Re: [PATCH 1/2] memcg: coalescing uncharge at unmap and truncation

[Hiroshi Shimamoto <h-shimamoto@ct.jp.nec.com>]

Hiroshi Shimamoto wrote:
> KAMEZAWA Hiroyuki wrote:
>> In massive parallel enviroment, res_counter can be a performance bottleneck.
>> One strong techinque to reduce lock contention is reducing calls by
>> coalescing some amount of calls into one.
>>
>> Considering charge/uncharge chatacteristic,
>> 	- charge is done one by one via demand-paging.
>> 	- uncharge is done by
>> 		- in chunk at munmap, truncate, exit, execve...
>> 		- one by one via vmscan/paging.
>>
>> It seems we have a chance in uncharge at unmap/truncation.
>>
>> This patch is a for coalescing uncharge. For avoiding scattering memcg's
>> structure to functions under /mm, this patch adds memcg batch uncharge
>> information to the task. 
>>
>> The degree of coalescing depends on callers
>>   - at invalidate/trucate... pagevec size
>>   - at unmap ....ZAP_BLOCK_SIZE
>> (memory itself will be freed in this degree.)
>> Then, we'll not coalescing too much.
>>
>> Changelog(now):
>>  - rebased onto the latest mmotm + softlimit fix patches.
>>
>> Changelog(old):
>>  - unified patch for callers
>>  - added commetns.
>>  - make ->do_batch as bool.
>>  - removed css_get() at el. We don't need it.
>>
>>
>> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
>> ---
>>  include/linux/memcontrol.h |   13 ++++++
>>  include/linux/sched.h      |    7 +++
>>  mm/memcontrol.c            |   91 ++++++++++++++++++++++++++++++++++++++++++---
>>  mm/memory.c                |    2 
>>  mm/truncate.c              |    6 ++
>>  5 files changed, 113 insertions(+), 6 deletions(-)
>>
>> Index: mmotm-2.6.31-Sep28/include/linux/memcontrol.h
>> ===================================================================
>> --- mmotm-2.6.31-Sep28.orig/include/linux/memcontrol.h
>> +++ mmotm-2.6.31-Sep28/include/linux/memcontrol.h
>> @@ -54,6 +54,11 @@ extern void mem_cgroup_rotate_lru_list(s
>>  extern void mem_cgroup_del_lru(struct page *page);
>>  extern void mem_cgroup_move_lists(struct page *page,
>>  				  enum lru_list from, enum lru_list to);
>> +
>> +/* For coalescing uncharge for reducing memcg' overhead*/
>> +extern void mem_cgroup_uncharge_start(void);
>> +extern void mem_cgroup_uncharge_end(void);
>> +
>>  extern void mem_cgroup_uncharge_page(struct page *page);
>>  extern void mem_cgroup_uncharge_cache_page(struct page *page);
>>  extern int mem_cgroup_shmem_charge_fallback(struct page *page,
>> @@ -151,6 +156,14 @@ static inline void mem_cgroup_cancel_cha
>>  {
>>  }
>>  
>> +static inline void mem_cgroup_uncharge_batch_start(void)
>> +{
>> +}
>> +
>> +static inline void mem_cgroup_uncharge_batch_start(void)
> 
> mem_cgroup_uncharge_batch_end?

s/_batch// too?

