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


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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