On Mon 28-02-11 09:53:47, KAMEZAWA Hiroyuki wrote: > On Fri, 25 Feb 2011 10:53:57 +0100 > Michal Hocko <mhocko@xxxxxxx> 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@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 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@xxxxxxx> CC: Dave Hansen <dave@xxxxxxxxxxxxxxxxxx> CC: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> --- 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. 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