From mboxrd@z Thu Jan 1 00:00:00 1970 From: Greg Thelen Subject: Re: [PATCH v8 10/12] memcg: create support routines for page-writeback Date: Mon, 06 Jun 2011 11:47:03 -0700 Message-ID: References: <1307117538-14317-1-git-send-email-gthelen@google.com> <1307117538-14317-11-git-send-email-gthelen@google.com> <20110605031156.GB5914@barrios-laptop> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Sender: owner-linux-mm@kvack.org To: Minchan Kim Cc: Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org, containers@lists.osdl.org, linux-fsdevel@vger.kernel.org, Andrea Righi , Balbir Singh , KAMEZAWA Hiroyuki , Daisuke Nishimura , Johannes Weiner , Ciju Rajan K , David Rientjes , Wu Fengguang , Vivek Goyal , Dave Chinner List-Id: containers.vger.kernel.org Minchan Kim writes: > Hi Greg, > > On Fri, Jun 03, 2011 at 09:12:16AM -0700, Greg Thelen wrote: >> Introduce memcg routines to assist in per-memcg dirty page management: >> >> - mem_cgroup_balance_dirty_pages() walks a memcg hierarchy comparing >> dirty memory usage against memcg foreground and background thresholds. >> If an over-background-threshold memcg is found, then per-memcg >> background writeback is queued. Per-memcg writeback differs from >> classic, non-memcg, per bdi writeback by setting the new >> writeback_control.for_cgroup bit. >> >> If an over-foreground-threshold memcg is found, then foreground >> writeout occurs. When performing foreground writeout, first consider >> inodes exclusive to the memcg. If unable to make enough progress, >> then consider inodes shared between memcg. Such cross-memcg inode >> sharing likely to be rare in situations that use per-cgroup memory >> isolation. The approach tries to handle the common (non-shared) >> case well without punishing well behaved (non-sharing) cgroups. >> As a last resort writeback shared inodes. >> >> This routine is used by balance_dirty_pages() in a later change. >> >> - mem_cgroup_hierarchical_dirty_info() returns the dirty memory usage >> and limits of the memcg closest to (or over) its dirty limit. This >> will be used by throttle_vm_writeout() in a latter change. >> >> Signed-off-by: Greg Thelen >> --- >> Changelog since v7: >> - Add more detail to commit description. >> >> - Declare the new writeback_control for_cgroup bit in this change, the >> first patch that uses the new field is first used. In -v7 the field >> was declared in a separate patch. >> >> include/linux/memcontrol.h | 18 +++++ >> include/linux/writeback.h | 1 + >> include/trace/events/memcontrol.h | 83 ++++++++++++++++++++ >> mm/memcontrol.c | 150 +++++++++++++++++++++++++++++++++++++ >> 4 files changed, 252 insertions(+), 0 deletions(-) >> >> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h >> index 3d72e09..0d0363e 100644 >> --- a/include/linux/memcontrol.h >> +++ b/include/linux/memcontrol.h >> @@ -167,6 +167,11 @@ bool should_writeback_mem_cgroup_inode(struct inode *inode, >> struct writeback_control *wbc); >> bool mem_cgroups_over_bground_dirty_thresh(void); >> void mem_cgroup_writeback_done(void); >> +bool mem_cgroup_hierarchical_dirty_info(unsigned long sys_available_mem, >> + struct mem_cgroup *mem, >> + struct dirty_info *info); >> +void mem_cgroup_balance_dirty_pages(struct address_space *mapping, >> + unsigned long write_chunk); >> >> unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order, >> gfp_t gfp_mask, >> @@ -383,6 +388,19 @@ static inline void mem_cgroup_writeback_done(void) >> { >> } >> >> +static inline void mem_cgroup_balance_dirty_pages(struct address_space *mapping, >> + unsigned long write_chunk) >> +{ >> +} >> + >> +static inline bool >> +mem_cgroup_hierarchical_dirty_info(unsigned