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Date: Mon, 06 Jun 2011 11:51:54 -0700
From: Greg Thelen <gthelen@...gle.com>
To: Minchan Kim <minchan.kim@...il.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
linux-kernel@...r.kernel.org, linux-mm@...ck.org,
containers@...ts.osdl.org, linux-fsdevel@...r.kernel.org,
Andrea Righi <arighi@...eler.com>,
Balbir Singh <balbir@...ux.vnet.ibm.com>,
KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
Johannes Weiner <hannes@...xchg.org>,
Ciju Rajan K <ciju@...ux.vnet.ibm.com>,
David Rientjes <rientjes@...gle.com>,
Wu Fengguang <fengguang.wu@...el.com>,
Vivek Goyal <vgoyal@...hat.com>,
Dave Chinner <david@...morbit.com>
Subject: Re: [PATCH v8 11/12] writeback: make background writeback cgroup aware
Minchan Kim <minchan.kim@...il.com> writes:
> On Fri, Jun 03, 2011 at 09:12:17AM -0700, Greg Thelen wrote:
>> When the system is under background dirty memory threshold but a cgroup
>> is over its background dirty memory threshold, then only writeback
>> inodes associated with the over-limit cgroup(s).
>>
>> In addition to checking if the system dirty memory usage is over the
>> system background threshold, over_bground_thresh() also checks if any
>> cgroups are over their respective background dirty memory thresholds.
>> The writeback_control.for_cgroup field is set to distinguish between a
>> system and memcg overage.
>>
>> If performing cgroup writeback, move_expired_inodes() skips inodes that
>> do not contribute dirty pages to the cgroup being written back.
>>
>> After writing some pages, wb_writeback() will call
>> mem_cgroup_writeback_done() to update the set of over-bg-limits memcg.
>>
>> Signed-off-by: Greg Thelen <gthelen@...gle.com>
> Reviewed-by: Minchan Kim <minchan.kim@...il.com>
>
> There are some nitpicks at below.
>
>> ---
>> Changelog since v7:
>> - over_bground_thresh() now sets shared_inodes=1. In -v7 per memcg
>> background writeback did not, so it did not write pages of shared
>> inodes in background writeback. In the (potentially common) case
>> where the system dirty memory usage is below the system background
>> dirty threshold but at least one cgroup is over its background dirty
>> limit, then per memcg background writeback is queued for any
>> over-background-threshold cgroups. Background writeback should be
>> allowed to writeback shared inodes. The hope is that writing such
>> inodes has good chance of cleaning the inodes so they can transition
>> from shared to non-shared. Such a transition is good because then the
>> inode will remain unshared until it is written by multiple cgroup.
>> Non-shared inodes offer better isolation.
>
> Above comment should be in description.
Good point. I will add this to the commit description.
>>
>> fs/fs-writeback.c | 32 ++++++++++++++++++++++++--------
>> 1 files changed, 24 insertions(+), 8 deletions(-)
>>
>> diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
>> index 0174fcf..c0bfe62 100644
>> --- a/fs/fs-writeback.c
>> +++ b/fs/fs-writeback.c
>> @@ -256,14 +256,17 @@ static void move_expired_inodes(struct list_head *delaying_queue,
>> LIST_HEAD(tmp);
>> struct list_head *pos, *node;
>> struct super_block *sb = NULL;
>> - struct inode *inode;
>> + struct inode *inode, *tmp_inode;
>> int do_sb_sort = 0;
>>
>> - while (!list_empty(delaying_queue)) {
>> - inode = wb_inode(delaying_queue->prev);
>> + list_for_each_entry_safe_reverse(inode, tmp_inode, delaying_queue,
>> + i_wb_list) {
>> if (wbc->older_than_this &&
>> inode_dirtied_after(inode, *wbc->older_than_this))
>> break;
>> + if (wbc->for_cgroup &&
>> + !should_writeback_mem_cgroup_inode(inode, wbc))
>> + continue;
>> if (sb && sb != inode->i_sb)
>> do_sb_sort = 1;
>> sb = inode->i_sb;
>> @@ -614,14 +617,22 @@ void writeback_inodes_wb(struct bdi_writeback *wb,
>> */
>> #define MAX_WRITEBACK_PAGES 1024
>>
>> -static inline bool over_bground_thresh(void)
>> +static inline bool over_bground_thresh(struct bdi_writeback *wb,
>
> At present, wb isn't used.
> Do you remain it intentionally for using in future?
Good catch. At present, wb isn't used. I do not have plans to use it.
I will remove it.
>> + struct writeback_control *wbc)
>> {
>> unsigned long background_thresh, dirty_thresh;
>>
>> global_dirty_limits(&background_thresh, &dirty_thresh);
>>
>> - return (global_page_state(NR_FILE_DIRTY) +
>> - global_page_state(NR_UNSTABLE_NFS) > background_thresh);
>> + if (global_page_state(NR_FILE_DIRTY) +
>> + global_page_state(NR_UNSTABLE_NFS) > background_thresh) {
>> + wbc->for_cgroup = 0;
>> + return true;
>> + }
>> +
>> + wbc->for_cgroup = 1;
>> + wbc->shared_inodes = 1;
>> + return mem_cgroups_over_bground_dirty_thresh();
>> }
>>
>> /*
>> @@ -700,7 +711,7 @@ static long wb_writeback(struct bdi_writeback *wb,
>> * For background writeout, stop when we are below the
>> * background dirty threshold
>> */
>> - if (work->for_background && !over_bground_thresh())
>> + if (work->for_background && !over_bground_thresh(wb, &wbc))
>> break;
>>
>> if (work->for_kupdate || work->for_background) {
>> @@ -729,6 +740,9 @@ retry:
>> work->nr_pages -= write_chunk - wbc.nr_to_write;
>> wrote += write_chunk - wbc.nr_to_write;
>>
>> + if (write_chunk - wbc.nr_to_write > 0)
>> + mem_cgroup_writeback_done();
>> +
>> /*
>> * Did we write something? Try for more
>> *
>> @@ -809,7 +823,9 @@ static unsigned long get_nr_dirty_pages(void)
>>
>> static long wb_check_background_flush(struct bdi_writeback *wb)
>> {
>> - if (over_bground_thresh()) {
>> + struct writeback_control wbc;
>> +
>> + if (over_bground_thresh(wb, &wbc)) {
>>
>> struct wb_writeback_work work = {
>> .nr_pages = LONG_MAX,
>> --
>> 1.7.3.1
>>
--
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