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SubjectRe: [RFC][PATCH] Remove cgroup member from struct page
On Mon, 8 Sep 2008 20:58:10 +0530
Balbir Singh <balbir@linux.vnet.ibm.com> wrote:
> Sorry for the delay in sending out the new patch, I am traveling and
> thus a little less responsive. Here is the update patch
>
>
Hmm.. I've considered this approach for a while and my answer is that
this is not what you really want.

Because you just moves the placement of pointer from memmap to
radix_tree both in GFP_KERNEL, total kernel memory usage is not changed.
So, at least, you have to add some address calculation (as I did in March)
to getting address of page_cgroup. But page_cgroup itself consumes 32bytes
per page. Then.....

My proposal to 32bit system is following
- remove page_cgroup completely.
- As a result, there is no per-cgroup lru. But it will not be bad
bacause the number of cgroups and pages are not big.
just a trade-off between kernel-memory-space v.s. speed.
- Removing page_cgroup and just remember address of mem_cgroup per page.

How do you think ?

Thanks,
-Kame


> v3...v2
> 1. Convert flags to unsigned long
> 2. Move page_cgroup->lock to a bit spin lock in flags
>
> v2...v1
>
> 1. Fix a small bug, don't call radix_tree_preload_end(), if preload fails
>
> This is a rewrite of a patch I had written long back to remove struct page
> (I shared the patches with Kamezawa, but never posted them anywhere else).
> I spent the weekend, cleaning them up for 2.6.27-rc5-mmotm (29 Aug 2008).
>
> I've tested the patches on an x86_64 box, I've run a simple test running
> under the memory control group and the same test running concurrently under
> two different groups (and creating pressure within their groups). I've also
> compiled the patch with CGROUP_MEM_RES_CTLR turned off.
>
> Advantages of the patch
>
> 1. It removes the extra pointer in struct page
>
> Disadvantages
>
> 1. Radix tree lookup is not an O(1) operation, once the page is known
> getting to the page_cgroup (pc) is a little more expensive now.
>
> This is an initial RFC for comments
>
> TODOs
>
> 1. Test the page migration changes
>
> Performance
>
> In a unixbench run, these patches had a performance impact of 2% (slowdown).
>
> Comments/Reviews?
>
> Signed-off-by: Balbir Singh <balbir@linux.vnet.ibm.com>
> ---
>
> include/linux/memcontrol.h | 23 +++++
> include/linux/mm_types.h | 4
> mm/memcontrol.c | 187 +++++++++++++++++++++++++++++----------------
> 3 files changed, 144 insertions(+), 70 deletions(-)
>
> diff -puN mm/memcontrol.c~memcg_move_to_radix_tree mm/memcontrol.c
> --- linux-2.6.27-rc5/mm/memcontrol.c~memcg_move_to_radix_tree 2008-09-04 15:45:54.000000000 +0530
> +++ linux-2.6.27-rc5-balbir/mm/memcontrol.c 2008-09-08 20:15:30.000000000 +0530
> @@ -24,6 +24,7 @@
> #include <linux/smp.h>
> #include <linux/page-flags.h>
> #include <linux/backing-dev.h>
> +#include <linux/radix-tree.h>
> #include <linux/bit_spinlock.h>
> #include <linux/rcupdate.h>
> #include <linux/slab.h>
> @@ -40,6 +41,9 @@ struct cgroup_subsys mem_cgroup_subsys _
> static struct kmem_cache *page_cgroup_cache __read_mostly;
> #define MEM_CGROUP_RECLAIM_RETRIES 5
>
> +static struct radix_tree_root mem_cgroup_tree;
> +static spinlock_t mem_cgroup_tree_lock;
> +
> /*
> * Statistics for memory cgroup.
> */
> @@ -137,20 +141,6 @@ struct mem_cgroup {
> static struct mem_cgroup init_mem_cgroup;
>
> /*
> - * We use the lower bit of the page->page_cgroup pointer as a bit spin
> - * lock. We need to ensure that page->page_cgroup is at least two
> - * byte aligned (based on comments from Nick Piggin). But since
> - * bit_spin_lock doesn't actually set that lock bit in a non-debug
> - * uniprocessor kernel, we should avoid setting it here too.