long sys_available_mem, >> + struct mem_cgroup *mem, >> + struct dirty_info *info) >> +{ >> + return false; >> +} >> + >> static inline >> unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order, >> gfp_t gfp_mask, >> diff --git a/include/linux/writeback.h b/include/linux/writeback.h >> index 66ec339..4f5c0d2 100644 >> --- a/include/linux/writeback.h >> +++ b/include/linux/writeback.h >> @@ -47,6 +47,7 @@ struct writeback_control { >> unsigned for_reclaim:1; /* Invoked from the page allocator */ >> unsigned range_cyclic:1; /* range_start is cyclic */ >> unsigned more_io:1; /* more io to be dispatched */ >> + unsigned for_cgroup:1; /* enable cgroup writeback */ >> unsigned shared_inodes:1; /* write inodes spanning cgroups */ >> }; >> >> diff --git a/include/trace/events/memcontrol.h b/include/trace/events/memcontrol.h >> index 326a66b..b42dae1 100644 >> --- a/include/trace/events/memcontrol.h >> +++ b/include/trace/events/memcontrol.h >> @@ -109,6 +109,89 @@ TRACE_EVENT(mem_cgroups_over_bground_dirty_thresh, >> __entry->first_id) >> ) >> >> +DECLARE_EVENT_CLASS(mem_cgroup_consider_writeback, >> + TP_PROTO(unsigned short css_id, >> + struct backing_dev_info *bdi, >> + unsigned long nr_reclaimable, >> + unsigned long thresh, >> + bool over_limit), >> + >> + TP_ARGS(css_id, bdi, nr_reclaimable, thresh, over_limit), >> + >> + TP_STRUCT__entry( >> + __field(unsigned short, css_id) >> + __field(struct backing_dev_info *, bdi) >> + __field(unsigned long, nr_reclaimable) >> + __field(unsigned long, thresh) >> + __field(bool, over_limit) >> + ), >> + >> + TP_fast_assign( >> + __entry->css_id = css_id; >> + __entry->bdi = bdi; >> + __entry->nr_reclaimable = nr_reclaimable; >> + __entry->thresh = thresh; >> + __entry->over_limit = over_limit; >> + ), >> + >> + TP_printk("css_id=%d bdi=%p nr_reclaimable=%ld thresh=%ld " >> + "over_limit=%d", __entry->css_id, __entry->bdi, >> + __entry->nr_reclaimable, __entry->thresh, __entry->over_limit) >> +) >> + >> +#define DEFINE_MEM_CGROUP_CONSIDER_WRITEBACK_EVENT(name) \ >> +DEFINE_EVENT(mem_cgroup_consider_writeback, name, \ >> + TP_PROTO(unsigned short id, \ >> + struct backing_dev_info *bdi, \ >> + unsigned long nr_reclaimable, \ >> + unsigned long thresh, \ >> + bool over_limit), \ >> + TP_ARGS(id, bdi, nr_reclaimable, thresh, over_limit) \ >> +) >> + >> +DEFINE_MEM_CGROUP_CONSIDER_WRITEBACK_EVENT(mem_cgroup_consider_bg_writeback); >> +DEFINE_MEM_CGROUP_CONSIDER_WRITEBACK_EVENT(mem_cgroup_consider_fg_writeback); >> + >> +TRACE_EVENT(mem_cgroup_fg_writeback, >> + TP_PROTO(unsigned long write_chunk, >> + struct writeback_control *wbc), >> + >> + TP_ARGS(write_chunk, wbc), >> + >> + TP_STRUCT__entry( >> + __field(unsigned long, write_chunk) >> + __field(long, wbc_to_write) >> + __field(bool, shared_inodes) >> + ), >> + >> + TP_fast_assign( >> + __entry->write_chunk = write_chunk; >> + __entry->wbc_to_write = wbc->nr_to_write; >> + __entry->shared_inodes = wbc->shared_inodes; >> + ), >> + >> + TP_printk("write_chunk=%ld nr_to_write=%ld shared_inodes=%d", >> + __entry->write_chunk, >> + __entry->wbc_to_write, >> + __entry->shared_inodes) >> +) >> + >> +TRACE_EVENT(mem_cgroup_enable_shared_writeback, >> + TP_PROTO(unsigned short css_id), >> + >> + TP_ARGS(css_id), >> + >> + TP_STRUCT__entry( >> + __field(unsigned short, css_id) >> + ), >> + >> + TP_fast_assign( >> + __entry->css_id = css_id; >> + ), >> + >> + TP_printk("enabling shared writeback for memcg %d", __entry->css_id) >> +) >> + >> #endif /* _TRACE_MEMCONTROL_H */ >> >> /* This part must be outside protection */ >> diff --git a/mm/memcontrol.c b/mm/memcontrol.c >> index a5b1794..17cb888 100644 >> --- a/mm/memcontrol.c >> +++ b/mm/memcontrol.c >> @@ -1622,6 +1622,156 @@ void mem_cgroup_writeback_done(void) >> } >> } >> >> +/* >> + * This routine must be called by processes which are generating dirty pages. >> + * It considers the dirty pages usage and thresholds of the current cgroup and >> + * (depending if hierarchical accounting is enabled) ancestral memcg. If any of >> + * the considered memcg are over their background dirty limit, then background >> + * writeback is queued. If any are over the foreground dirty limit then >> + * throttle the dirtying task while writing dirty data. The per-memcg dirty >> + * limits check by this routine are distinct from either the per-system, >> + * per-bdi, or per-task limits considered by balance_dirty_pages(). >> + */ >> +void mem_cgroup_balance_dirty_pages(struct address_space *mapping, >> + unsigned long write_chunk) >> +{ >> + struct backing_dev_info *bdi = mapping->backing_dev_info; >> + struct mem_cgroup *mem; >> + struct mem_cgroup *ref_mem; >> + struct dirty_info info; >> + unsigned long nr_reclaimable; >> + unsigned long sys_available_mem; >> + unsigned long pause = 1; >> + unsigned short id; >> + bool over; >> + bool shared_inodes; >> + >> + if (mem_cgroup_disabled()) >> + return; >> + >> + sys_available_mem = determine_dirtyable_memory(); >> + >> + /* reference the memcg so it is not deleted during this routine */ >> + rcu_read_lock(); >> + mem = mem_cgroup_from_task(current); >> + if (mem && mem_cgroup_is_root(mem)) >> + mem = NULL; >> + if (mem) >> + css_get(&mem->css); >> + rcu_read_unlock(); >> + ref_mem = mem; >> + >> + /* balance entire ancestry of current's mem. */ >> + for (; mem_cgroup_has_dirty_limit(mem); mem = parent_mem_cgroup(mem)) { >> + id = css_id(&mem->css); >> + >> + /* >> + * keep throttling and writing inode data so long as mem is over >> + * its dirty limit. >> + */ >> + for (shared_inodes = false; ; ) { >> + struct writeback_control wbc = { >> + .sync_mode = WB_SYNC_NONE, >> + .older_than_this = NULL, >> + .range_cyclic = 1, >> + .for_cgroup = 1, >> + .nr_to_write = write_chunk, >> + .shared_inodes = shared_inodes, >> + }; >> + >> + /* >> + * if mem is under dirty limit, then break from >> + * throttling loop. >> + */ >> + mem_cgroup_dirty_info(sys_available_mem, mem, &info); >> + nr_reclaimable = dirty_info_reclaimable(&info); >> + over = nr_reclaimable > info.dirty_thresh; >> + trace_mem_cgroup_consider_fg_writeback( >> + id, bdi, nr_reclaimable, info.dirty_thresh, >> + over); >> + if (!over) >> + break; >> + >> + mem_cgroup_mark_over_bg_thresh(mem); > > We are over the fg_thresh. > Then, why do you mark bg_thresh, too? It is possible for a cgroup to exceed its background limit without calling balance_dirty_pages() due to rate limiting in balance_dirty_pages_ratelimited_nr(). So this call to mem_cgroup_mark_over_bg_thresh() is needed to ensure that the cgroup is marked as over-bg-limit. The writeback_inodes_wb() call below writes the inodes owned by over-bg-limit memcg. This is not obvious. I will add a comment here explaining why marking over_bg_thresh in this situation. >> + writeback_inodes_wb(&bdi->wb, &wbc); >> + trace_mem_cgroup_fg_writeback(write_chunk, &wbc); >> + /* if no progress, then consider shared inodes */ >> + if ((wbc.nr_to_write == write_chunk) && >> + !shared_inodes) { >> + trace_mem_cgroup_enable_shared_writeback(id); >> + shared_inodes = true; > > I am not sure this is really right condition to punish shared inodes. > We requested wbc with async. If bdi was congested, isn't it possible > that we can't write anyting in this turn? > > If shared inodes are on different bdi, it would be effective