lkml.org 
[lkml]   [2021]   [Jun]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH v3 1/2] mm: compaction: support triggering of proactive compaction by user
From
Date
Thanks Vlastimil !!

On 6/17/2021 8:07 PM, Vlastimil Babka wrote:
> On 6/17/21 9:30 AM, Charan Teja Kalla wrote:
>> 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@codeaurora.org>
>>>> ---
>>>> changes in V2:
>>> You forgot to also summarize the changes. Please do in next version.
>>
>> 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 check whether to do non-proactive work is already guarded by
> kcompactd_work_requested(), which looks at pgdat->kcompactd_max_order and this
> is set by wakeup_kcompactd().
>
> So with a plain wakeup where we don't set pgdat->kcompactd_max_order will make
> it consider proactive work instead and we don't need another trigger variable
> AFAICS.

The wait_event/freezable_timeout() documentation says that:
* Returns:
* 0 if the @condition evaluated to %false after the @timeout elapsed,
or
* 1 if the @condition evaluated to %true after the @timeout elapsed,
* or the remaining jiffies (at least 1) if the @condition evaluated
* to %true before the @timeout elapsed.

which means the condition must be evaluated to true or timeout should be
elapsed for the function wait_event_freezable_timeout() to return.

Please check the macro implementation of __wait_event, where it will be
in for(;;) till the condition is evaluated to true or timeout happens.
#define __wait_event_freezable_timeout(wq_head, condition, timeout)

___wait_event(wq_head, ___wait_cond_timeout(condition),

TASK_INTERRUPTIBLE, 0, timeout,

__ret = freezable_schedule_timeout(__ret))

Thus the plain wakeup of kcompactd don't do the proactive compact work.
And so we should identify its wakeup for proactive work with a separate
flag.
>

--
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora
Forum, a Linux Foundation Collaborative Project

\
 
 \ /
  Last update: 2021-06-17 18:07    [W:0.064 / U:0.244 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site