On Thu, 24 Feb 2011 14:40:45 +0100 Michal Hocko <mhocko@xxxxxxx> wrote: > Here is the second version of the patch. I have used alloc_pages_exact > instead of the complex double array approach. > > I still fallback to kmalloc/vmalloc because hotplug can happen quite > some time after boot and we can end up not having enough continuous > pages at that time. > > I am also thinking whether it would make sense to introduce > alloc_pages_exact_node function which would allocate pages from the > given node. > > Any thoughts? The patch itself is fine but please update the description. But have some comments, below. > --- > From e8909bbd1d759de274a6ed7812530e576ad8bc44 Mon Sep 17 00:00:00 2001 > From: Michal Hocko <mhocko@xxxxxxx> > 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 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. > > The later solution is much simpler and the internal fragmentation is > comparable (~1 page per section). > > We still need a fallback to kmalloc/vmalloc because we have no > guarantees that we will have a continuous memory of that size (order-10) > later on the hotplug events. > > Signed-off-by: Michal Hocko <mhocko@xxxxxxx> > --- > mm/page_cgroup.c | 62 ++++++++++++++++++++++++++++++++++-------------------- > 1 files changed, 39 insertions(+), 23 deletions(-) > > diff --git a/mm/page_cgroup.c b/mm/page_cgroup.c > index 5bffada..eaae7de 100644 > --- a/mm/page_cgroup.c > +++ b/mm/page_cgroup.c > @@ -105,7 +105,41 @@ 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_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..... And the function name, alloc_mcg_table(), I don't like it because this is an allocation for page_cgroup. How about alloc_page_cgroup() simply ? Thanks, -Kame -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>