but they > are on same bdi? > > If you assume that shared inode case is rare in memcg configuration > and it's right assumption, I don't have a concern about it. But I have > no idea. I am not sure if bdi congestion can cause a problem here. I don't think that bdi congestion would cause writeback to fail to submit IOs and decrement nr_to_write. But I could be wrong. There are other reasons that writeback_inodes_wb() may not make progress (e.g. if b_io has only one inode currently under writeback, then no progress may be made). To detect such cases would require adding more counters in the writeback code. I do not feel that it is necessary to avoid downshifting here into writing shared inodes. But I do see value in first trying to write non-shared inodes (as proposed in the patch). Shared inodes should be rare because their usage would further limit isolation offered by cgroups. I will add a comment to this section to clarify this. >> + } >> + >> + /* >> + * Sleep up to 100ms to throttle writer and wait for >> + * queued background I/O to complete. >> + */ >> + __set_current_state(TASK_UNINTERRUPTIBLE); >> + io_schedule_timeout(pause); >> + pause <<= 1; >> + if (pause > HZ / 10) >> + pause = HZ / 10; >> + } >> + >> + /* if mem is over background limit, then queue bg writeback */ >> + over = nr_reclaimable >= info.background_thresh; >> + trace_mem_cgroup_consider_bg_writeback( >> + id, bdi, nr_reclaimable, info.background_thresh, >> + over); >> + if (over) >> + mem_cgroup_queue_bg_writeback(mem, bdi); >> + } >> + >> + if (ref_mem) >> + css_put(&ref_mem->css); >> +} >> + >> +/* >> + * Return the dirty thresholds and usage for the mem (within the ancestral chain >> + * of @mem) closest to its dirty limit or the first memcg over its limit. > > dirty_info has return value 'bool'. > What's meaning? Of course, we can guess it by look the code. > But let's make user painful. > Please write down the menaing of return value, too. Good point. I will add more details to the comment. >> + * >> + * The check is not stable because the usage and limits can change asynchronous >> + * to this routine. >> + */ >> +bool mem_cgroup_hierarchical_dirty_info(unsigned long sys_available_mem, >> + struct mem_cgroup *mem, >> + struct dirty_info *info) >> +{ >> + unsigned long usage; >> + struct dirty_info uninitialized_var(cur_info); >> + >> + if (mem_cgroup_disabled()) >> + return false; >> + >> + info->nr_writeback = ULONG_MAX; /* invalid initial value */ >> + >> + /* walk up hierarchy enabled parents */ >> + for (; mem_cgroup_has_dirty_limit(mem); mem = parent_mem_cgroup(mem)) { >> + mem_cgroup_dirty_info(sys_available_mem, mem, &cur_info); >> + usage = dirty_info_reclaimable(&cur_info) + >> + cur_info.nr_writeback; >> + >> + /* if over limit, stop searching */ >> + if (usage >= cur_info.dirty_thresh) { >> + *info = cur_info; >> + break; >> + } >> + >> + /* >> + * Save dirty usage of mem closest to its limit if either: >> + * - mem is the first mem considered >> + * - mem dirty margin is smaller than last recorded one >> + */ >> + if ((info->nr_writeback == ULONG_MAX) || >> + (cur_info.dirty_thresh - usage) < >> + (info->dirty_thresh - >> + (dirty_info_reclaimable(info) + info->nr_writeback))) >> + *info = cur_info; >> + } >> + >> + return info->nr_writeback != ULONG_MAX; >> +} >> + >> static void mem_cgroup_start_move(struct mem_cgroup *mem) >> { >> int cpu; >> -- >> 1.7.3.1 >> -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757018Ab1FFSrz (ORCPT ); Mon, 6 Jun 2011 14:47:55 -0400 Received: from smtp-out.google.com ([216.239.44.51]:11183 "EHLO smtp-out.