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SubjectRe: [PATCH 1/2] page_cgroup: Reduce allocation overhead for page_cgroup array for CONFIG_SPARSEMEM
On Mon, 28 Feb 2011 11:09:20 +0100
Michal Hocko <mhocko@suse.cz> wrote:

> Hi Andrew,
> could you consider the patch bellow, please?
> The patch was discussed at https://lkml.org/lkml/2011/2/23/232
> ---
> >From 7e5b1e7043605891dacd9e32f19985bc675292f5 Mon Sep 17 00:00:00 2001
> From: Michal Hocko <mhocko@suse.cz>
> Date: Thu, 24 Feb 2011 11:25:44 +0100
> Subject: [PATCH 1/2] page_cgroup: Reduce allocation overhead for page_cgroup array for CONFIG_SPARSEMEM
>
> 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.
>
> ...
>

> @@ -114,19 +140,9 @@ static int __init_refok init_section_page_cgroup(unsigned long pfn)
> int nid, index;
>
> if (!section->page_cgroup) {
> - 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);
> - }
> + nid = page_to_nid(pfn_to_page(pfn));
> + 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,

This conflicts with
memcg-remove-direct-page_cgroup-to-page-pointer.patch, which did

static int __init_refok init_section_page_cgroup(unsigned long pfn)
{
- struct mem_section *section = __pfn_to_section(pfn);
struct page_cgroup *base, *pc;
+ struct mem_section *section;
unsigned long table_size;
+ unsigned long nr;
int nid, index;

- if (!section->page_cgroup) {
- 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);
- }
- /*
- * The value stored in section->page_cgroup is (base - pfn)
- * and it does not point to the memory block allocated above,
- * causing kmemleak false positives.
- */
- kmemleak_not_leak(base);
+ nr = pfn_to_section_nr(pfn);
+ section = __nr_to_section(nr);
+
+ if (section->page_cgroup)
+ return 0;
+
+ 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);



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