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[2003:d8:2f09:3f00:d228:bd67:7baa:d604]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4290c77510asm185261545e9.33.2024.08.12.01.23.03 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 12 Aug 2024 01:23:04 -0700 (PDT) Message-ID: <206a16e3-3dfb-40f2-9785-389bc330e44d@redhat.com> Date: Mon, 12 Aug 2024 10:23:02 +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 Cc: Yin Fengwei , 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> <66c4fcc5-47f6-438c-a73a-3af6e19c3200@redhat.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Stat-Signature: 8daonmin1suxnnygmeeft5u3cnumpkpy X-Rspam-User: X-Rspamd-Queue-Id: AB4C1A0009 X-Rspamd-Server: rspam02 X-HE-Tag: 1723450990-911786 X-HE-Meta: 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 cWq5Adk9 gd19MSehZdrGoPFS8g2HoHQVbVWI+Gh0rswWM5XawGUl80F+kwf7oZK5EZLkaz31exA06O8oBaV5WBsvnVxSK1i9GPUMmLfwUK+1CQNcdsLiAszkecDJd6XpHJMyKd1kDu2prq4scH1iOj+e+xvvaKEsHIu0XFvkppT2BnRnGZFE0KHnABXvFIN/dphQWi5bmEyR7E4GYtkzS0/VZRS+JgPyjwSqEzelD6Ct42ZGXX/OxntDMrHaONyzh7JULOELJH/53BdqpKaISeGPy07mlZmMXYAORI7ypQhmgjLpXUvU7v0rb+yQNnDNz8XMdLRLm+AsFrsi2eXo35zC+8/+Q7hcd6dsJujmaJPGrCVRWuPwBXteVSRclfRG5NRmbZ58D/TnXc59zxrbtAYqoPdaPpG6/l1pVwwnpKBH4IFmiHxTxPHYdpiWQCYFnH6U3VyTvMxN8ALc5n4jNUtgQrUo8kJ24iQ== 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 10:18, Mateusz Guzik wrote: > On Mon, Aug 12, 2024 at 10:12 AM David Hildenbrand wrote: >> >> 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); >> >> > > Well one may need to justify it with bloat-o-meter which is why I did > not just straight up inline the entire thing. > > But if you are down to fight opposition of the sort I agree this is > the patch to benchmark. :) I spotted that we already to that for PageHead()/PageTail()/page_is_fake_head(). So we effectively force-inline it everywhere except into _compound_head() I think. But yeah, measuring the bloat would be a necessary exercise. -- Cheers, David / dhildenb