page_cgroup: reduce allocation overhead for page_cgroup array for CONFIG_SPARSEMEM (dde79e00) · Commits · 戴 / test

Currently we are allocating a single page_cgroup array per memory section (stored in mem_section->base) when CONFIG_SPARSEMEM is selected. This is correct but memory inefficient solution because the allocated memory (unless we fall back to vmalloc) is not kmalloc friendly: - 32b - 16384 entries (20B per entry) fit into 327680B so the 524288B slab cache is used - 32b with PAE - 131072 entries with 2621440B fit into 4194304B - 64b - 32768 entries (40B per entry) fit into 2097152 cache This is ~37% wasted space per memory section and it sumps up for the whole memory. On a x86_64 machine it is something like 6MB per 1GB of RAM. We can reduce the internal fragmentation by using alloc_pages_exact which allocates PAGE_SIZE aligned blocks so we will get down to <4kB wasted memory per section which is much better. We still need a fallback to vmalloc because we have no guarantees that we will have a continuous memory of that size (order-10) later on during the hotplug events. [hannes@cmpxchg.org: do not define unused free_page_cgroup() without memory hotplug] Signed-off-by:

Michal Hocko <mhocko@suse.cz> Cc: Dave Hansen <dave@linux.vnet.ibm.com> Acked-by:

KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Cc: Balbir Singh <balbir@in.ibm.com> Signed-off-by:

Johannes Weiner <hannes@cmpxchg.org> Signed-off-by:

Andrew Morton <akpm@linux-foundation.org> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

mm/page_cgroup.c

+36 −22

Original line number	Diff line number	Diff line
		@@ -130,7 +130,38 @@ struct page lookup_cgroup_page(struct page_cgroup pc)
		return page;
		}

		/* __alloc_bootmem...() is protected by !slab_available() */
		static void *__init_refok alloc_page_cgroup(size_t size, int nid)
		{
		void *addr = NULL;

		addr = alloc_pages_exact(size, GFP_KERNEL \| __GFP_NOWARN);
		if (addr)
		return addr;

		if (node_state(nid, N_HIGH_MEMORY))
		addr = vmalloc_node(size, nid);
		else
		addr = vmalloc(size);

		return addr;
		}

		#ifdef CONFIG_MEMORY_HOTPLUG
		static void free_page_cgroup(void *addr)
		{
		if (is_vmalloc_addr(addr)) {
		vfree(addr);
		} else {
		struct page *page = virt_to_page(addr);
		if (!PageReserved(page)) { /* Is bootmem ? */
		size_t table_size =
		sizeof(struct page_cgroup) * PAGES_PER_SECTION;
		free_pages_exact(addr, table_size);
		}
		}
		}
		#endif

		static int __init_refok init_section_page_cgroup(unsigned long pfn)
		{
		struct page_cgroup base, pc;
		@@ -147,17 +178,8 @@ static int __init_refok init_section_page_cgroup(unsigned long pfn)

		nid = page_to_nid(pfn_to_page(pfn));
		table_size = sizeof(struct page_cgroup) * PAGES_PER_SECTION;
		VM_BUG_ON(!slab_is_available());
		if (node_state(nid, N_HIGH_MEMORY)) {
		base = kmalloc_node(table_size,
		GFP_KERNEL \| __GFP_NOWARN, nid);
		if (!base)
		base = vmalloc_node(table_size, nid);
		} else {
		base = kmalloc(table_size, GFP_KERNEL \| __GFP_NOWARN);
		if (!base)
		base = vmalloc(table_size);
		}
		base = alloc_page_cgroup(table_size, nid);

		/*
		* The value stored in section->page_cgroup is (base - pfn)
		* and it does not point to the memory block allocated above,
		@@ -189,17 +211,9 @@ void __free_page_cgroup(unsigned long pfn)
		if (!ms \|\| !ms->page_cgroup)
		return;
		base = ms->page_cgroup + pfn;
		if (is_vmalloc_addr(base)) {
		vfree(base);
		ms->page_cgroup = NULL;
		} else {
		struct page *page = virt_to_page(base);
		if (!PageReserved(page)) { /* Is bootmem ? */
		kfree(base);
		free_page_cgroup(base);
		ms->page_cgroup = NULL;
		}
		}
		}

		int __meminit online_page_cgroup(unsigned long start_pfn,
		unsigned long nr_pages,

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