linux-kernel - Re: [PATCH] mm/vmscan.c: no need to double-check if free pages are under high-watermark

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Date:   Sat, 26 Mar 2022 15:50:22 +0000
From:   Wei Yang <richard.weiyang@...il.com>
To:     Mel Gorman <mgorman@...hsingularity.net>
Cc:     DaeRo Lee <skseofh@...il.com>, akpm@...ux-foundation.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/vmscan.c: no need to double-check if free pages are
 under high-watermark

On Thu, Jan 06, 2022 at 12:57:58PM +0000, Mel Gorman wrote:
>On Thu, Jan 06, 2022 at 09:03:34PM +0900, DaeRo Lee wrote:
>> > > @@ -4355,7 +4355,7 @@ static enum zone_type kswapd_highest_zoneidx(pg_data_t *pgdat,
>> > >  static void kswapd_try_to_sleep(pg_data_t *pgdat, int alloc_order, int reclaim_order,
>> > >                               unsigned int highest_zoneidx)
>> > >  {
>> > > -     long remaining = 0;
>> > > +     long remaining = ~0;
>> > >       DEFINE_WAIT(wait);
>> > >
>> > >       if (freezing(current) || kthread_should_stop())
>> >
>> > While this does avoid calling prepare_kswapd_sleep() twice if the pgdat
>> > is balanced on the first try, it then does not restore the vmstat
>> > thresholds and doesn't call schedul() for kswapd to go to sleep.
>> 
>> I intended not to call prepare_kswapd_sleep() twice when the pgdat is NOT
>> balanced on the first try:)
>> 
>
>Stupid typo on my part.
>
>> > @@ -4406,11 +4412,11 @@ static void kswapd_try_to_sleep(pg_data_t *pgdat, int alloc_order, int reclaim_o
>> >         }
>> >
>> >         /*
>> > -        * After a short sleep, check if it was a premature sleep. If not, then
>> > -        * go fully to sleep until explicitly woken up.
>> > +        * If balanced to the high watermark, restore vmstat thresholds and
>> > +        * kswapd goes to sleep. If kswapd remains awake, account whether
>> > +        * the low or high watermark was hit quickly.
>> >          */
>> > -       if (!remaining &&
>> > -           prepare_kswapd_sleep(pgdat, reclaim_order, highest_zoneidx)) {
>> > +       if (balanced) {
>> >                 trace_mm_vmscan_kswapd_sleep(pgdat->node_id);
>> >
>> >                 /*
>> 
>> But, I think what you did is more readable and nice.
>> Thanks!
>> 
>
>Feel free to pick it up, rerun your tests to ensure it's behaving as
>expected and resend! Include something in the changelog about user-visible
>effects if any (or a note saying that it reduces unnecssary overhead)
>and resend with me added to the cc.
>

Hi, All

Seems this thread stops here. I don't see following patch and current upstream
doesn't include this change.

May I continue this? Of course, with author-ship from DaeRo Lee <skseofh@...il.com>.

Mel,

Would you mind suggesting some cases that I could do to see the effects from
this change? Such as the overhead or throughput? Or what cases you expect?


-- 
Wei Yang
Help you, Help me