SQdAlzJJfFA7uWaqOpVoMve9UwZUUwjwWns7Ey1k LVQkxFJbiaF5SKQtutejBYJbpH5KYKwpLjr5TIQpKixDXMbxb3D+h4qJi37doXedYlYP p6M0hjZCP6PksqExt8jzAj9P4vNpC2gmxH+bd88gj90yS6yLhtSVINUXrx4ICGFfUtus VguYd5gacgtNXc4sbH8q9sVJgemsJdJsxWXfxWWrM0gUnAptJz26L2GSQJ+m38anzTsa Ub3w== X-Gm-Message-State: AOAM530Gwm7AlS2SgW15PHvXnmEv9ZjeWYEt4naVQOXmhtw5vANwufD7 3LHeygGJ7EG2HqktXZLdgy+FOFltind5Jx/F1fdjyOI+VHs= X-Google-Smtp-Source: ABdhPJxcad+TUU7WOPJC9TQcbIdDavzSM9nTnUW8s0epJhwrmsMVdl0Df6mTIo+ZUlYJFp8YDhhALLMeRKwxtRWPXUE= X-Received: by 2002:ac2:50d8:: with SMTP id h24mr1997878lfm.449.1605634984523; Tue, 17 Nov 2020 09:43:04 -0800 (PST) MIME-Version: 1.0 References: <20201110195753.530157-1-guro@fb.com> <20201110195753.530157-2-guro@fb.com> <20201112162303.GB873621@cmpxchg.org> <20201113001926.GA2934489@carbon.dhcp.thefacebook.com> In-Reply-To: <20201113001926.GA2934489@carbon.dhcp.thefacebook.com> From: Shakeel Butt Date: Tue, 17 Nov 2020 09:42:53 -0800 Message-ID: Subject: Re: [PATCH 2/2] mm: memcg/slab: pre-allocate obj_cgroups for slab caches with SLAB_ACCOUNT To: Roman Gushchin Cc: Johannes Weiner , Andrew Morton , Linux MM , Michal Hocko , Christoph Lameter , LKML , Kernel Team 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 Thu, Nov 12, 2020 at 4:19 PM Roman Gushchin wrote: > [snip] > > From 8b28d91475d54c552e503e66f169e1e00475c856 Mon Sep 17 00:00:00 2001 > From: Roman Gushchin > Date: Wed, 16 Sep 2020 15:43:48 -0700 > Subject: [PATCH v2 2/2] mm: memcg/slab: pre-allocate obj_cgroups for slab > caches with SLAB_ACCOUNT > > In general it's unknown in advance if a slab page will contain > accounted objects or not. In order to avoid memory waste, an > obj_cgroup vector is allocated dynamically when a need to account > of a new object arises. Such approach is memory efficient, but > requires an expensive cmpxchg() to set up the memcg/objcgs pointer, > because an allocation can race with a different allocation on another > cpu. > > But in some common cases it's known for sure that a slab page will > contain accounted objects: if the page belongs to a slab cache with a > SLAB_ACCOUNT flag set. It includes such popular objects like > vm_area_struct, anon_vma, task_struct, etc. > > In such cases we can pre-allocate the objcgs vector and simple assign > it to the page without any atomic operations, because at this early > stage the page is not visible to anyone else. > > v2: inline set_page_objcgs() and add some comments, by Johannes > > Signed-off-by: Roman Gushchin [snip] > > static __always_inline void account_slab_page(struct page *page, int order, > - struct kmem_cache *s) > + struct kmem_cache *s, > + gfp_t gfp) > { > + if (memcg_kmem_enabled() && (s->flags & SLAB_ACCOUNT)) > + memcg_alloc_page_obj_cgroups(page, s, gfp, true); > + I was wondering why not add (gfp & __GFP_ACCOUNT) check as well but it seems like for that some additional plumbing is required. Anyways: Reviewed-by: Shakeel Butt