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Date: Thu, 17 Jun 2021 13:00:13 +0530
From: Charan Teja Kalla <charante@...eaurora.org>
To: Vlastimil Babka <vbabka@...e.cz>, akpm@...ux-foundation.org,
nigupta@...dia.com, hannes@...xchg.org, corbet@....net,
mcgrof@...nel.org, keescook@...omium.org, yzaikin@...gle.com,
aarcange@...hat.com, cl@...ux.com, xi.fengfei@....com,
mchehab+huawei@...nel.org, andrew.a.klychkov@...il.com,
dave.hansen@...ux.intel.com, bhe@...hat.com,
iamjoonsoo.kim@....com, mateusznosek0@...il.com, sh_def@....com,
vinmenon@...eaurora.org
Cc: linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-mm@...ck.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v3 1/2] mm: compaction: support triggering of proactive
compaction by user
Thanks Vlastimil for your inputs!!
On 6/16/2021 5:29 PM, Vlastimil Babka wrote:
>> This triggering of proactive compaction is done on a write to
>> sysctl.compaction_proactiveness by user.
>>
>> [1]https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit?id=facdaa917c4d5a376d09d25865f5a863f906234a
>>
>> Signed-off-by: Charan Teja Reddy <charante@...eaurora.org>
>> ---
>> changes in V2:
> You forgot to also summarize the changes. Please do in next version.
Sure. Will take care this in the next version.
>
>> */
>> unsigned int __read_mostly sysctl_compaction_proactiveness = 20;
>>
>> +int compaction_proactiveness_sysctl_handler(struct ctl_table *table, int write,
>> + void *buffer, size_t *length, loff_t *ppos)
>> +{
>> + int rc, nid;
>> +
>> + rc = proc_dointvec_minmax(table, write, buffer, length, ppos);
>> + if (rc)
>> + return rc;
>> +
>> + if (write && sysctl_compaction_proactiveness) {
>> + for_each_online_node(nid) {
>> + pg_data_t *pgdat = NODE_DATA(nid);
>> +
>> + if (pgdat->proactive_compact_trigger)
>> + continue;
>> +
>> + pgdat->proactive_compact_trigger = true;
> I don't like the new variable. I wish we could do without it. I understand this
> is added to ignore proactive_defer.
> We could instead expose proactive_defer in pgdat and reset it to 0 before wakeup
> (instead being a thread variable in kcompactd). But that would be racy with the
> decreases done by kcompactd.
> But I like the patch 2/2 and the idea could be extended to proactive_defer
> handling. If there's no proactive_defer, timeout is
> HPAGE_FRAG_CHECK_INTERVAL_MSEC. If kcompactd decides to defer, timeout would be
> HPAGE_FRAG_CHECK_INTERVAL_MSEC << COMPACT_MAX_DEFER_SHIFT. Thus, no more waking
> up just to decrease proactive_defer, we can then get rid of the counter. On
> writing new proactiveness just wake up and that's it, regardless of which
> timeout there was at the moment.
I think we can get rid off 'proactive_defer' thread variable with the
timeout approach you suggested. But it is still requires to have one
additional variable 'proactive_compact_trigger', which main purpose is
to decide if the kcompactd wakeup is for proactive compaction or not.
Please see below code:
if (wait_event_freezable_timeout() && !proactive_compact_trigger) {
// do the non-proactive work
continue
}
// do the proactive work
.................
Thus I feel that on writing new proactiveness, it is required to do
wakeup_kcomppactd() + set a flag that this wakeup is for proactive work.
Am I failed to get your point here?
> The only change is, if we get woken up to do non-proactive work, by
> wakeup_kcompactd(), the proactive_defer value would be now be effectively lost.
> I think it's OK as wakeup_kcompactd() means the condition of the zone changed
> substantionally anyway and carrying on with previous defer makes not much sense.
> What do you think?
Agree.
>
>> + wake_up_interruptible(&pgdat->kcompactd_wait);
>> + }
>> + }
>> +
>> + return 0;
>> +}
>> +
>> /*
>> * This is the entry point for compacting all nodes via
>> * /proc/sys/vm/compact_memory
>> @@ -2752,7 +2776,8 @@ void compaction_unregister_node(struct node *node)
>>
>> static inline bool kcompactd_work_requested(pg_data_t *pgdat)
>> {
>> - return pgdat->kcompactd_max_order > 0 || kthread_should_stop();
>> + return pgdat->kcompactd_max_order > 0 || kthread_should_stop() ||
>> + pgdat->proactive_compact_trigger;
>> }
>>
>> static bool kcompactd_node_suitable(pg_data_t *pgdat)
>> @@ -2905,7 +2930,8 @@ static int kcompactd(void *p)
>> trace_mm_compaction_kcompactd_sleep(pgdat->node_id);
>> if (wait_event_freezable_timeout(pgdat->kcompactd_wait,
>> kcompactd_work_requested(pgdat),
>> - msecs_to_jiffies(HPAGE_FRAG_CHECK_INTERVAL_MSEC))) {
>> + msecs_to_jiffies(HPAGE_FRAG_CHECK_INTERVAL_MSEC)) &&
>> + !pgdat->proactive_compact_trigger) {
>>
>> psi_memstall_enter(&pflags);
>> kcompactd_do_work(pgdat);
>> @@ -2917,10 +2943,20 @@ static int kcompactd(void *p)
>> if (should_proactive_compact_node(pgdat)) {
>> unsigned int prev_score, score;
>>
>> - if (proactive_defer) {
>> + /*
>> + * On wakeup of proactive compaction by sysctl
>> + * write, ignore the accumulated defer score.
>> + * Anyway, if the proactive compaction didn't
>> + * make any progress for the new value, it will
>> + * be further deferred by 2^COMPACT_MAX_DEFER_SHIFT
>> + * times.
>> + */
>> + if (proactive_defer &&
>> + !pgdat->proactive_compact_trigger) {
>> proactive_defer--;
>> continue;
>> }
>> +
>> prev_score = fragmentation_score_node(pgdat);
>> proactive_compact_node(pgdat);
>> score = fragmentation_score_node(pgdat);
>> @@ -2931,6 +2967,8 @@ static int kcompactd(void *p)
>> proactive_defer = score < prev_score ?
>> 0 : 1 << COMPACT_MAX_DEFER_SHIFT;
>> }
>> + if (pgdat->proactive_compact_trigger)
>> + pgdat->proactive_compact_trigger = false;
>> }
>>
>> return 0;
--
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