Messages in this thread |  | | Subject | Re: [v2 PATCH] mm: vmscan: correct nr_reclaimed for THP | From | Yang Shi <> | Date | Tue, 14 May 2019 13:44:35 -0700 |
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On 5/13/19 11:20 PM, Michal Hocko wrote: > On Mon 13-05-19 21:36:59, Yang Shi wrote: >> On Mon, May 13, 2019 at 2:45 PM Michal Hocko <mhocko@kernel.org> wrote: >>> On Mon 13-05-19 14:09:59, Yang Shi wrote: >>> [...] >>>> I think we can just account 512 base pages for nr_scanned for >>>> isolate_lru_pages() to make the counters sane since PGSCAN_KSWAPD/DIRECT >>>> just use it. >>>> >>>> And, sc->nr_scanned should be accounted as 512 base pages too otherwise we >>>> may have nr_scanned < nr_to_reclaim all the time to result in false-negative >>>> for priority raise and something else wrong (e.g. wrong vmpressure). >>> Be careful. nr_scanned is used as a pressure indicator to slab shrinking >>> AFAIR. Maybe this is ok but it really begs for much more explaining >> I don't know why my company mailbox didn't receive this email, so I >> replied with my personal email. >> >> It is not used to double slab pressure any more since commit >> 9092c71bb724 ("mm: use sc->priority for slab shrink targets"). It uses >> sc->priority to determine the pressure for slab shrinking now. >> >> So, I think we can just remove that "double slab pressure" code. It is >> not used actually and looks confusing now. Actually, the "double slab >> pressure" does something opposite. The extra inc to sc->nr_scanned >> just prevents from raising sc->priority. > I have to get in sync with the recent changes. I am aware there were > some patches floating around but I didn't get to review them. I was > trying to point out that nr_scanned used to have a side effect to be > careful about. If it doesn't have anymore then this is getting much more > easier of course. Please document everything in the changelog.
Thanks for reminding. Yes, I remembered nr_scanned would double slab pressure. But, when I inspected into the code yesterday, it turns out it is not true anymore. I will run some test to make sure it doesn't introduce regression.
BTW, I noticed the counter of memory reclaim is not correct with THP swap on vanilla kernel, please see the below:
pgsteal_kswapd 21435 pgsteal_direct 26573329 pgscan_kswapd 3514 pgscan_direct 14417775
pgsteal is always greater than pgscan, my patch could fix the problem.
Anyway, I will elaborate these in the commit log.
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