linux-kernel - Re: [PATCH 1/2 v3] mm: vmscan: do not pass reclaimed slab to vmpressure

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Date:   Mon, 6 Feb 2017 17:01:06 +0530
From:   vinayak menon <vinayakm.list@...il.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Vinayak Menon <vinmenon@...eaurora.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>,
        mgorman@...hsingularity.net, vbabka@...e.cz,
        Rik van Riel <riel@...hat.com>, vdavydov.dev@...il.com,
        anton.vorontsov@...aro.org, Minchan Kim <minchan@...nel.org>,
        shashim@...eaurora.org, "linux-mm@...ck.org" <linux-mm@...ck.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2 v3] mm: vmscan: do not pass reclaimed slab to vmpressure

On Fri, Feb 3, 2017 at 8:29 PM, Michal Hocko <mhocko@...nel.org> wrote:
> On Fri 03-02-17 10:56:42, vinayak menon wrote:
>> On Thu, Feb 2, 2017 at 9:31 PM, Michal Hocko <mhocko@...nel.org> wrote:
>> >
>> > Why would you like to chose and kill a task when the slab reclaim can
>> > still make sufficient progres? Are you sure that the slab contribution
>> > to the stats makes all the above happening?
>> >
>> I agree that a task need not be killed if sufficient progress is made
>> in reclaiming
>> memory say from slab. But here it looks like we have an impact because of just
>> increasing the reclaimed without touching the scanned. It could be because of
>> disimilar costs or not adding adding cost. I agree that vmpressure is
>> only a reasonable
>> estimate which does not already include few other costs, but I am not
>> sure whether it is ok
>> to add another element which further increases that disparity.
>> We noticed this problem when moving from 3.18 to 4.4 kernel version. With the
>> same workload, the vmpressure events differ between 3.18 and 4.4 causing the
>> above mentioned problem. And with this patch on 4.4 we get the same results
>> as in 3,18. So the slab contribution to stats is making a difference.
>
> Please document that in the changelog along with description of the
> workload that is affected. Ideally also add some data from /proc/vmstat
> so that we can see the reclaim activity.

Sure, I will add these to the changelog.

Thanks,
Vinayak