linux-kernel - RE: [PATCH V2] mm: compaction: support triggering of proactive compaction by user

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Message-ID: <BYAPR12MB3416727DB2BE2198C324124CD8259@BYAPR12MB3416.namprd12.prod.outlook.com>
Date:   Tue, 25 May 2021 20:35:37 +0000
From:   Nitin Gupta <nigupta@...dia.com>
To:     Charan Teja Reddy <charante@...eaurora.org>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "mcgrof@...nel.org" <mcgrof@...nel.org>,
        "keescook@...omium.org" <keescook@...omium.org>,
        "yzaikin@...gle.com" <yzaikin@...gle.com>,
        "vbabka@...e.cz" <vbabka@...e.cz>,
        "bhe@...hat.com" <bhe@...hat.com>,
        "mateusznosek0@...il.com" <mateusznosek0@...il.com>,
        "sh_def@....com" <sh_def@....com>,
        "iamjoonsoo.kim@....com" <iamjoonsoo.kim@....com>,
        "vinmenon@...eaurora.org" <vinmenon@...eaurora.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>
Subject: RE: [PATCH V2] mm: compaction: support triggering of proactive
 compaction by user



> -----Original Message-----
> From: charante=codeaurora.org@...codeaurora.org
> <charante=codeaurora.org@...codeaurora.org> On Behalf Of Charan Teja
> Reddy
> Sent: Tuesday, May 18, 2021 6:38 AM
> To: akpm@...ux-foundation.org; mcgrof@...nel.org;
> keescook@...omium.org; yzaikin@...gle.com; vbabka@...e.cz; Nitin
> Gupta <nigupta@...dia.com>; bhe@...hat.com;
> mateusznosek0@...il.com; sh_def@....com; iamjoonsoo.kim@....com;
> vinmenon@...eaurora.org
> Cc: linux-kernel@...r.kernel.org; linux-mm@...ck.org; linux-
> fsdevel@...r.kernel.org; Charan Teja Reddy <charante@...eaurora.org>
> Subject: [PATCH V2] mm: compaction: support triggering of proactive
> compaction by user
> 
> External email: Use caution opening links or attachments
> 
> 
> The proactive compaction[1] gets triggered for every 500msec and run
> compaction on the node for COMPACTION_HPAGE_ORDER (usually order-9)
> pages based on the value set to sysctl.compaction_proactiveness.
> Triggering the compaction for every 500msec in search of
> COMPACTION_HPAGE_ORDER pages is not needed for all applications,
> especially on the embedded system usecases which may have few MB's of
> RAM. Enabling the proactive compaction in its state will endup in running
> almost always on such systems.
> 

You can disable proactive compaction by setting sysctl.compaction_proactiveness to 0.


> Other side, proactive compaction can still be very much useful for getting a
> set of higher order pages in some controllable manner(controlled by using
> the sysctl.compaction_proactiveness). Thus on systems where enabling the
> proactive compaction always may proove not required, can trigger the same
> from user space on write to its sysctl interface. As an example, say app
> launcher decide to launch the memory heavy application which can be
> launched fast if it gets more higher order pages thus launcher can prepare
> the system in advance by triggering the proactive compaction from
> userspace.
> 

You can always do: echo 1 > /proc/sys/vm/compact_memory
On a small system, this should not take much time.

Hijacking proactive compaction for one-off compaction (say, before a large app launch)
does not sound right to me.

Thanks,
Nitin