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SubjectRe: [patch 5/5] memcg: remove direct page_cgroup-to-page pointer
On Thu,  3 Feb 2011 15:26:06 +0100
Johannes Weiner <hannes@cmpxchg.org> wrote:

> In struct page_cgroup, we have a full word for flags but only a few
> are reserved. Use the remaining upper bits to encode, depending on
> configuration, the node or the section, to enable page_cgroup-to-page
> lookups without a direct pointer.
>
> This saves a full word for every page in a system with memory cgroups
> enabled.
>
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>

In general,

Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

Thank you. A few questions below.



> ---
> include/linux/page_cgroup.h | 70 +++++++++++++++++++++++++++---------
> kernel/bounds.c | 2 +
> mm/memcontrol.c | 6 ++-
> mm/page_cgroup.c | 85 +++++++++++++++++++++++++------------------
> 4 files changed, 108 insertions(+), 55 deletions(-)
>
> diff --git a/include/linux/page_cgroup.h b/include/linux/page_cgroup.h
> index 6b63679..05d8618 100644
> --- a/include/linux/page_cgroup.h
> +++ b/include/linux/page_cgroup.h
> @@ -1,8 +1,26 @@
> #ifndef __LINUX_PAGE_CGROUP_H
> #define __LINUX_PAGE_CGROUP_H
>
> +enum {
> + /* flags for mem_cgroup */
> + PCG_LOCK, /* Lock for pc->mem_cgroup and following bits. */
> + PCG_CACHE, /* charged as cache */
> + PCG_USED, /* this object is in use. */
> + PCG_MIGRATION, /* under page migration */
> + /* flags for mem_cgroup and file and I/O status */
> + PCG_MOVE_LOCK, /* For race between move_account v.s. following bits */
> + PCG_FILE_MAPPED, /* page is accounted as "mapped" */
> + /* No lock in page_cgroup */
> + PCG_ACCT_LRU, /* page has been accounted for (under lru_lock) */
> + __NR_PCG_FLAGS,
> +};
> +
> +#ifndef __GENERATING_BOUNDS_H
> +#include <generated/bounds.h>
> +
> #ifdef CONFIG_CGROUP_MEM_RES_CTLR
> #include <linux/bit_spinlock.h>
> +
> /*
> * Page Cgroup can be considered as an extended mem_map.
> * A page_cgroup page is associated with every page descriptor. The
> @@ -13,7 +31,6 @@
> struct page_cgroup {
> unsigned long flags;
> struct mem_cgroup *mem_cgroup;
> - struct page *page;
> struct list_head lru; /* per cgroup LRU list */
> };
>
> @@ -32,19 +49,7 @@ static inline void __init page_cgroup_init(void)
> #endif
>
> struct page_cgroup *lookup_page_cgroup(struct page *page);
> -
> -enum {
> - /* flags for mem_cgroup */
> - PCG_LOCK, /* Lock for pc->mem_cgroup and following bits. */
> - PCG_CACHE, /* charged as cache */
> - PCG_USED, /* this object is in use. */
> - PCG_MIGRATION, /* under page migration */
> - /* flags for mem_cgroup and file and I/O status */
> - PCG_MOVE_LOCK, /* For race between move_account v.s. following bits */
> - PCG_FILE_MAPPED, /* page is accounted as "mapped" */
> - /* No lock in page_cgroup */
> - PCG_ACCT_LRU, /* page has been accounted for (under lru_lock) */
> -};
> +struct page *lookup_cgroup_page(struct page_cgroup *pc);
>
> #define TESTPCGFLAG(uname, lname) \
> static inline int PageCgroup##uname(struct page_cgroup *pc) \
> @@ -117,6 +122,34 @@ static inline void move_unlock_page_cgroup(struct page_cgroup *pc,
> local_irq_restore(*flags);
> }
>
> +#ifdef CONFIG_SPARSEMEM
> +#define PCG_ARRAYID_SHIFT SECTIONS_SHIFT
> +#else
> +#define PCG_ARRAYID_SHIFT NODES_SHIFT
> +#endif
> +
> +#if (PCG_ARRAYID_SHIFT > BITS_PER_LONG - NR_PCG_FLAGS)
> +#error Not enough space left in pc->flags to store page_cgroup array IDs
> +#endif
> +
> +/* pc->flags: ARRAY-ID | FLAGS */
> +
> +#define PCG_ARRAYID_MASK ((1UL << PCG_ARRAYID_SHIFT) - 1)
> +
> +#define PCG_ARRAYID_OFFSET (sizeof(unsigned long) * 8 - PCG_ARRAYID_SHIFT)
> +
> +static inline void set_page_cgroup_array_id(struct page_cgroup *pc,
> + unsigned long id)
> +{
> + pc->flags &= ~(PCG_ARRAYID_MASK << PCG_ARRAYID_OFFSET);
> + pc->flags |= (id & PCG_ARRAYID_MASK) << PCG_ARRAYID_OFFSET;
> +}
> +
> +static inline unsigned long page_cgroup_array_id(struct page_cgroup *pc)
> +{
> + return (pc->flags >> PCG_ARRAYID_OFFSET) & PCG_ARRAYID_MASK;
> +}
> +

If a function for looking up a page from a page_cgroup in inline,
I think these function should be static in page_cgroup.c



