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Message-ID: <20110228091256.GA4648@tiehlicka.suse.cz>
Date: Mon, 28 Feb 2011 10:12:56 +0100
From: Michal Hocko <mhocko@...e.cz>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc: Dave Hansen <dave@...ux.vnet.ibm.com>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] page_cgroup: Reduce allocation overhead for
page_cgroup array for CONFIG_SPARSEMEM v4
On Mon 28-02-11 09:53:47, KAMEZAWA Hiroyuki wrote:
> On Fri, 25 Feb 2011 10:53:57 +0100
> Michal Hocko <mhocko@...e.cz> wrote:
>
> > On Fri 25-02-11 12:25:22, KAMEZAWA Hiroyuki wrote:
> > > On Thu, 24 Feb 2011 14:40:45 +0100
[...]
> > > The patch itself is fine but please update the description.
> >
> > I have updated the description but kept those parts which describe how
> > the memory is wasted for different configurations. Do you have any tips
> > how it can be improved?
> >
>
> This part was in your description.
> ==
> We can reduce the internal fragmentation either by imeplementing 2
> dimensional array and allocate kmalloc aligned sizes for each entry (as
> suggested in https://lkml.org/lkml/2011/2/23/232) or we can get rid of
> kmalloc altogether and allocate directly from the buddy allocator (use
> alloc_pages_exact) as suggested by Dave Hansen.
> ==
>
> please remove 2 dimentional..... etc. That's just a history.
I just wanted to mention both approaches. OK, I can remove that, of
course.
> > >
> > > But have some comments, below.
> > [...]
> > > > -/* __alloc_bootmem...() is protected by !slab_available() */
> > > > +static void *__init_refok alloc_mcg_table(size_t size, int nid)
> > > > +{
> > > > + void *addr = NULL;
> > > > + if((addr = alloc_pages_exact(size, GFP_KERNEL | __GFP_NOWARN)))
> > > > + return addr;
> > > > +
> > > > + if (node_state(nid, N_HIGH_MEMORY)) {
> > > > + addr = kmalloc_node(size, GFP_KERNEL | __GFP_NOWARN, nid);
> > > > + if (!addr)
> > > > + addr = vmalloc_node(size, nid);
> > > > + } else {
> > > > + addr = kmalloc(size, GFP_KERNEL | __GFP_NOWARN);
> > > > + if (!addr)
> > > > + addr = vmalloc(size);
> > > > + }
> > > > +
> > > > + return addr;
> > > > +}
> > >
> > > What is the case we need to call kmalloc_node() even when alloc_pages_exact() fails ?
> > > vmalloc() may need to be called when the size of chunk is larger than
> > > MAX_ORDER or there is fragmentation.....
> >
> > I kept the original kmalloc with fallback to vmalloc because vmalloc is
> > more scarce resource (especially on i386 where we can have memory
> > hotplug configured as well).
> >
>
> My point is, if alloc_pages_exact() failes because of order of the page,
> kmalloc() will always fail.
You are right. I thought that kmalloc can make a difference due to reclaim
but the reclaim is already triggered by alloc_pages_exact and if it doesn't
succeed there are not big chances to have those pages ready for kmalloc.
> Please remove kmalloc().
OK.
Thanks for the review again and the updated patch is bellow:
Change since v3
- updated changelog - to not mentioned 2dim. solution
- get rid of kmalloc fallback based on Kame's suggestion.
- free_page_cgroup accidentally returned void* (we do not need any return value
there)
Changes since v2
- rename alloc_mcg_table to alloc_page_cgroup
- free__mcg_table renamed to free_page_cgroup
- get VM_BUG_ON(!slab_is_available()) back into the allocation path
---
>From 84a9555741b59cb2a0a67b023e4bd0f92c670ca1 Mon Sep 17 00:00:00 2001
From: Michal Hocko <mhocko@...e.cz>
Date: Thu, 24 Feb 2011 11:25:44 +0100
Subject: [PATCH] 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@...e.cz>
CC: Dave Hansen <dave@...ux.vnet.ibm.com>
CC: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
---
mm/page_cgroup.c | 54 +++++++++++++++++++++++++++++++-----------------------
1 files changed, 31 insertions(+), 23 deletions(-)
diff --git a/mm/page_cgroup.c b/mm/page_cgroup.c
index 5bffada..eae3cd2 100644
--- a/mm/page_cgroup.c
+++ b/mm/page_cgroup.c
@@ -105,7 +105,33 @@ struct page_cgroup *lookup_page_cgroup(struct page *page)
return section->page_cgroup + pfn;
}
-/* __alloc_bootmem...() is protected by !slab_available() */
+static void *__init_refok alloc_page_cgroup(size_t size, int nid)
+{
+ void *addr = NULL;
+ if((addr = alloc_pages_exact(size, GFP_KERNEL | __GFP_NOWARN)))
+ 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 mem_section *section = __pfn_to_section(pfn);
@@ -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,
@@ -170,16 +186,8 @@ 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);
- ms->page_cgroup = NULL;
- }
- }
+ free_page_cgroup(base);
+ ms->page_cgroup = NULL;
}
int __meminit online_page_cgroup(unsigned long start_pfn,
--
1.7.2.3
--
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9
Czech Republic
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