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From: Charan Teja Kalla <charante@codeaurora.org>
To: Vlastimil Babka <vbabka@suse.cz>,
	akpm@linux-foundation.org, nigupta@nvidia.com,
	hannes@cmpxchg.org, corbet@lwn.net, mcgrof@kernel.org,
	keescook@chromium.org, yzaikin@google.com, aarcange@redhat.com,
	cl@linux.com, xi.fengfei@h3c.com, mchehab+huawei@kernel.org,
	andrew.a.klychkov@gmail.com, dave.hansen@linux.intel.com,
	bhe@redhat.com, iamjoonsoo.kim@lge.com, mateusznosek0@gmail.com,
	sh_def@163.com, vinmenon@codeaurora.org
Cc: linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-mm@kvack.org, linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH v3 1/2] mm: compaction: support triggering of proactive compaction by user
Date: Thu, 17 Jun 2021 21:35:52 +0530	[thread overview]
Message-ID: <8d91a81b-09f3-e814-c9ce-16ff246ed359@codeaurora.org> (raw)
In-Reply-To: <0d516cfa-f41c-5ccc-26aa-67871f23dcd3@suse.cz>

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

  reply	other threads:[~2021-06-17 16:06 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-31 10:54 [PATCH V3 0/2] mm: compaction: proactive compaction trigger " Charan Teja Reddy
2021-05-31 10:54 ` [PATCH v3 1/2] mm: compaction: support triggering of proactive compaction " Charan Teja Reddy
2021-06-07 10:38   ` Charan Teja Kalla
2021-06-14 14:57     ` Charan Teja Kalla
2021-06-16 11:59   ` Vlastimil Babka
2021-06-17  7:30     ` Charan Teja Kalla
2021-06-17 14:37       ` Vlastimil Babka
2021-06-17 16:05         ` Charan Teja Kalla [this message]
2021-06-17 16:17           ` Vlastimil Babka
2021-05-31 10:54 ` [PATCH v3 2/2] mm: compaction: fix wakeup logic of proactive compaction Charan Teja Reddy

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