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756795Ab1FFSru (ORCPT ); Mon, 6 Jun 2011 14:47:50 -0400 DomainKey-Signature: a=rsa-sha1; s=beta; d=google.com; c=nofws; q=dns; h=from:to:cc:subject:references:date:message-id:user-agent: mime-version:content-type; b=MnyWM+Bq4BHk9FFsHkupuc74brakZYmm4d6ZA0K/lWtYZrs7Bu8J8QFRF1F8lXoUZ a2Ddw80bBxisodPtS4Jng== From: Greg Thelen To: Minchan Kim Cc: Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org, containers@lists.osdl.org, linux-fsdevel@vger.kernel.org, Andrea Righi , Balbir Singh , KAMEZAWA Hiroyuki , Daisuke Nishimura , Johannes Weiner , Ciju Rajan K , David Rientjes , Wu Fengguang , Vivek Goyal , Dave Chinner Subject: Re: [PATCH v8 10/12] memcg: create support routines for page-writeback References: <1307117538-14317-1-git-send-email-gthelen@google.com> <1307117538-14317-11-git-send-email-gthelen@google.com> <20110605031156.GB5914@barrios-laptop> Date: Mon, 06 Jun 2011 11:47:03 -0700 Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/23.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Minchan Kim writes: > Hi Greg, > > On Fri, Jun 03, 2011 at 09:12:16AM -0700, Greg Thelen wrote: >> Introduce memcg routines to assist in per-memcg dirty page management: >> >> - mem_cgroup_balance_dirty_pages() walks a memcg hierarchy comparing >> dirty memory usage against memcg foreground and background thresholds. >> If an over-background-threshold memcg is found, then per-memcg >> background writeback is queued. Per-memcg writeback differs from >> classic, non-memcg, per bdi writeback by setting the new >> writeback_control.for_cgroup bit. >> >> If an over-foreground-threshold memcg is found, then foreground >> writeout occurs. When performing foreground writeout, first consider >> inodes exclusive to the memcg. If unable to make enough progress, >> then consider inodes shared between memcg. Such cross-memcg inode >> sharing likely to be rare in situations that use per-cgroup memory >> isolation. The approach tries to handle the common (non-shared) >> case well without punishing well behaved (non-sharing) cgroups. >> As a last resort writeback shared inodes. >> >> This routine is used by balance_dirty_pages() in a later change. >> >> - mem_cgroup_hierarchical_dirty_info() returns the dirty memory usage >> and limits of the memcg closest to (or over) its dirty limit. This >> will be used by throttle_vm_writeout() in a latter change. >> >> Signed-off-by: Greg Thelen >> --- >> Changelog since v7: >> - Add more detail to commit description. >> >> - Declare the new writeback_control for_cgroup bit in this change, the >> first patch that uses the new field is first used. In -v7 the field >> was declared in a separate patch. >> >> include/linux/memcontrol.h | 18 +++++ >> include/linux/writeback.h | 1 + >> include/trace/events/memcontrol.h | 83 ++++++++++++++++++++ >> mm/memcontrol.c | 150 +++++++++++++++++++++++++++++++++++++ >> 4 files changed, 252 insertions(+), 0 deletions(-) >> >> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h >> index 3d72e09..0d0363e 100644 >> --- a/include/linux/memcontrol.h >> +++ b/include/linux/memcontrol.h >> @@ -167,6 +167,11 @@ bool should_writeback_mem_cgroup_inode(struct inode *inode, >> struct writeback_control *wbc); >> bool mem_cgroups_over_bground_dirty_thresh(void); >> void mem_cgroup_writeback_done(void); >> +bool mem_cgroup_hierarchical_dirty_info(unsigned long sys_available_mem, >> + struct mem_cgroup *mem, >> + struct dirty_info *info); >> +void mem_cgroup_balance_dirty_pages(struct address_space *mapping, >> + unsigned long write_chunk); >> >> unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order, >> gfp_t gfp_mask, >> @@ -383,6 +388,19 @@ static inline