| Message ID | 20200319165938.23354-1-mateusznosek0@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | mm/vmscan.c: Clean code by removing unnecessary assignment | expand |
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. " > 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. > --- > mm/vmscan.c | 1 - > 1 file changed, 1 deletion(-) > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index dca623db51c8..453ff2abcb58 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -3093,7 +3093,6 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist, > if (sc->memcg_low_skipped) { > sc->priority = initial_priority; > sc->force_deactivate = 0; > - sc->skipped_deactivate = 0; > sc->memcg_low_reclaim = 1; > sc->memcg_low_skipped = 0; > goto retry; > -- > 2.17.1
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>
diff --git a/mm/vmscan.c b/mm/vmscan.c index dca623db51c8..453ff2abcb58 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -3093,7 +3093,6 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist, if (sc->memcg_low_skipped) { sc->priority = initial_priority; sc->force_deactivate = 0; - sc->skipped_deactivate = 0; sc->memcg_low_reclaim = 1; sc->memcg_low_skipped = 0; goto retry;