linux-kernel - Re: [PATCH 2/3] staging: lowmemorykiller: count anon pages only when we have swap devices

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Message-ID: <CADAEsF8e2UgagtfZBjaK9J3ejnGFMmeznjzhm71ueJJ=rt0DJA@mail.gmail.com>
Date:	Fri, 1 Jul 2016 10:02:39 +0800
From:	Ganesh Mahendran <opensource.ganesh@...il.com>
To:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:	David Rientjes <rientjes@...gle.com>, devel@...verdev.osuosl.org,
	Greg KH <gregkh@...uxfoundation.org>, arve@...roid.com,
	riandrews@...roid.com, linux-kernel <linux-kernel@...r.kernel.org>,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Subject: Re: [PATCH 2/3] staging: lowmemorykiller: count anon pages only when
 we have swap devices

2016-06-23 16:42 GMT+08:00 Sergey Senozhatsky
<sergey.senozhatsky.work@...il.com>:
> On (06/22/16 11:27), Ganesh Mahendran wrote:
> [..]
>> > > Signed-off-by: Ganesh Mahendran <opensource.ganesh@...il.com>
>> > > ---
>> > >  drivers/staging/android/lowmemorykiller.c | 12 ++++++++----
>> > >  1 file changed, 8 insertions(+), 4 deletions(-)
>> > >
>> > > diff --git a/drivers/staging/android/lowmemorykiller.c b/drivers/staging/android/lowmemorykiller.c
>> > > index 6da9260..1d8de47 100644
>> > > --- a/drivers/staging/android/lowmemorykiller.c
>> > > +++ b/drivers/staging/android/lowmemorykiller.c
>> > > @@ -73,10 +73,14 @@ static unsigned long lowmem_deathpending_timeout;
>> > >  static unsigned long lowmem_count(struct shrinker *s,
>> > >                             struct shrink_control *sc)
>> > >  {
>> > > - return global_page_state(NR_ACTIVE_ANON) +
>> > > -         global_page_state(NR_ACTIVE_FILE) +
>> > > -         global_page_state(NR_INACTIVE_ANON) +
>> > > -         global_page_state(NR_INACTIVE_FILE);
>> > > + unsigned long freeable = global_page_state(NR_ACTIVE_FILE) +
>> > > +                         global_page_state(NR_INACTIVE_FILE);
>> > > +
>> > > + if (get_nr_swap_pages() > 0)
>> > > +         freeable += global_page_state(NR_ACTIVE_ANON) +
>> > > +                         global_page_state(NR_INACTIVE_ANON);
>> > > +
>> > > + return freeable;
>> > >  }
>> > >
>> > >  static unsigned long lowmem_scan(struct shrinker *s, struct shrink_control *sc)
>> >
>> > Shouldn't this be advertising the amount of memory that is freeable by
>> > killing the process with the highest priority oom_score_adj?  It's not
>> > legitimate to say it can free all anon and file memory if nothing is oom
>> > killable, so this function is wrong both originally and with your patched
>> > version.
>>
>> Yes, so should we just simply return 1 to make do_shrink_slab() go ahead?
>> Then lowmem_scan() will do the real job to scan all the process.
>
> hm, looking at ->scan (lowmem_scan) shouldn't it return SHRINK_STOP
> when it has nothing to free instead of 0?

Yes, you are right. It should return SHRINK_STOP.

>
>         -ss