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Subject[mmotm][PATCH] coalescing uncharge
Based on mmotm+ softlimit clean up patches I posted today.

I think this version is much easier to read and cleaner than previous one.
But it's -rc8 age now. I can wait until the end of next merge window.

after make -j8 kernel.
==
lock_stat version 0.3
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
class name con-bounces contentions waittime-min waittime-max waittime-total acq-bounces acquisitions holdtime-min holdtime-max holdtime-total
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
&counter->lock: 3074759 3086077 0.94 14372.27 1978508.38 68039606 80763359 0.45 34243.51 37892635.86
--------------
&counter->lock 2970383 [<ffffffff8109921d>] res_counter_charge+0x4d
&counter->lock 112516 [<ffffffff81099175>] res_counter_uncharge+0x35
&counter->lock 3178 [<ffffffff81111e2a>] mem_cgroup_update_tree+0x11a/0x1c0
--------------
&counter->lock 2973905 [<ffffffff8109921d>] res_counter_charge+0x4d
&counter->lock 109581 [<ffffffff81099175>] res_counter_uncharge+0x35
&counter->lock 2591 [<ffffffff81111e2a>] mem_cgroup_update_tree+0x11a/0x1c0
==
After this patch, lock conention in uncharge is reduced.
(And I know if I can reduce lock contention in charge path,
this dramatically reduced.)

==
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

In massive parallel enviroment, res_counter can be a performance bottleneck.
This patch is a trial for reducing lock contention.
One strong techinque to reduce lock contention is reducing calls by
batching some amount of calls int 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 hace a chance to batched-uncharge.
This patch is a base patch for batched uncharge. For avoiding
scattering memcg's structure, this patch adds memcg batch uncharge
information to the task. please see start/end usage in next patch.
Because it will be used always at exit(), it's not very costly.
(And much gives us much easier code than using percpu_xxx.)

The degree of coalescing depends on callers
- at invalidate/trucate... pagevec size
- at unmap ....ZAP_BLOCK_SIZE
pages itself will be freed in this degree.
Changelog:
- 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 | 12 ++++++
include/linux/sched.h | 7 +++
mm/memcontrol.c | 90 ++++++++++++++++++++++++++++++++++++++++++---
mm/memory.c | 2 +
mm/truncate.c | 6 +++
5 files changed, 111 insertions(+), 6 deletions(-)
Index: mmotm-2.6.31-Aug27/include/linux/memcontrol.h
===================================================================
--- mmotm-2.6.31-Aug27.orig/include/linux/memcontrol.h
+++ mmotm-2.6.31-Aug27/include/linux/memcontrol.h
@@ -54,6 +54,10 @@ 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);
+
+extern void mem_cgroup_uncharge_batch_start(void);
+extern void mem_cgroup_uncharge_batch_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 +155,14 @@ 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)
+{
+}
+
static inline void mem_cgroup_uncharge_page(struct page *page)
{
}
Index: mmotm-2.6.31-Aug27/mm/memcontrol.c
===================================================================
--- mmotm-2.6.31-Aug27.orig/mm/memcontrol.c
+++ mmotm-2.6.31-Aug27/mm/memcontrol.c
@@ -1821,6 +1821,48 @@ 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 == true when unmapping pages or inode invaludate/truncate.
+ * In those cases, all pages freed continously can be expected to be in
+ * the same cgroup and we have chance to coalesce uncharges.
+ */
+ if (!current->memcg_batch.do_batch)
+ 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)
@@ -1869,12 +1911,8 @@ __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);
@@ -1920,6 +1958,46 @@ 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_batch_start(void)
+{
+ VM_BUG_ON(current->memcg_batch.do_batch);
+ /* avoid batch if killed by OOM */
+ if (test_thread_flag(TIF_MEMDIE))
+ return;
+ current->memcg_batch.memcg = NULL;
+ current->memcg_batch.pages = 0;
+ current->memcg_batch.memsw = 0;
+ current->memcg_batch.do_batch = true;
+}
+
+void mem_cgroup_uncharge_batch_end(void)
+{
+ struct mem_cgroup *mem;
+
+ if (!current->memcg_batch.do_batch)
+ return;
+
+ current->memcg_batch.do_batch = false;
+
+ 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-Aug27/include/linux/sched.h
===================================================================
--- mmotm-2.6.31-Aug27.orig/include/linux/sched.h
+++ mmotm-2.6.31-Aug27/include/linux/sched.h
@@ -1540,6 +1540,13 @@ 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 {
+ bool 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-Aug27/mm/memory.c
===================================================================
--- mmotm-2.6.31-Aug27.orig/mm/memory.c
+++ mmotm-2.6.31-Aug27/mm/memory.c
@@ -909,6 +909,7 @@ static unsigned long unmap_page_range(st
details = NULL;

BUG_ON(addr >= end);
+ mem_cgroup_uncharge_batch_start();
tlb_start_vma(tlb, vma);
pgd = pgd_offset(vma->vm_mm, addr);
do {
@@ -921,6 +922,7 @@ 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_batch_end();

return addr;
}
Index: mmotm-2.6.31-Aug27/mm/truncate.c
===================================================================
--- mmotm-2.6.31-Aug27.orig/mm/truncate.c
+++ mmotm-2.6.31-Aug27/mm/truncate.c
@@ -272,6 +272,7 @@ void truncate_inode_pages_range(struct a
pagevec_release(&pvec);
break;
}
+ mem_cgroup_uncharge_batch_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_batch_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_batch_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_batch_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_batch_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_batch_end();
cond_resched();
}
return ret;


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