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From: Yajun Deng In-Reply-To: <23302f67-eb69-265a-ab2d-9c55715e2843@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Stat-Signature: ch9q3kqn5wsgt617fjau4pbwor51tpn8 X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: D8BF080018 X-HE-Tag: 1697451457-681737 X-HE-Meta: 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 G0NgnGxB uppJd2FU7TeWqKsKKnc1tl/FjCHFhEhmZmQRbauOLpd+g3XgHurPYWBLEZgIstOzfkc4OM6s560H7vQMMhgXCU0X3gUncDl681Uh0nmNQ18IRr2BdElDqc9wtCMscynoPEqxm7ES1/WCd1OsN4MPyCLl5n2jvsri/M5NMAesTgwhMneWLFoQC4r2f0yHzrfCQqrmJ X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 2023/10/16 16:36, David Hildenbrand wrote: > On 16.10.23 10:32, Yajun Deng wrote: >> >> On 2023/10/16 16:16, David Hildenbrand wrote: >>> On 16.10.23 10:10, Yajun Deng wrote: >>>> >>>> On 2023/10/16 14:33, Mike Rapoport wrote: >>>>> On Fri, Oct 13, 2023 at 05:29:19PM +0800, Yajun Deng wrote: >>>>>> On 2023/10/13 16:48, Mike Rapoport wrote: >>>>>>> On Thu, Oct 12, 2023 at 05:53:22PM +0800, Yajun Deng wrote: >>>>>>>> On 2023/10/12 17:23, David Hildenbrand wrote: >>>>>>>>> On 10.10.23 04:31, Yajun Deng wrote: >>>>>>>>>> On 2023/10/8 16:57, Yajun Deng wrote: >>>>>>>>>>>> That looks wrong. if the page count would by pure luck be 0 >>>>>>>>>>>> already for hotplugged memory, you wouldn't clear the reserved >>>>>>>>>>>> flag. >>>>>>>>>>>> >>>>>>>>>>>> These changes make me a bit nervous. >>>>>>>>>>> Is 'if (page_count(page) || PageReserved(page))' be safer? Or >>>>>>>>>>> do I >>>>>>>>>>> need to do something else? >>>>>>>>>>> >>>>>>>>>> How about the following if statement? But it needs to add more >>>>>>>>>> patch >>>>>>>>>> like v1 ([PATCH 2/4] mm: Introduce MEMINIT_LATE context). >>>>>>>>>> >>>>>>>>>> It'll be safer, but more complex. Please comment... >>>>>>>>>> >>>>>>>>>>         if (context != MEMINIT_EARLY || (page_count(page) || >>>>>>>>>> PageReserved(page)) { >>>>>>>>>> >>>>>>>>> Ideally we could make initialization only depend on the context, >>>>>>>>> and not >>>>>>>>> check for count or the reserved flag. >>>>>>>>> >>>>>>>> This link is v1, >>>>>>>> https://lore.kernel.org/all/20230922070923.355656-1-yajun.deng@linux.dev/ >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>>> If we could make initialization only depend on the context, I'll >>>>>>>> modify it >>>>>>>> based on v1. >>>>>>> Although ~20% improvement looks impressive, this is only >>>>>>> optimization of a >>>>>>> fraction of the boot time, and realistically, how much 56 msec >>>>>>> saves from >>>>>>> the total boot time when you boot a machine with 190G of RAM? >>>>>> There are a lot of factors that can affect the total boot time. 56 >>>>>> msec >>>>>> saves may be insignificant. >>>>>> >>>>>> But if we look at the boot log, we'll see there's a significant >>>>>> time jump. >>>>>> >>>>>> before: >>>>>> >>>>>> [    0.250334] ACPI: PM-Timer IO Port: 0x508 >>>>>> [    0.618994] Memory: 173413056K/199884452K available (18440K >>>>>> kernel code, >>>>>> >>>>>> after: >>>>>> >>>>>> [    0.260229] software IO TLB: area num 32. >>>>>> [    0.563497] Memory: 173413056K/199884452K available (18440K >>>>>> kernel code, >>>>>> Memory: >>>>>> Memory initialization is time consuming in the boot log. >>>>> You just confirmed that 56 msec is insignificant and then you send >>>>> again >>>>> the improvement of ~60 msec in memory initialization. >>>>> >>>>> What does this improvement gain in percentage of total boot time? >>>> >>>> >>>> before: >>>> >>>> [   10.692708] Run /init as init process >>>> >>>> >>>> after: >>>> >>>> [   10.666290] Run /init as init process >>>> >>>> >>>> About 0.25%. The total boot time is variable, depending on how many >>>> drivers need to be initialized. >>>> >>>> >>>>>>> I still think the improvement does not justify the churn, added >>>>>>> complexity >>>>>>> and special casing of different code paths of initialization of >>>>>>> struct pages. >>>>>> >>>>>> Because there is a loop, if the order is MAX_ORDER, the loop will >>>>>> run 1024 >>>>>> times. The following 'if' would be safer: >>>>>> >>>>>> 'if (context != MEMINIT_EARLY || (page_count(page) || >> >>>>>> PageReserved(page)) >>>>>> {' >>>>> No, it will not. >>>>> >>>>> As the matter of fact any condition here won't be 'safer' because it >>>>> makes >>>>> the code more complex and less maintainable. >>>>> Any future change in __free_pages_core() or one of it's callers will >>>>> have >>>>> to reason what will happen with that condition after the change. >>>> >>>> >>>> To avoid introducing MEMINIT_LATE context and make code simpler. This >>>> might be a better option. >>>> >>>> if (page_count(page) || PageReserved(page)) >>> >>> I'll have to side with Mike here; this change might not be worth it. >>> >> >> Okay, I got it. Thanks! > > IMHO instead of adding more checks to that code we should try to unify > that handling such that we can just remove it. As expressed, at least > from the memory hotplug perspective there are still reasons why we > need that; I can provide some guidance on how to eventually achieve > that, but it might end up in a bit of work ... Yes, we can't remove it right now. If we want to do that, we have to clean up rely on page count and PageReserved first. > > Anyhow, thanks for bringing up that topic; it reminded me that I still > have pending cleanups to not rely on PageReserved on the memory > hotplug path. >