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Wed, 11 May 2022 02:46:09 -0700 (PDT) Received: from localhost ([139.177.225.234]) by smtp.gmail.com with ESMTPSA id g23-20020a170902869700b0015ec44d25dasm1297219plo.235.2022.05.11.02.46.09 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 11 May 2022 02:46:09 -0700 (PDT) Date: Wed, 11 May 2022 17:45:57 +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: <9d64809f-db8c-0a3e-1ae9-d4a8ab79041e@oracle.com> Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org 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. Thanks.