From: Johannes Weiner <hannes@cmpxchg.org>
To: Michal Hocko <mhocko@kernel.org>
Cc: mateusznosek0@gmail.com, linux-mm@kvack.org,
linux-kernel@vger.kernel.org, akpm@linux-foundation.org
Subject: Re: [PATCH] mm/vmscan.c: Clean code by removing unnecessary assignment
Date: Fri, 20 Mar 2020 11:55:05 -0400 [thread overview]
Message-ID: <20200320155505.GA204561@cmpxchg.org> (raw)
In-Reply-To: <20200319171334.GK20800@dhcp22.suse.cz>
On Thu, Mar 19, 2020 at 06:13:34PM +0100, Michal Hocko wrote:
> It is usually preferable to Cc author of the code (added Johannes)
>
> On Thu 19-03-20 17:59:38, mateusznosek0@gmail.com wrote:
> > From: Mateusz Nosek <mateusznosek0@gmail.com>
> >
> > Previously 0 was assigned to 'sc->skipped_deactivate'. It could happen only
> > if 'sc->skipped_deactivate' was 0 so the assignment is unnecessary and can
> > be removed.
>
> The above wording was a bit hard to understdand for me. I would go with
> "
> sc->memcg_low_skipped resets skipped_deactivate to 0 but this is not
> needed as this code path is never reachable with skipped_deactivate != 0
> due to previous sc->skipped_deactivate branch.
> "
Yeah that sounds good.
> > Signed-off-by: Mateusz Nosek <mateusznosek0@gmail.com>
>
> The patch is correct. I am not sure it results in a better code though.
> I will defer to Johannes here. I suspect he simply wanted to express
> that skipped_deactivate should be always reset when retrying the direct
> reclaim. After this patch this could be lost in future changes so the
> code would be more subtle. But I am only guessing here.
It's a valid concern, but I think in this case specifically we're very
unlikely to change the ordering here - violate memory.low before going
after active pages of unprotected cgroups.
I indeed just kept it stupid: reset everything, then retry. But it
appears that the unnecessary assignment trips people up and wastes
their time, so I'm in favor of removing it.
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
next prev parent reply other threads:[~2020-03-20 15:55 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-19 16:59 [PATCH] mm/vmscan.c: Clean code by removing unnecessary assignment mateusznosek0
2020-03-19 17:13 ` Michal Hocko
2020-03-20 15:55 ` Johannes Weiner [this message]
-- strict thread matches above, loose matches on Subject: below --
2020-02-29 21:40 mateusznosek0
2020-03-01 0:11 ` Matthew Wilcox
2020-03-02 13:54 ` Wei Yang
2020-03-03 8:59 ` David Hildenbrand
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