Thanks,
Hiroshi

> 
> 
> Thanks,
> Hiroshi
> 
>> +{
>> +}
>> +
>>  static inline void mem_cgroup_uncharge_page(struct page *page)
>>  {
>>  }
>> Index: mmotm-2.6.31-Sep28/mm/memcontrol.c
>> ===================================================================
>> --- mmotm-2.6.31-Sep28.orig/mm/memcontrol.c
>> +++ mmotm-2.6.31-Sep28/mm/memcontrol.c
>> @@ -1826,6 +1826,49 @@ void mem_cgroup_cancel_charge_swapin(str
>>  	css_put(&mem->css);
>>  }
>>  
>> +static void
>> +__do_uncharge(struct mem_cgroup *mem, const enum charge_type ctype)
>> +{
>> +	struct memcg_batch_info *batch = NULL;
>> +	bool uncharge_memsw = true;
>> +	/* If swapout, usage of swap doesn't decrease */
>> +	if (!do_swap_account || ctype == MEM_CGROUP_CHARGE_TYPE_SWAPOUT)
>> +		uncharge_memsw = false;
>> +	/*
>> +	 * do_batch > 0 when unmapping pages or inode invalidate/truncate.
>> +	 * In those cases, all pages freed continously can be expected to be in
>> +	 * the same cgroup and we have chance to coalesce uncharges.
>> +	 * And, we do uncharge one by one if this is killed by OOM.
>> +	 */
>> +	if (!current->memcg_batch.do_batch || test_thread_flag(TIF_MEMDIE))
>> +		goto direct_uncharge;
>> +
>> +	batch = &current->memcg_batch;
>> +	/*
>> +	 * In usual, we do css_get() when we remember memcg pointer.
>> +	 * But in this case, we keep res->usage until end of a series of
>> +	 * uncharges. Then, it's ok to ignore memcg's refcnt.
>> +	 */
>> +	if (!batch->memcg)
>> +		batch->memcg = mem;
>> +	/*
>> +	 * In typical case, batch->memcg == mem. This means we can
>> +	 * merge a series of uncharges to an uncharge of res_counter.
>> +	 * If not, we uncharge res_counter ony by one.
>> +	 */
>> +	if (batch->memcg != mem)
>> +		goto direct_uncharge;
>> +	/* remember freed charge and uncharge it later */
>> +	batch->pages += PAGE_SIZE;
>> +	if (uncharge_memsw)
>> +		batch->memsw += PAGE_SIZE;
>> +	return;
>> +direct_uncharge:
>> +	res_counter_uncharge(&mem->res, PAGE_SIZE);
>> +	if (uncharge_memsw)
>> +		res_counter_uncharge(&mem->memsw, PAGE_SIZE);
>> +	return;
>> +}
>>  
>>  /*
>>   * uncharge if !page_mapped(page)
>> @@ -1874,12 +1917,8 @@ __mem_cgroup_uncharge_common(struct page
>>  		break;
>>  	}
>>  
>> -	if (!mem_cgroup_is_root(mem)) {
>> -		res_counter_uncharge(&mem->res, PAGE_SIZE);
>> -		if (do_swap_account &&
>> -				(ctype != MEM_CGROUP_CHARGE_TYPE_SWAPOUT))
>> -			res_counter_uncharge(&mem->memsw, PAGE_SIZE);
>> -	}
>> +	if (!mem_cgroup_is_root(mem))
>> +		__do_uncharge(mem, ctype);
>>  	if (ctype == MEM_CGROUP_CHARGE_TYPE_SWAPOUT)
>>  		mem_cgroup_swap_statistics(mem, true);
>>  	mem_cgroup_charge_statistics(mem, pc, false);
>> @@ -1925,6 +1964,46 @@ void mem_cgroup_uncharge_cache_page(stru
>>  	__mem_cgroup_uncharge_common(page, MEM_CGROUP_CHARGE_TYPE_CACHE);
>>  }
>>  
>> +/*
>> + * batch_start/batch_end is called in unmap_page_range/invlidate/trucate.
>> + * In that cases, pages are freed continuously and we can expect pages
>> + * are in the same memcg. All these calls itself limits the number of
>> + * pages freed at once, then uncharge_start/end() is called properly.
>> + */
>> +
>> +void mem_cgroup_uncharge_start(void)
>> +{
>> +	if (!current->memcg_batch.do_batch) {
>> +		current->memcg_batch.memcg = NULL;
>> +		current->memcg_batch.pages = 0;
>> +		current->memcg_batch.memsw = 0;
>> +	}
>> +	current->memcg_batch.do_batch++;
>> +}
>> +
>> +void mem_cgroup_uncharge_end(void)
>> +{
>> +	struct mem_cgroup *mem;
>> +
>> +	if (!current->memcg_batch.do_batch)
>> +		return;
>> +
>> +	current->memcg_batch.do_batch--;
>> +	if (current->memcg_batch.do_batch) /* Nested ? */
>> +		return;
>> +
>> +	mem = current->memcg_batch.memcg;
>> +	if (!mem)
