memcg: coalesce uncharge during unmap/truncate

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 to coalesce uncharges for improving scalability 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. A reason for per-task batching is for making use of caller's context information. We do batched uncharge (deleyed uncharge) when truncation/unmap occurs but do direct uncharge when uncharge is called by memory reclaim (vmscan.c). 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. On x86-64 8cpu server, I tested overheads of memcg at page fault by running a program which does map/fault/unmap in a loop. Running a task per a cpu by taskset and see sum of the number of page faults in 60secs. [without memcg config] 40156968 page-faults # 0.085 M/sec ( +- 0.046% ) 27.67 cache-miss/faults [root cgroup] 36659599 page-faults # 0.077 M/sec ( +- 0.247% ) 31.58 miss/faults [in a child cgroup] 18444157 page-faults # 0.039 M/sec ( +- 0.133% ) 69.96 miss/faults [child with this patch] 27133719 page-faults # 0.057 M/sec ( +- 0.155% ) 47.16 miss/faults We can see some amounts of improvement. (root cgroup doesn't affected by this patch) Another patch for "charge" will follow this and above will be improved more. Changelog(since 2009/10/02): - renamed filed of memcg_batch (as pages to bytes, memsw to memsw_bytes) - some clean up and commentary/description updates. - added initialize code to copy_process(). (possible bug fix) Changelog(old): - fixed !CONFIG_MEM_CGROUP case. - rebased onto the latest mmotm + softlimit fix patches. - 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> Cc: Balbir Singh <balbir@in.ibm.com> Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-12-15 16:47:03 -08:00 · 2009-12-15 16:47:03 -08:00 · 569b846df5
commit 569b846df5
parent cd9b45b78a
6 changed files with 123 additions and 6 deletions
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@ -54,6 +54,11 @@ extern void mem_cgroup_rotate_lru_list(struct page *page, enum lru_list lru);
 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_charge_swapin(struct mem_cgroup *ptr)
 {
 }

+static inline void mem_cgroup_uncharge_start(void)
+{
+}
+
+static inline void mem_cgroup_uncharge_end(void)
+{
+}
+
 static inline void mem_cgroup_uncharge_page(struct page *page)
 {
 }
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@ -1544,6 +1544,14 @@ 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;	/* incremented when batch uncharge started */
+		struct mem_cgroup *memcg; /* target memcg of uncharge */
+		unsigned long bytes; 		/* uncharged usage */
+		unsigned long memsw_bytes; /* uncharged mem+swap usage */
+	} memcg_batch;
+#endif
 };

 /* Future-safe accessor for struct task_struct's cpus_allowed. */
--- a/kernel/fork.c
+++ b/kernel/fork.c
@ -1127,6 +1127,10 @@ static struct task_struct *copy_process(unsigned long clone_flags,
 #ifdef CONFIG_DEBUG_MUTEXES
 	p->blocked_on = NULL; /* not blocked yet */
 #endif
+#ifdef CONFIG_CGROUP_MEM_RES_CTLR
+	p->memcg_batch.do_batch = 0;
+	p->memcg_batch.memcg = NULL;
+#endif

 	p->bts = NULL;

--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@ -1827,6 +1827,50 @@ void mem_cgroup_cancel_charge_swapin(struct mem_cgroup *mem)
 	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.
+	 * But we do uncharge one by one if this is killed by OOM(TIF_MEMDIE)
+	 * because we want to do uncharge as soon as possible.
+	 */
+	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->bytes += PAGE_SIZE;
+	if (uncharge_memsw)
+		batch->memsw_bytes += 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)
@ -1875,12 +1919,8 @@ __mem_cgroup_uncharge_common(struct page *page, enum charge_type ctype)
 		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);
@ -1926,6 +1966,50 @@ void mem_cgroup_uncharge_cache_page(struct page *page)
 	__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.
+ * This may be called prural(2) times in a context,
+ */
+
+void mem_cgroup_uncharge_start(void)
+{
+	current->memcg_batch.do_batch++;
+	/* We can do nest. */
+	if (current->memcg_batch.do_batch == 1) {
+		current->memcg_batch.memcg = NULL;
+		current->memcg_batch.bytes = 0;
+		current->memcg_batch.memsw_bytes = 0;
+	}
+}
+
+void mem_cgroup_uncharge_end(void)
+{
+	struct memcg_batch_info *batch = &current->memcg_batch;
+
+	if (!batch->do_batch)
+		return;
+
+	batch->do_batch--;
+	if (batch->do_batch) /* If stacked, do nothing. */
+		return;
+
+	if (!batch->memcg)
+		return;
+	/*
+	 * This "batch->memcg" is valid without any css_get/put etc...
+	 * bacause we hide charges behind us.
+	 */
+	if (batch->bytes)
+		res_counter_uncharge(&batch->memcg->res, batch->bytes);
+	if (batch->memsw_bytes)
+		res_counter_uncharge(&batch->memcg->memsw, batch->memsw_bytes);
+	/* forget this pointer (for sanity check) */
+	batch->memcg = NULL;
+}
+
 #ifdef CONFIG_SWAP
 /*
 * called after __delete_from_swap_cache() and drop "page" account.
--- a/mm/memory.c
+++ b/mm/memory.c
@ -956,6 +956,7 @@ static unsigned long unmap_page_range(struct mmu_gather *tlb,
 		details = NULL;

 	BUG_ON(addr >= end);
+	mem_cgroup_uncharge_start();
 	tlb_start_vma(tlb, vma);
 	pgd = pgd_offset(vma->vm_mm, addr);
 	do {
@ -968,6 +969,7 @@ static unsigned long unmap_page_range(struct mmu_gather *tlb,
 						zap_work, details);
 	} while (pgd++, addr = next, (addr != end && *zap_work > 0));
 	tlb_end_vma(tlb, vma);
+	mem_cgroup_uncharge_end();

 	return addr;
 }
--- a/mm/truncate.c
+++ b/mm/truncate.c
@ -272,6 +272,7 @@ void truncate_inode_pages_range(struct address_space *mapping,
 			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 address_space *mapping,
 			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(struct address_space *mapping,
 	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(struct address_space *mapping,
 				break;
 		}
 		pagevec_release(&pvec);
+		mem_cgroup_uncharge_end();
 		cond_resched();
 	}
 	return ret;
@ -428,6 +432,7 @@ int invalidate_inode_pages2_range(struct address_space *mapping,
 	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 address_space *mapping,
 			unlock_page(page);
 		}
 		pagevec_release(&pvec);
+		mem_cgroup_uncharge_end();
 		cond_resched();
 	}
 	return ret;