Messages in this thread | | | Date | Fri, 10 Feb 2023 08:12:23 +0000 | From | "Yajun Deng" <> | Subject | Re: [PATCH v2] mm/page_alloc: optimize find_suitable_fallback() and fallbacks array |
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February 10, 2023 3:58 PM, "Vlastimil Babka" <vbabka@suse.cz> wrote:
> On 2/10/23 03:51, Yajun Deng wrote: > >> February 10, 2023 10:33 AM, "Yajun Deng" <yajun.deng@linux.dev> wrote: >> >>> February 10, 2023 10:14 AM, "Zi Yan" <ziy@nvidia.com> wrote: >> >> On 9 Feb 2023, at 20:57, Yajun Deng wrote: >> >> February 9, 2023 11:50 PM, "Zi Yan" <ziy@nvidia.com> wrote: >> >> On 9 Feb 2023, at 5:11, Yajun Deng wrote: >> There is no need to execute the next loop if it not return in the first >> loop. So add a break at the end of the loop. >> >> Can you explain why? If it is the case, MIGRATE_UNMOVABLE cannot fall back >> to MIGRATE_MOVABLE? And MIGRATE_MOVABLE cannot fall back to MIGRATE_UNMOVABLE? >> And MIGRATE_RECLAIMABLE cannot fall back to MIGRATE_MOVABLE? >> The return in the loop is only related to 'order', 'migratetype' and 'only_stealable' >> variables. Even if it execute the next loop, it can't change the result. So the loop >> can be broken if the first loop can't return. >> >> OK. Got it. Would the code below look better? >> >> for (i = 0; i < MIGRATE_PCPTYPES - 1 ; i++) { >> fallback_mt = fallbacks[migratetype][i]; >> if (free_area_empty(area, fallback_mt)) >> continue; >> } >> >> if (can_steal_fallback(order, migratetype)) >> *can_steal = true; >> >> if (!only_stealable || *can_steal) >> return fallback_mt; >> >> return -1; >>> Yes, I'll submit a v3 patch. >>> Thanks. >> >> I found a logical error in your code. It should be like this: >> >> for (i = 0; i < MIGRATE_PCPTYPES - 1 ; i++) { >> fallback_mt = fallbacks[migratetype][i]; >> if (!free_area_empty(area, fallback_mt)) >> break; >> } >> >> if (can_steal_fallback(order, migratetype)) >> *can_steal = true; >> >> if (!only_stealable || *can_steal) >> return fallback_mt; >> >> return -1; >> >> This code will modify the logic to the opposite. > > It's still wrong, IMHO. If all fallbacks have free_area_empty(), it will > return the last one and not -1. Also will set *can_steal in such case. >
Yes, you are right.
>> So can anyone tell me if I should use this code or the v2 patch? > > Once that bugs are fixed, the result will probably not look much better than > v2, so I don't mind keeping v2.
I agree with that.
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