> - */
> -#define PAGE_CGROUP_LOCK_BIT 0x0
> -#if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
> -#define PAGE_CGROUP_LOCK (1 << PAGE_CGROUP_LOCK_BIT)
> -#else
> -#define PAGE_CGROUP_LOCK 0x0
> -#endif
> -
> -/*
> * A page_cgroup page is associated with every page descriptor. The
> * page_cgroup helps us identify information about the cgroup
> */
> @@ -158,12 +148,17 @@ struct page_cgroup {
> struct list_head lru; /* per cgroup LRU list */
> struct page *page;
> struct mem_cgroup *mem_cgroup;
> - int flags;
> + unsigned long flags;
> };
> -#define PAGE_CGROUP_FLAG_CACHE (0x1) /* charged as cache */
> -#define PAGE_CGROUP_FLAG_ACTIVE (0x2) /* page is active in this cgroup */
> -#define PAGE_CGROUP_FLAG_FILE (0x4) /* page is file system backed */
> -#define PAGE_CGROUP_FLAG_UNEVICTABLE (0x8) /* page is unevictableable */
> +
> +/*
> + * LOCK_BIT is 0, with value 1
> + */
> +#define PAGE_CGROUP_FLAG_LOCK_BIT (0x0) /* lock bit */
> +#define PAGE_CGROUP_FLAG_CACHE (0x2) /* charged as cache */
> +#define PAGE_CGROUP_FLAG_ACTIVE (0x4) /* page is active in this cgroup */
> +#define PAGE_CGROUP_FLAG_FILE (0x8) /* page is file system backed */
> +#define PAGE_CGROUP_FLAG_UNEVICTABLE (0x10)/* page is unevictableable */
>
> static int page_cgroup_nid(struct page_cgroup *pc)
> {
> @@ -248,35 +243,81 @@ struct mem_cgroup *mem_cgroup_from_task(
> struct mem_cgroup, css);
> }
>
> -static inline int page_cgroup_locked(struct page *page)
> +static inline void lock_page_cgroup(struct page_cgroup *pc)
> {
> - return bit_spin_is_locked(PAGE_CGROUP_LOCK_BIT, &page->page_cgroup);
> + bit_spin_lock(PAGE_CGROUP_FLAG_LOCK_BIT, &pc->flags);
> }
>
> -static void page_assign_page_cgroup(struct page *page, struct page_cgroup *pc)
> +static inline int trylock_page_cgroup(struct page_cgroup *pc)
> {
> - VM_BUG_ON(!page_cgroup_locked(page));
> - page->page_cgroup = ((unsigned long)pc | PAGE_CGROUP_LOCK);
> + return bit_spin_trylock(PAGE_CGROUP_FLAG_LOCK_BIT, &pc->flags);
> }
>
> -struct page_cgroup *page_get_page_cgroup(struct page *page)
> +static inline void unlock_page_cgroup(struct page_cgroup *pc)
> {
> - return (struct page_cgroup *) (page->page_cgroup & ~PAGE_CGROUP_LOCK);
> + bit_spin_unlock(PAGE_CGROUP_FLAG_LOCK_BIT, &pc->flags);
> }
>
> -static void lock_page_cgroup(struct page *page)
> +static int page_assign_page_cgroup(struct page *page, struct page_cgroup *pc,
> + gfp_t gfp_mask)
> {
> - bit_spin_lock(PAGE_CGROUP_LOCK_BIT, &page->page_cgroup);
> -}
> + unsigned long pfn = page_to_pfn(page);
> + unsigned long flags;
> + int err = 0;
> + struct page_cgroup *old_pc;
>
> -static int try_lock_page_cgroup(struct page *page)
> -{
> - return bit_spin_trylock(PAGE_CGROUP_LOCK_BIT, &page->page_cgroup);