void mem_cgroup_writeback_done(void) >> { >> } >> >> +static inline void mem_cgroup_balance_dirty_pages(struct address_space *mapping, >> + unsigned long write_chunk) >> +{ >> +} >> + >> +static inline bool >> +mem_cgroup_hierarchical_dirty_info(unsigned long sys_available_mem, >> + struct mem_cgroup *mem, >> + struct dirty_info *info) >> +{ >> + return false; >> +} >> + >> static inline >> unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order, >> gfp_t gfp_mask, >> diff --git a/include/linux/writeback.h b/include/linux/writeback.h >> index 66ec339..4f5c0d2 100644 >> --- a/include/linux/writeback.h >> +++ b/include/linux/writeback.h >> @@ -47,6 +47,7 @@ struct writeback_control { >> unsigned for_reclaim:1; /* Invoked from the page allocator */ >> unsigned range_cyclic:1; /* range_start is cyclic */ >> unsigned more_io:1; /* more io to be dispatched */ >> + unsigned for_cgroup:1; /* enable cgroup writeback */ >> unsigned shared_inodes:1; /* write inodes spanning cgroups */ >> }; >> >> diff --git a/include/trace/events/memcontrol.h b/include/trace/events/memcontrol.h >> index 326a66b..b42dae1 100644 >> --- a/include/trace/events/memcontrol.h >> +++ b/include/trace/events/memcontrol.h >> @@ -109,6 +109,89 @@ TRACE_EVENT(mem_cgroups_over_bground_dirty_thresh, >> __entry->first_id) >> ) >> >> +DECLARE_EVENT_CLASS(mem_cgroup_consider_writeback, >> + TP_PROTO(unsigned short css_id, >> + struct backing_dev_info *bdi, >> + unsigned long nr_reclaimable, >> + unsigned long thresh, >> + bool over_limit), >> + >> + TP_ARGS(css_id, bdi, nr_reclaimable, thresh, over_limit), >> + >> + TP_STRUCT__entry( >> + __field(unsigned short, css_id) >> + __field(struct backing_dev_info *, bdi) >> + __field(unsigned long, nr_reclaimable) >> + __field(unsigned long, thresh) >> + __field(bool, over_limit) >> + ), >> + >> + TP_fast_assign( >> + __entry->css_id = css_id; >> + __entry->bdi = bdi; >> + __entry->nr_reclaimable = nr_reclaimable; >> + __entry->thresh = thresh; >> + __entry->over_limit = over_limit; >> + ), >> + >> + TP_printk("css_id=%d bdi=%p nr_reclaimable=%ld thresh=%ld " >> + "over_limit=%d", __entry->css_id, __entry->bdi, >> + __entry->nr_reclaimable, __entry->thresh, __entry->over_limit) >> +) >> + >> +#define DEFINE_MEM_CGROUP_CONSIDER_WRITEBACK_EVENT(name) \ >> +DEFINE_EVENT(mem_cgroup_consider_writeback, name, \ >> + TP_PROTO(unsigned short id, \ >> + struct backing_dev_info *bdi, \ >> + unsigned long nr_reclaimable, \ >> + unsigned long thresh, \ >> + bool over_limit), \ >> + TP_ARGS(id, bdi, nr_reclaimable, thresh, over_limit) \ >> +) >> + >> +DEFINE_MEM_CGROUP_CONSIDER_WRITEBACK_EVENT(mem_cgroup_consider_bg_writeback); >> +DEFINE_MEM_CGROUP_CONSIDER_WRITEBACK_EVENT(mem_cgroup_consider_fg_writeback); >> + >> +TRACE_EVENT(mem_cgroup_fg_writeback, >> + TP_PROTO(unsigned long write_chunk, >> + struct writeback_control *wbc), >> + >> + TP_ARGS(write_chunk, wbc), >> + >> + TP_STRUCT__entry( >> + __field(unsigned long, write_chunk) >> + __field(long, wbc_to_write) >> + __field(bool, shared_inodes) >> + ), >> + >> + TP_fast_assign( >> + __entry->write_chunk = write_chunk; >> + __entry->wbc_to_write = wbc->nr_to_write; >> + __entry->shared_inodes = wbc->shared_inodes; >> + ), >> + >> + TP_printk("write_chunk=%ld nr_to_write=%ld shared_inodes=%d", >> + __entry->write_chunk, >> + __entry->wbc_to_write, >> + __entry->shared_inodes) >> +) >> + >> +TRACE_EVENT(mem_cgroup_enable_shared_writeback, >> + TP_PROTO(unsigned short css_id), >> + >> + TP_ARGS(css_id), >> + >> + TP_STRUCT__entry( >> + __field(unsigned short, css_id) >> + ), >> + >> + TP_fast_assign( >> + __entry->css_id = css_id; >> + ), >> + >> + TP_printk("enabling