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Wed, 11 May 2022 20:35:06 -0700 (PDT) Received: from localhost ([139.177.225.250]) by smtp.gmail.com with ESMTPSA id cp23-20020a17090afb9700b001cd4989fee1sm658198pjb.45.2022.05.11.20.35.05 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 11 May 2022 20:35:06 -0700 (PDT) Date: Thu, 12 May 2022 11:34:54 +0800 From: Muchun Song To: Mike Kravetz Cc: corbet@lwn.net, akpm@linux-foundation.org, mcgrof@kernel.org, keescook@chromium.org, yzaikin@google.com, osalvador@suse.de, david@redhat.com, masahiroy@kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, duanxiongchun@bytedance.com, smuchun@gmail.com Subject: Re: [PATCH v10 4/4] mm: hugetlb_vmemmap: add hugetlb_optimize_vmemmap sysctl Message-ID: References: <20220509062703.64249-1-songmuchun@bytedance.com> <20220509062703.64249-5-songmuchun@bytedance.com> <970166e0-f70e-dd2a-c764-af23a8425f87@oracle.com> <9d64809f-db8c-0a3e-1ae9-d4a8ab79041e@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, May 11, 2022 at 10:53:07AM -0700, Mike Kravetz wrote: > On 5/11/22 03:57, Muchun Song wrote: > > On Wed, May 11, 2022 at 05:45:57PM +0800, Muchun Song wrote: > >> On Tue, May 10, 2022 at 05:39:40PM -0700, Mike Kravetz wrote: > >>> On 5/10/22 14:30, Mike Kravetz wrote: > >>>> On 5/8/22 23:27, Muchun Song wrote: > >>>>> diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h > >>>>> index 029fb7e26504..917112661b5c 100644 > >>>>> --- a/include/linux/memory_hotplug.h > >>>>> +++ b/include/linux/memory_hotplug.h > >>>>> @@ -351,4 +351,13 @@ void arch_remove_linear_mapping(u64 start, u64 size); > >>>>> extern bool mhp_supports_memmap_on_memory(unsigned long size); > >>>>> #endif /* CONFIG_MEMORY_HOTPLUG */ > >>>>> > >>>>> +#ifdef CONFIG_MHP_MEMMAP_ON_MEMORY > >>>>> +bool mhp_memmap_on_memory(void); > >>>>> +#else > >>>>> +static inline bool mhp_memmap_on_memory(void) > >>>>> +{ > >>>>> + return false; > >>>>> +} > >>>>> +#endif > >>>>> + > >>>>> #endif /* __LINUX_MEMORY_HOTPLUG_H */ > >>>>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c > >>>>> index 8605d7eb7f5c..86158eb9da70 100644 > >>>>> --- a/mm/hugetlb.c > >>>>> +++ b/mm/hugetlb.c > >>>>> @@ -1617,6 +1617,9 @@ static DECLARE_WORK(free_hpage_work, free_hpage_workfn); > >>>>> > >>>>> static inline void flush_free_hpage_work(struct hstate *h) > >>>>> { > >>>>> + if (!hugetlb_optimize_vmemmap_enabled()) > >>>>> + return; > >>>>> + > >>>> > >>>> Hi Muchun, > >>>> > >>>> In v9 I was suggesting that we may be able to eliminate the static_branch_inc/dec from the vmemmap free/alloc paths. With this patch > >>>> I believe hugetlb_optimize_vmemmap_enabled() is really checking > >>>> 'has hugetlb vmemmap optimization been enabled' OR 'are there still vmemmap > >>>> optimized hugetlb pages in the system'. That may be confusing. > >>>> > >>> > >>> Sorry, I forgot about the use of hugetlb_optimize_vmemmap_enabled in > >>> page_fixed_fake_head. We need to know if there are any vmemmap optimized > >>> hugetlb pages in the system in this performance sensitive path. So, > >>> static_branch_inc/dec is indeed a good idea. > >>> > >> > >> Agree. > >> > >>> Please disregard my attempt below at removing static_branch_inc/dec. > >>> > >>> I still find the name hugetlb_optimize_vmemmap_enabled a bit confusing as > >>> it tests two conditions (enabled and pages in use). > >>> > >> > >> Right. It tests two conditions. > >> > >>> You have already 'open coded' just the check for enabled in the routine > >>> hugetlb_vmemmap_free with: > >>> > >>> READ_ONCE(vmemmap_optimize_mode) == VMEMMAP_OPTIMIZE_OFF > >>> > >>> How about having hugetlb_optimize_vmemmap_enabled() just check > >>> vmemmap_optimize_mode in a manner like above? Then rename > >> > >> I'm wondering is it necessary to do this? vmemmap_optimize_mode > >> is a internal state in hugetlb_vmemmap.c, at leaset now there is > >> no outside users who care about this. Open-coding may be not > >> an issue (I guess)? If one day someone cares it, maybe it it > >> the time to do this and rename hugetlb_optimize_vmemmap_enabled()? > >> I'm not against doing this, just expressing some of my thoughts. > >> What do you think, Mike? > >> > >>> hugetlb_optimize_vmemmap_enabled to something like: > >>> hugetlb_optimized_vmemmap_possible(). Sorry, I can think if a great name. > >>> > >> > >> At least I cannot come up with an appropriate name. > >> hugetlb_optimize_vmemmap_may_enabled()? It's not easy to come > >> up with a good name. > >> > > > > Instead of renaming, how about remove hugetlb_optimize_vmemmap_enabled() > > directly? I found there are only two places (mm/memory_hotplug.c and > > arch/arm64/mm/flush.c) except include/linux/page-flags.h where use this > > helper. > > > > In arch/arm64/mm/flush.c, we could replace it with > > > > if (PageHuge(page) && HPageVmemmapOptimized(compound_head(page))) > > > > In mm/memory_hotplug.c, I have a plan to remove it as well (I'll > > post them out after this patch merged). > > > > Finally, there is no outside users of it, we could remove it and squash > > it into page_fixed_fake_head(). What do you think this, Mike? > > That sounds good. > > Sorry for all the questions/suggestions around > hugetlb_optimize_vmemmap_enabled. It just caused me a little confusion > as it is providing information on two conditions. I wanted to prevent it > from causing confusion for others reading the code in the future. > Sorry for the confusing. I'll post the subsequent patches ASAP. > This patch as written is fine with plans for a follow up to remove > hugetlb_optimize_vmemmap_enabled. > > Reviewed-by: Mike Kravetz Thanks Mike.