> + if (pc) {
> + err = radix_tree_preload(gfp_mask & ~__GFP_HIGHMEM);
> + if (err) {
> + printk(KERN_WARNING "could not preload radix tree "
> + "in %s\n", __func__);
> + goto done;
> + }
> + }
> +
> + spin_lock_irqsave(&mem_cgroup_tree_lock, flags);
> + old_pc = radix_tree_lookup(&mem_cgroup_tree, pfn);
> + if (pc && old_pc) {
> + err = -EEXIST;
> + goto pc_race;
> + }
> + if (pc) {
> + err = radix_tree_insert(&mem_cgroup_tree, pfn, pc);
> + if (err)
> + printk(KERN_WARNING "Inserting into radix tree failed "
> + "in %s\n", __func__);
> + } else
> + radix_tree_delete(&mem_cgroup_tree, pfn);
> +pc_race:
> + spin_unlock_irqrestore(&mem_cgroup_tree_lock, flags);
> + if (pc)
> + radix_tree_preload_end();
> +done:
> + return err;
> }
>
> -static void unlock_page_cgroup(struct page *page)
> +struct page_cgroup *__page_get_page_cgroup(struct page *page, bool lock,
> + bool trylock)
> {
> - bit_spin_unlock(PAGE_CGROUP_LOCK_BIT, &page->page_cgroup);
> + unsigned long pfn = page_to_pfn(page);
> + struct page_cgroup *pc;
> + int ret;
> +
> + rcu_read_lock();
> + pc = radix_tree_lookup(&mem_cgroup_tree, pfn);
> +
> + if (pc && lock)
> + lock_page_cgroup(pc);
> +
> + if (pc && trylock) {
> + ret = trylock_page_cgroup(pc);
> + if (!ret)
> + pc = NULL;
> + }
> +
> + rcu_read_unlock();
> +
> + return pc;
> }
>
> static void __mem_cgroup_remove_list(struct mem_cgroup_per_zone *mz,
> @@ -377,17 +418,15 @@ void mem_cgroup_move_lists(struct page *
> * safely get to page_cgroup without it, so just try_lock it:
> * mem_cgroup_isolate_pages allows for page left on wrong list.
> */
> - if (!try_lock_page_cgroup(page))
> + pc = page_get_page_cgroup_trylock(page);
> + if (!pc)
> return;
>
> - pc = page_get_page_cgroup(page);
> - if (pc) {
> - mz = page_cgroup_zoneinfo(pc);
> - spin_lock_irqsave(&mz->lru_lock, flags);
> - __mem_cgroup_move_lists(pc, lru);
> - spin_unlock_irqrestore(&mz->lru_lock, flags);
> - }
> - unlock_page_cgroup(page);
> + mz = page_cgroup_zoneinfo(pc);
> + spin_lock_irqsave(&mz->lru_lock, flags);
> + __mem_cgroup_move_lists(pc, lru);
> + spin_unlock_irqrestore(&mz->lru_lock, flags);
> + unlock_page_cgroup(pc);
> }
>
> /*
> @@ -516,7 +555,7 @@ static int mem_cgroup_charge_common(stru
> struct mem_cgroup *memcg)
> {
> struct mem_cgroup *mem;
> - struct page_cgroup *pc;
> + struct page_cgroup *pc, *old_pc;
> unsigned long flags;
> unsigned long nr_retries = MEM_CGROUP_RECLAIM_RETRIES;
> struct mem_cgroup_per_zone *mz;
> @@ -569,35 +608,49 @@ static int mem_cgroup_charge_common(stru
>
> pc->mem_cgroup = mem;
> pc->page = page;
> + pc->flags = 0; /* No lock, no other bits either */
> +
> /*
> * If a page is accounted as a page cache, insert to inactive list.
> * If anon, insert to active list.
