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[2003:d8:2f09:3f00:d228:bd67:7baa:d604]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-429c74ffb1esm92390395e9.5.2024.08.12.01.12.49 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 12 Aug 2024 01:12:50 -0700 (PDT) Message-ID: <66c4fcc5-47f6-438c-a73a-3af6e19c3200@redhat.com> Date: Mon, 12 Aug 2024 10:12:49 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [linus:master] [mm] c0bff412e6: stress-ng.clone.ops_per_sec -2.9% regression To: Mateusz Guzik , Yin Fengwei Cc: kernel test robot , Peter Xu , oe-lkp@lists.linux.dev, lkp@intel.com, linux-kernel@vger.kernel.org, Andrew Morton , Huacai Chen , Jason Gunthorpe , Matthew Wilcox , Nathan Chancellor , Ryan Roberts , WANG Xuerui , linux-mm@kvack.org, ying.huang@intel.com, feng.tang@intel.com References: <202407301049.5051dc19-oliver.sang@intel.com> <193e302c-4401-4756-a552-9f1e07ecedcf@redhat.com> <439265d8-e71e-41db-8a46-55366fdd334e@intel.com> <90477952-fde2-41d7-8ff4-2102c45e341d@redhat.com> <6uxnuf2gysgabyai2r77xrqegb7t7cc2dlzjz6upwsgwrnfk3x@cjj6on3wqm4x> <5a67c103-1d9d-440d-8bed-bbfa7d3ecf71@redhat.com> <5c0979a2-9a56-4284-82d2-42da62bda4a5@redhat.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 4D098C001F X-Stat-Signature: 8479n8qnjnjxiifb76qexp9wk76imc56 X-Rspam-User: X-HE-Tag: 1723450375-6879 X-HE-Meta: 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 dAGF9kdg 2vGCc9EXx15vuTfd3Px2vRcOE877+kRfrzvYkVvqCufbkLVU3rn5KvlQSOeAAdOmVJECHr/R2/2psZ+dbT8JBbqJlCCCSOFCECC7qb25hm4fwfwmee8gvGGTM6V+Lh3vQCYte+kPQEOcbYxh3V1PE1EmN+eqxWPDkwnuLGT5Znd9uJVRQ09zx6EgvvjFJSFKyE30B3TUNLBXnZkdd81rx/krMFgko4RHWDDYlCpOU+LXc346YpI5B2faN8NlIAE4PTH7afF4fZ+MeA72tOjs+KWpteqye8OQXsGcbYjtFULP5BVAZcxVa3ixHFUCdPDpwo5GuJLrbw0rIufgBoZ8RZzlzOelmJwWImrgROLfcehPtKLFAJLt6+wL973LvxeESyOG+Cx9k8Fhnr0nJ+mr/1ufDoaKUUNaQHcaGMNe4fts8miBfh/dVbu4YbbcOWbpEFDsS03Z5o2M1kCM= 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: List-Subscribe: List-Unsubscribe: On 12.08.24 06:49, Mateusz Guzik wrote: > On Mon, Aug 12, 2024 at 12:43:08PM +0800, Yin Fengwei wrote: >> Hi David, >> >> On 8/1/24 09:44, David Hildenbrand wrote: >>> On 01.08.24 15:37, Mateusz Guzik wrote: >>>> On Thu, Aug 1, 2024 at 3:34 PM David Hildenbrand >>>> wrote: >>>>> >>>>> On 01.08.24 15:30, Mateusz Guzik wrote: >>>>>> On Thu, Aug 01, 2024 at 08:49:27AM +0200, David Hildenbrand wrote: >>>>>>> Yes indeed. fork() can be extremely sensitive to each >>>>>>> added instruction. >>>>>>> >>>>>>> I even pointed out to Peter why I didn't add the >>>>>>> PageHuge check in there >>>>>>> originally [1]. >>>>>>> >>>>>>> "Well, and I didn't want to have runtime-hugetlb checks in >>>>>>> PageAnonExclusive code called on certainly-not-hugetlb code paths." >>>>>>> >>>>>>> >>>>>>> We now have to do a page_folio(page) and then test for hugetlb. >>>>>>> >>>>>>>       return folio_test_hugetlb(page_folio(page)); >>>>>>> >>>>>>> Nowadays, folio_test_hugetlb() will be faster than at >>>>>>> c0bff412e6 times, so >>>>>>> maybe at least part of the overhead is gone. >>>>>>> >>>>>> >>>>>> I'll note page_folio expands to a call to _compound_head. >>>>>> >>>>>> While _compound_head is declared as an inline, it ends up being big >>>>>> enough that the compiler decides to emit a real function instead and >>>>>> real func calls are not particularly cheap. >>>>>> >>>>>> I had a brief look with a profiler myself and for single-threaded usage >>>>>> the func is quite high up there, while it manages to get out with the >>>>>> first branch -- that is to say there is definitely performance lost for >>>>>> having a func call instead of an inlined branch. >>>>>> >>>>>> The routine is deinlined because of a call to page_fixed_fake_head, >>>>>> which itself is annotated with always_inline. >>>>>> >>>>>> This is of course patchable with minor shoveling. >>>>>> >>>>>> I did not go for it because stress-ng results were too unstable for me >>>>>> to confidently state win/loss. >>>>>> >>>>>> But should you want to whack the regression, this is what I would look >>>>>> into. >>>>>> >>>>> >>>>> This might improve it, at least for small folios I guess: >> Do you want us to test this change? Or you have further optimization >> ongoing? Thanks. > > I verified the thing below boots, I have no idea about performance. If > it helps it can be massaged later from style perspective. As quite a lot of setups already run with the vmemmap optimization enabled, I wonder how effective this would be (might need more fine tuning, did not look at the generated code): diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h index 085dd8dcbea2..7ddcdbd712ec 100644 --- a/include/linux/page-flags.h +++ b/include/linux/page-flags.h @@ -233,7 +233,7 @@ static __always_inline int page_is_fake_head(const struct page *page) return page_fixed_fake_head(page) != page; } -static inline unsigned long _compound_head(const struct page *page) +static __always_inline unsigned long _compound_head(const struct page *page) { unsigned long head = READ_ONCE(page->compound_head); -- Cheers, David / dhildenb