From mboxrd@z Thu Jan 1 00:00:00 1970 From: KAMEZAWA Hiroyuki Subject: Re: [PATCH v8 10/12] memcg: create support routines for page-writeback Date: Wed, 8 Jun 2011 09:01:32 +0900 Message-ID: <20110608090132.ef9ccb91.kamezawa.hiroyu@jp.fujitsu.com> References: <1307117538-14317-1-git-send-email-gthelen@google.com> <1307117538-14317-11-git-send-email-gthelen@google.com> <20110607175056.83619c5f.kamezawa.hiroyu@jp.fujitsu.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: owner-linux-mm@kvack.org To: Greg Thelen 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 , Daisuke Nishimura , Minchan Kim , Johannes Weiner , Ciju Rajan K , David Rientjes , Wu Fengguang , Vivek Goyal , Dave Chinner List-Id: containers.vger.kernel.org On Tue, 07 Jun 2011 08:58:16 -0700 Greg Thelen wrote: > KAMEZAWA Hiroyuki writes: > > > On Fri, 3 Jun 2011 09:12:16 -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); > >> + > > > > Hmm, this sounds natural...but...don't we need to restart checking from ref_mem's > > dirty_ratio once we find an ancestor is over dirty_ratio and we slept ? > > > > Even if parent's dirty ratio comes to be clean state, children's may not. > > So, I think some "restart loop" jump after io_schedule_timeout(). > > > > Thanks, > > -Kame > > I do not think that we need to restart, but maybe you have a case in > mind that I am not considering. > > Example hierarchy: > root > A B > A1 A2 > A11 A12 A21 A22 > > Assume that mem_cgroup_balance_dirty_pages(A11), so ref_mem=A11. > > We start at A11 and walk up towards the root. If A11 is over limit, > then write A11 until under limit. Next check A1, if over limit then > write A1,A11,A12. Then check A. If A is over A limit, then we invoke > writeback on A* until A is under A limit. Are you concerned that while > performing writeback on A* that other tasks may push A1 over the A1 > limit? Such other task writers would also be calling > mem_cgroup_balance_dirty_pages() later. > Hm, ok. Could you add comments to explain the algorithm ? Thanks, -Kame -- 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 S932161Ab1FHAIi (ORCPT ); Tue, 7 Jun 2011 20:08:38 -0400 Received: from fgwmail5.fujitsu.co.jp ([192.51.44.35]:34605 "EHLO fgwmail5.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758734Ab1FHAIf (ORCPT ); Tue, 7 Jun 2011 20:08:35 -0400 X-SecurityPolicyCheck-FJ: OK by FujitsuOutboundMailChecker v1.3.1 Date: Wed, 8 Jun 2011 09:01:32 +0900 From: KAMEZAWA Hiroyuki To: Greg Thelen 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 , Daisuke Nishimura , Minchan Kim , 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 Message-Id: <20110608090132.ef9ccb91.kamezawa.hiroyu@jp.fujitsu.com> In-Reply-To: References: <1307117538-14317-1-git-send-email-gthelen@google.com> <1307117538-14317-11-git-send-email-gthelen@google.com> <20110607175056.83619c5f.kamezawa.hiroyu@jp.fujitsu.com> Organization: FUJITSU Co. LTD. X-Mailer: Sylpheed 3.1.0 (GTK+ 2.10.14; i686-pc-mingw32) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 07 Jun 2011 08:58:16 -0700 Greg Thelen wrote: > KAMEZAWA Hiroyuki writes: > > > On Fri, 3 Jun 2011 09:12:16 -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); > >> + > > > > Hmm, this sounds natural...but...don't we need to restart checking from ref_mem's > > dirty_ratio once we find an ancestor is over dirty_ratio and we slept ? > > > > Even if parent's dirty ratio comes to be clean state, children's may not. > > So, I think some "restart loop" jump after io_schedule_timeout(). > > > > Thanks, > > -Kame > > I do not think that we need to restart, but maybe you have a case in > mind that I am not considering. > > Example hierarchy: > root > A B > A1 A2 > A11 A12 A21 A22 > > Assume that mem_cgroup_balance_dirty_pages(A11), so ref_mem=A11. > > We start at A11 and walk up towards the root. If A11 is over limit, > then write A11 until under limit. Next check A1, if over limit then > write A1,A11,A12. Then check A. If A is over A limit, then we invoke > writeback on A* until A is under A limit. Are you concerned that while > performing writeback on A* that other tasks may push A1 over the A1 > limit? Such other task writers would also be calling > mem_cgroup_balance_dirty_pages() later. > Hm, ok. Could you add comments to explain the algorithm ? Thanks, -Kame