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SubjectRe: [PATCH 1/2] page_cgroup: Reduce allocation overhead for page_cgroup array for CONFIG_SPARSEMEM
On Tue 01-03-11 16:05:50, Andrew Morton wrote:
> 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
[...]
> This conflicts with
> memcg-remove-direct-page_cgroup-to-page-pointer.patch, which did

I have based my patch on top of the current Linus tree. Sorry about
that. Here is the patch rebased on top of the mmotm (2011-02-10-16-26).
The patch passes also checkpatch now.
---
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.

Signed-off-by: Michal Hocko <mhocko@suse.cz>
CC: Dave Hansen <dave@linux.vnet.ibm.com>
CC: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

Index: linux-2.6.38-rc4/mm/page_cgroup.c
===================================================================
--- linux-2.6.38-rc4.orig/mm/page_cgroup.c 2011-03-02 10:42:32.000000000 +0100
+++ linux-2.6.38-rc4/mm/page_cgroup.c 2011-03-02 10:59:41.000000000 +0100
@@ -130,7 +130,36 @@ struct page *lookup_cgroup_page(struct p
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;
+}
+
+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);
+ }
+ }
+}
+
static int __init_refok init_section_page_cgroup(unsigned long pfn)
{
struct page_cgroup *base, *pc;
@@ -147,17 +176,8 @@ static int __init_refok init_section_pag

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,
@@ -189,16 +209,8 @@ void __free_page_cgroup(unsigned long pf
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);
- ms->page_cgroup = NULL;
- }
- }
+ free_page_cgroup(base);
+ ms->page_cgroup = NULL;
}

int __meminit online_page_cgroup(unsigned long start_pfn,
--
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9
Czech Republic

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