> */
> if (ctype == MEM_CGROUP_CHARGE_TYPE_CACHE) {
> - pc->flags = PAGE_CGROUP_FLAG_CACHE;
> + pc->flags |= PAGE_CGROUP_FLAG_CACHE;
> if (page_is_file_cache(page))
> pc->flags |= PAGE_CGROUP_FLAG_FILE;
> else
> pc->flags |= PAGE_CGROUP_FLAG_ACTIVE;
> } else
> - pc->flags = PAGE_CGROUP_FLAG_ACTIVE;
> + pc->flags |= PAGE_CGROUP_FLAG_ACTIVE;
> +
> + old_pc = page_get_page_cgroup_locked(page);
> + if (old_pc) {
> + unlock_page_cgroup(old_pc);
> + res_counter_uncharge(&mem->res, PAGE_SIZE);
> + css_put(&mem->css);
> + kmem_cache_free(page_cgroup_cache, pc);
> + goto done;
> + }
>
> - lock_page_cgroup(page);
> - if (unlikely(page_get_page_cgroup(page))) {
> - unlock_page_cgroup(page);
> + lock_page_cgroup(pc);
> + /*
> + * page_get_page_cgroup() does not necessarily guarantee that
> + * there will be no race in checking for pc, page_assign_page_pc()
> + * will definitely catch it.
> + */
> + if (page_assign_page_cgroup(page, pc, gfp_mask)) {
> + unlock_page_cgroup(pc);
> res_counter_uncharge(&mem->res, PAGE_SIZE);
> css_put(&mem->css);
> kmem_cache_free(page_cgroup_cache, pc);
> goto done;
> }
> - page_assign_page_cgroup(page, pc);
>
> mz = page_cgroup_zoneinfo(pc);
> spin_lock_irqsave(&mz->lru_lock, flags);
> __mem_cgroup_add_list(mz, pc);
> spin_unlock_irqrestore(&mz->lru_lock, flags);
> -
> - unlock_page_cgroup(page);
> + unlock_page_cgroup(pc);
> done:
> return 0;
> out:
> @@ -645,15 +698,13 @@ int mem_cgroup_cache_charge(struct page
> if (!(gfp_mask & __GFP_WAIT)) {
> struct page_cgroup *pc;
>
> - lock_page_cgroup(page);
> - pc = page_get_page_cgroup(page);
> + pc = page_get_page_cgroup_locked(page);
> if (pc) {
> VM_BUG_ON(pc->page != page);
> VM_BUG_ON(!pc->mem_cgroup);
> - unlock_page_cgroup(page);
> + unlock_page_cgroup(pc);
> return 0;
> }
> - unlock_page_cgroup(page);
> }
>
> if (unlikely(!mm))
> @@ -673,6 +724,7 @@ __mem_cgroup_uncharge_common(struct page
> struct mem_cgroup *mem;
> struct mem_cgroup_per_zone *mz;
> unsigned long flags;
> + int ret;
>
> if (mem_cgroup_subsys.disabled)
> return;
> @@ -680,8 +732,7 @@ __mem_cgroup_uncharge_common(struct page
> /*
> * Check if our page_cgroup is valid
> */
> - lock_page_cgroup(page);
> - pc = page_get_page_cgroup(page);
> + pc = page_get_page_cgroup_locked(page);
> if (unlikely(!pc))
> goto unlock;
>
> @@ -697,8 +748,9 @@ __mem_cgroup_uncharge_common(struct page
> __mem_cgroup_remove_list(mz, pc);
> spin_unlock_irqrestore(&mz->lru_lock, flags);
>
> - page_assign_page_cgroup(page, NULL);
> - unlock_page_cgroup(page);
> + ret = page_assign_page_cgroup(page, NULL, GFP_KERNEL);
> + VM_BUG_ON(ret);
> + unlock_page_cgroup(pc);
>
> mem = pc->mem_cgroup;
> res_counter_uncharge(&mem->res, PAGE_SIZE);
> @@ -707,7 +759,14 @@ __mem_cgroup_uncharge_common(struct page
> kmem_cache_free(page_cgroup_cache, pc);
> return;
> unlock:
> - unlock_page_cgroup(page);
> + unlock_page_cgroup(pc);
> +}
> +
> +void page_reset_bad_cgroup(struct page *page)
> +{
> + int ret;