shared writeback for memcg %d", __entry->css_id) >> +) >> + >> #endif /* _TRACE_MEMCONTROL_H */ >> >> /* This part must be outside protection */ >> diff --git a/mm/memcontrol.c b/mm/memcontrol.c >> index a5b1794..17cb888 100644 >> --- a/mm/memcontrol.c >> +++ b/mm/memcontrol.c >> @@ -1622,6 +1622,156 @@ void mem_cgroup_writeback_done(void) >> } >> } >> >> +/* >> + * This routine must be called by processes which are generating dirty pages. >> + * It considers the dirty pages usage and thresholds of the current cgroup and >> + * (depending if hierarchical accounting is enabled) ancestral memcg. If any of >> + * the considered memcg are over their background dirty limit, then background >> + * writeback is queued. If any are over the foreground dirty limit then >> + * throttle the dirtying task while writing dirty data. The per-memcg dirty >> + * limits check by this routine are distinct from either the per-system, >> + * per-bdi, or per-task limits considered by balance_dirty_pages(). >> + */ >> +void mem_cgroup_balance_dirty_pages(struct address_space *mapping, >> + unsigned long write_chunk) >> +{ >> + struct backing_dev_info *bdi = mapping->backing_dev_info; >> + struct mem_cgroup *mem; >> + struct mem_cgroup *ref_mem; >> + struct dirty_info info; >> + unsigned long nr_reclaimable; >> + unsigned long sys_available_mem; >> + unsigned long pause = 1; >> + unsigned short id; >> + bool over; >> + bool shared_inodes; >> + >> + if (mem_cgroup_disabled()) >> + return; >> + >> + sys_available_mem = determine_dirtyable_memory(); >> + >> + /* reference the memcg so it is not deleted during this routine */ >> + rcu_read_lock(); >> + mem = mem_cgroup_from_task(current); >> + if (mem && mem_cgroup_is_root(mem)) >> + mem = NULL; >> + if (mem) >> + css_get(&mem->css); >> + rcu_read_unlock(); >> + ref_mem = mem; >> + >> + /* balance entire ancestry of current's mem. */ >> + for (; mem_cgroup_has_dirty_limit(mem); mem = parent_mem_cgroup(mem)) { >> + id = css_id(&mem->css); >> + >> + /* >> + * keep throttling and writing inode data so long as mem is over >> + * its dirty limit. >> + */ >> + for (shared_inodes = false; ; ) { >> + struct writeback_control wbc = { >> + .sync_mode = WB_SYNC_NONE, >> + .older_than_this = NULL, >> + .range_cyclic = 1, >> + .for_cgroup = 1, >> + .nr_to_write = write_chunk, >> + .shared_inodes = shared_inodes, >> + }; >> + >> + /* >> + * if mem is under dirty limit, then break from >> + * throttling loop. >> + */ >> + mem_cgroup_dirty_info(sys_available_mem, mem, &info); >> + nr_reclaimable = dirty_info_reclaimable(&info); >> + over = nr_reclaimable > info.dirty_thresh; >> + trace_mem_cgroup_consider_fg_writeback( >> + id, bdi, nr_reclaimable, info.dirty_thresh, >> + over); >> + if (!over) >> + break; >> + >> + mem_cgroup_mark_over_bg_thresh(mem); > > We are over the fg_thresh. > Then, why do you mark bg_thresh, too? It is possible for a cgroup to exceed its background limit without calling balance_dirty_pages() due to rate limiting in balance_dirty_pages_ratelimited_nr(). So this call to mem_cgroup_mark_over_bg_thresh() is needed to ensure that the cgroup is marked as over-bg-limit. The writeback_inodes_wb() call below writes the inodes owned by over-bg-limit memcg. This is not obvious. I will add a comment here explaining why marking over_bg_thresh in this situation. >> + writeback_inodes_wb(&bdi->wb, &wbc); >> + trace_mem_cgroup_fg_writeback(write_chunk, &wbc); >> + /* if no progress, then consider shared inodes */ >> + if ((wbc.nr_to_write == write_chunk) && >> + !shared_inodes) { >> + trace_mem_cgroup_enable_shared_writeback(id); >> + shared_inodes = true; > > I am