> #else /* CONFIG_CGROUP_MEM_RES_CTLR */
> struct page_cgroup;
>
> @@ -137,7 +170,7 @@ static inline void __init page_cgroup_init_flatmem(void)
> {
> }
>
> -#endif
> +#endif /* CONFIG_CGROUP_MEM_RES_CTLR */
>
> #include <linux/swap.h>
>
> @@ -173,5 +206,8 @@ static inline void swap_cgroup_swapoff(int type)
> return;
> }
>
> -#endif
> -#endif
> +#endif /* CONFIG_CGROUP_MEM_RES_CTLR_SWAP */
> +
> +#endif /* !__GENERATING_BOUNDS_H */
> +
> +#endif /* __LINUX_PAGE_CGROUP_H */
> diff --git a/kernel/bounds.c b/kernel/bounds.c
> index 98a51f2..0c9b862 100644
> --- a/kernel/bounds.c
> +++ b/kernel/bounds.c
> @@ -9,11 +9,13 @@
> #include <linux/page-flags.h>
> #include <linux/mmzone.h>
> #include <linux/kbuild.h>
> +#include <linux/page_cgroup.h>
>
> void foo(void)
> {
> /* The enum constants to put into include/generated/bounds.h */
> DEFINE(NR_PAGEFLAGS, __NR_PAGEFLAGS);
> DEFINE(MAX_NR_ZONES, __MAX_NR_ZONES);
> + DEFINE(NR_PCG_FLAGS, __NR_PCG_FLAGS);
> /* End of constants */
> }
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 998da06..4e10f46 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1054,7 +1054,8 @@ unsigned long mem_cgroup_isolate_pages(unsigned long nr_to_scan,
> if (unlikely(!PageCgroupUsed(pc)))
> continue;
>
> - page = pc->page;
> + page = lookup_cgroup_page(pc);
> + VM_BUG_ON(pc != lookup_page_cgroup(page));

If you're afraid of corruption in ->flags bit, checking this in page_cgroup.c
is better.


Anyway, seems great.

Thanks,
-Kame

>
> if (unlikely(!PageLRU(page)))
> continue;
> @@ -3296,7 +3297,8 @@ static int mem_cgroup_force_empty_list(struct mem_cgroup *mem,
> }
> spin_unlock_irqrestore(&zone->lru_lock, flags);
>
> - page = pc->page;
> + page = lookup_cgroup_page(pc);
> + VM_BUG_ON(pc != lookup_page_cgroup(page));
>
> ret = mem_cgroup_move_parent(page, pc, mem, GFP_KERNEL);
> if (ret == -ENOMEM)
> diff --git a/mm/page_cgroup.c b/mm/page_cgroup.c
> index 59a3cd4..e5f38e8 100644
> --- a/mm/page_cgroup.c
> +++ b/mm/page_cgroup.c
> @@ -11,12 +11,11 @@
> #include <linux/swapops.h>
> #include <linux/kmemleak.h>
>
> -static void __meminit
> -__init_page_cgroup(struct page_cgroup *pc, unsigned long pfn)
> +static void __meminit init_page_cgroup(struct page_cgroup *pc, unsigned long id)
> {
> pc->flags = 0;
> + set_page_cgroup_array_id(pc, id);
> pc->mem_cgroup = NULL;
> - pc->page = pfn_to_page(pfn);
> INIT_LIST_HEAD(&pc->lru);
> }
> static unsigned long total_usage;
> @@ -43,6 +42,16 @@ struct page_cgroup *lookup_page_cgroup(struct page *page)
> return base + offset;
> }
>
> +struct page *lookup_cgroup_page(struct page_cgroup *pc)
> +{
> + unsigned long pfn;
> + pg_data_t *pgdat;
> +
> + pgdat = NODE_DATA(page_cgroup_array_id(pc));
> + pfn = pc - pgdat->node_page_cgroup + pgdat->node_start_pfn;
> + return pfn_to_page(pfn);
> +}
> +
> static int __init alloc_node_page_cgroup(int nid)
> {
> struct page_cgroup *base, *pc;
> @@ -63,7 +72,7 @@ static int __init alloc_node_page_cgroup(int nid)
> return -ENOMEM;
> for (index = 0; index < nr_pages; index++) {
> pc = base + index;
> - __init_page_cgroup(pc, start_pfn + index);
> + init_page_cgroup(pc, nid);
> }
> NODE_DATA(nid)->node_page_cgroup = base;
> total_usage += table_size;
> @@ -105,46 +114,50 @@ struct page_cgroup *lookup_page_cgroup(struct page *page)
> return section->page_cgroup + pfn;
> }
>
> +struct page *lookup_cgroup_page(struct page_cgroup *pc)
> +{
> + struct mem_section *section;
> + unsigned long nr;
> +
> + nr = page_cgroup_array_id(pc);
> + section = __nr_to_section(nr);
> + return pfn_to_page(pc - section->page_cgroup);
> +}
> +
> /* __alloc_bootmem...() is protected by !slab_available() */
> 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);
> } else {
> - /*
> - * We don't have to allocate page_cgroup again, but
> - * address of memmap may be changed. So, we have to initialize
> - * again.
> - */
> - base = section->page_cgroup + pfn;
> - table_size = 0;
> - /* check address of memmap is changed or not. */
> - if (base->page == pfn_to_page(pfn))
> - return 0;
> + 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);
>
> if (!base) {
> printk(KERN_ERR "page cgroup allocation failure\n");
> @@ -153,7 +166,7 @@ static int __init_refok init_section_page_cgroup(unsigned long pfn)
>
> for (index = 0; index < PAGES_PER_SECTION; index++) {
> pc = base + index;
> - __init_page_cgroup(pc, pfn + index);
> + init_page_cgroup(pc, nr);
> }
>
> section->page_cgroup = base - pfn;
> --
> 1.7.4
>
> --
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