>> +		return;
>> +	/* This "mem" is valid bacause we hide charges behind us. */
>> +	if (current->memcg_batch.pages)
>> +		res_counter_uncharge(&mem->res, current->memcg_batch.pages);
>> +	if (current->memcg_batch.memsw)
>> +		res_counter_uncharge(&mem->memsw, current->memcg_batch.memsw);
>> +	/* Not necessary. but forget this pointer */
>> +	current->memcg_batch.memcg = NULL;
>> +}
>> +
>>  #ifdef CONFIG_SWAP
>>  /*
>>   * called after __delete_from_swap_cache() and drop "page" account.
>> Index: mmotm-2.6.31-Sep28/include/linux/sched.h
>> ===================================================================
>> --- mmotm-2.6.31-Sep28.orig/include/linux/sched.h
>> +++ mmotm-2.6.31-Sep28/include/linux/sched.h
>> @@ -1549,6 +1549,13 @@ struct task_struct {
>>  	unsigned long trace_recursion;
>>  #endif /* CONFIG_TRACING */
>>  	unsigned long stack_start;
>> +#ifdef CONFIG_CGROUP_MEM_RES_CTLR /* memcg uses this to do batch job */
>> +	struct memcg_batch_info {
>> +		int do_batch;
>> +		struct mem_cgroup *memcg;
>> +		long pages, memsw;
>> +	} memcg_batch;
>> +#endif
>>  };
>>  
>>  /* Future-safe accessor for struct task_struct's cpus_allowed. */
>> Index: mmotm-2.6.31-Sep28/mm/memory.c
>> ===================================================================
>> --- mmotm-2.6.31-Sep28.orig/mm/memory.c
>> +++ mmotm-2.6.31-Sep28/mm/memory.c
>> @@ -940,6 +940,7 @@ static unsigned long unmap_page_range(st
>>  		details = NULL;
>>  
>>  	BUG_ON(addr >= end);
>> +	mem_cgroup_uncharge_start();
>>  	tlb_start_vma(tlb, vma);
>>  	pgd = pgd_offset(vma->vm_mm, addr);
>>  	do {
>> @@ -952,6 +953,7 @@ static unsigned long unmap_page_range(st
>>  						zap_work, details);
>>  	} while (pgd++, addr = next, (addr != end && *zap_work > 0));
>>  	tlb_end_vma(tlb, vma);
>> +	mem_cgroup_uncharge_end();
>>  
>>  	return addr;
>>  }
>> Index: mmotm-2.6.31-Sep28/mm/truncate.c
>> ===================================================================
>> --- mmotm-2.6.31-Sep28.orig/mm/truncate.c
>> +++ mmotm-2.6.31-Sep28/mm/truncate.c
>> @@ -272,6 +272,7 @@ void truncate_inode_pages_range(struct a
>>  			pagevec_release(&pvec);
>>  			break;
>>  		}
>> +		mem_cgroup_uncharge_start();
>>  		for (i = 0; i < pagevec_count(&pvec); i++) {
>>  			struct page *page = pvec.pages[i];
>>  
>> @@ -286,6 +287,7 @@ void truncate_inode_pages_range(struct a
>>  			unlock_page(page);
>>  		}
>>  		pagevec_release(&pvec);
>> +		mem_cgroup_uncharge_end();
>>  	}
>>  }
>>  EXPORT_SYMBOL(truncate_inode_pages_range);
>> @@ -327,6 +329,7 @@ unsigned long invalidate_mapping_pages(s
>>  	pagevec_init(&pvec, 0);
>>  	while (next <= end &&
>>  			pagevec_lookup(&pvec, mapping, next, PAGEVEC_SIZE)) {
>> +		mem_cgroup_uncharge_start();
>>  		for (i = 0; i < pagevec_count(&pvec); i++) {
>>  			struct page *page = pvec.pages[i];
>>  			pgoff_t index;
>> @@ -354,6 +357,7 @@ unsigned long invalidate_mapping_pages(s
>>  				break;
>>  		}
>>  		pagevec_release(&pvec);
>> +		mem_cgroup_uncharge_end();
>>  		cond_resched();
>>  	}
>>  	return ret;
>> @@ -428,6 +432,7 @@ int invalidate_inode_pages2_range(struct
>>  	while (next <= end && !wrapped &&
>>  		pagevec_lookup(&pvec, mapping, next,
>>  			min(end - next, (pgoff_t)PAGEVEC_SIZE - 1) + 1)) {
>> +		mem_cgroup_uncharge_start();
>>  		for (i = 0; i < pagevec_count(&pvec); i++) {
>>  			struct page *page = pvec.pages[i];
>>  			pgoff_t page_index;
>> @@ -477,6 +482,7 @@ int invalidate_inode_pages2_range(struct
>>  			unlock_page(page);
>>  		}
>>  		pagevec_release(&pvec);
>> +		mem_cgroup_uncharge_end();
>>  		cond_resched();
>>  	}
>>  	return ret;
>>
>> --
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>>
>>
> 
>