not sure this is really right condition to punish shared inodes. > We requested wbc with async. If bdi was congested, isn't it possible > that we can't write anyting in this turn? > > If shared inodes are on different bdi, it would be effective but they > are on same bdi? > > If you assume that shared inode case is rare in memcg configuration > and it's right assumption, I don't have a concern about it. But I have > no idea. I am not sure if bdi congestion can cause a problem here. I don't think that bdi congestion would cause writeback to fail to submit IOs and decrement nr_to_write. But I could be wrong. There are other reasons that writeback_inodes_wb() may not make progress (e.g. if b_io has only one inode currently under writeback, then no progress may be made). To detect such cases would require adding more counters in the writeback code. I do not feel that it is necessary to avoid downshifting here into writing shared inodes. But I do see value in first trying to write non-shared inodes (as proposed in the patch). Shared inodes should be rare because their usage would further limit isolation offered by cgroups. I will add a comment to this section to clarify this. >> + } >> + >> + /* >> + * Sleep up to 100ms to throttle writer and wait for >> + * queued background I/O to complete. >> + */ >> + __set_current_state(TASK_UNINTERRUPTIBLE); >> + io_schedule_timeout(pause); >> + pause <<= 1; >> + if (pause > HZ / 10) >> + pause = HZ / 10; >> + } >> + >> + /* if mem is over background limit, then queue bg writeback */ >> + over = nr_reclaimable >= info.background_thresh; >> + trace_mem_cgroup_consider_bg_writeback( >> + id, bdi, nr_reclaimable, info.background_thresh, >> + over); >> + if (over) >> + mem_cgroup_queue_bg_writeback(mem, bdi); >> + } >> + >> + if (ref_mem) >> + css_put(&ref_mem->css); >> +} >> + >> +/* >> + * Return the dirty thresholds and usage for the mem (within the ancestral chain >> + * of @mem) closest to its dirty limit or the first memcg over its limit. > > dirty_info has return value 'bool'. > What's meaning? Of course, we can guess it by look the code. > But let's make user painful. > Please write down the menaing of return value, too. Good point. I will add more details to the comment. >> + * >> + * The check is not stable because the usage and limits can change asynchronous >> + * to this routine. >> + */ >> +bool mem_cgroup_hierarchical_dirty_info(unsigned long sys_available_mem, >> + struct mem_cgroup *mem, >> + struct dirty_info *info) >> +{ >> + unsigned long usage; >> + struct dirty_info uninitialized_var(cur_info); >> + >> + if (mem_cgroup_disabled()) >> + return false; >> + >> + info->nr_writeback = ULONG_MAX; /* invalid initial value */ >> + >> + /* walk up hierarchy enabled parents */ >> + for (; mem_cgroup_has_dirty_limit(mem); mem = parent_mem_cgroup(mem)) { >> + mem_cgroup_dirty_info(sys_available_mem, mem, &cur_info); >> + usage = dirty_info_reclaimable(&cur_info) + >> + cur_info.nr_writeback; >> + >> + /* if over limit, stop searching */ >> + if (usage >= cur_info.dirty_thresh) { >> + *info = cur_info; >> + break; >> + } >> + >> + /* >> + * Save dirty usage of mem closest to its limit if either: >> + * - mem is the first mem considered >> + * - mem dirty margin is smaller than last recorded one >> + */ >> + if ((info->nr_writeback == ULONG_MAX) || >> + (cur_info.dirty_thresh - usage) < >> + (info->dirty_thresh - >> + (dirty_info_reclaimable(info) + info->nr_writeback))) >> + *info = cur_info; >> + } >> + >> + return info->nr_writeback != ULONG_MAX; >> +} >> + >> static void mem_cgroup_start_move(struct mem_cgroup *mem) >> { >> int cpu; >> -- >> 1.7.3.1 >>