> + ret = page_assign_page_cgroup(page, NULL, GFP_KERNEL);
> + VM_BUG_ON(ret);
> }
>
> void mem_cgroup_uncharge_page(struct page *page)
> @@ -734,15 +793,14 @@ int mem_cgroup_prepare_migration(struct
> if (mem_cgroup_subsys.disabled)
> return 0;
>
> - lock_page_cgroup(page);
> - pc = page_get_page_cgroup(page);
> + pc = page_get_page_cgroup_locked(page);
> if (pc) {
> mem = pc->mem_cgroup;
> css_get(&mem->css);
> if (pc->flags & PAGE_CGROUP_FLAG_CACHE)
> ctype = MEM_CGROUP_CHARGE_TYPE_CACHE;
> + unlock_page_cgroup(pc);
> }
> - unlock_page_cgroup(page);
> if (mem) {
> ret = mem_cgroup_charge_common(newpage, NULL, GFP_KERNEL,
> ctype, mem);
> @@ -1107,6 +1165,7 @@ mem_cgroup_create(struct cgroup_subsys *
> if (unlikely((cont->parent) == NULL)) {
> mem = &init_mem_cgroup;
> page_cgroup_cache = KMEM_CACHE(page_cgroup, SLAB_PANIC);
> + spin_lock_init(&mem_cgroup_tree_lock);
> } else {
> mem = mem_cgroup_alloc();
> if (!mem)
> diff -puN include/linux/memcontrol.h~memcg_move_to_radix_tree include/linux/memcontrol.h
> --- linux-2.6.27-rc5/include/linux/memcontrol.h~memcg_move_to_radix_tree 2008-09-04 15:45:54.000000000 +0530
> +++ linux-2.6.27-rc5-balbir/include/linux/memcontrol.h 2008-09-04 15:45:54.000000000 +0530
> @@ -27,9 +27,28 @@ struct mm_struct;
>
> #ifdef CONFIG_CGROUP_MEM_RES_CTLR
>
> -#define page_reset_bad_cgroup(page) ((page)->page_cgroup = 0)
> +extern void page_reset_bad_cgroup(struct page *page);
> +extern struct page_cgroup *__page_get_page_cgroup(struct page *page, bool lock,
> + bool trylock);
> +
> +static __always_inline
> +struct page_cgroup *page_get_page_cgroup(struct page *page)
> +{
> + return __page_get_page_cgroup(page, false, false);
> +}
> +
> +static __always_inline
> +struct page_cgroup *page_get_page_cgroup_trylock(struct page *page)
> +{
> + return __page_get_page_cgroup(page, false, true);
> +}
> +
> +static __always_inline
> +struct page_cgroup *page_get_page_cgroup_locked(struct page *page)
> +{
> + return __page_get_page_cgroup(page, true, false);
> +}
>
> -extern struct page_cgroup *page_get_page_cgroup(struct page *page);
> extern int mem_cgroup_charge(struct page *page, struct mm_struct *mm,
> gfp_t gfp_mask);
> extern int mem_cgroup_cache_charge(struct page *page, struct mm_struct *mm,
> diff -puN include/linux/mm_types.h~memcg_move_to_radix_tree include/linux/mm_types.h
> --- linux-2.6.27-rc5/include/linux/mm_types.h~memcg_move_to_radix_tree 2008-09-04 15:45:54.000000000 +0530
> +++ linux-2.6.27-rc5-balbir/include/linux/mm_types.h 2008-09-04 15:45:54.000000000 +0530
> @@ -92,10 +92,6 @@ struct page {
> void *virtual; /* Kernel virtual address (NULL if
> not kmapped, ie. highmem) */
> #endif /* WANT_PAGE_VIRTUAL */
> -#ifdef CONFIG_CGROUP_MEM_RES_CTLR
> - unsigned long page_cgroup;
> -#endif
> -
> #ifdef CONFIG_KMEMCHECK
> void *shadow;
> #endif
> diff -puN mm/page_alloc.c~memcg_move_to_radix_tree mm/page_alloc.c
> _
>
> --
> Balbir
>



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