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AJvYcCXYv/aLgy8OZXcS1JWF3XyzgA8MtxRBlm/mYApgnic/NKA0uJg6kZ77ZJZTyOSckWtRuXxB008fwRhqhU+0U9qL708= X-Gm-Message-State: AOJu0Yyu7qPJF0IHAE3LnllZooMbIlOsFwN7ovsddFJUOuCNa2o/r6vo DWIx8yTzsQzRkpNShb32hbXl3kjoIQtEKWyWdSp58pjjxfvgTknk7E81xU1lVbNPWTmmoStbTUy aunFOzovBENafEZcveODMjdqYvyg= X-Google-Smtp-Source: AGHT+IHkU0BXuahEoyQX22QUsa04qtYpJiIPRQVXPHgYx4oh0LF1TIyS+xQ4LfVhA8LQQBA+IPKEb5wm1P/5s9AEo3A= X-Received: by 2002:a05:6358:5f1d:b0:1ac:f144:2b16 with SMTP id e5c5f4694b2df-1af3bababb6mr1497963255d.26.1722864833103; Mon, 05 Aug 2024 06:33:53 -0700 (PDT) MIME-Version: 1.0 References: <202408041602.caa0372-oliver.sang@intel.com> In-Reply-To: From: Pedro Falcato Date: Mon, 5 Aug 2024 14:33:41 +0100 Message-ID: Subject: Re: [linus:master] [mseal] 8be7258aad: stress-ng.pagemove.page_remaps_per_sec -4.4% regression To: Linus Torvalds Cc: kernel test robot , Jeff Xu , oe-lkp@lists.linux.dev, lkp@intel.com, linux-kernel@vger.kernel.org, Andrew Morton , Kees Cook , "Liam R. Howlett" , Dave Hansen , Greg Kroah-Hartman , Guenter Roeck , Jann Horn , Jeff Xu , Jonathan Corbet , Jorge Lucangeli Obes , Matthew Wilcox , Muhammad Usama Anjum , =?UTF-8?Q?Stephen_R=C3=B6ttger?= , Suren Baghdasaryan , Amer Al Shanawany , Javier Carrasco , Shuah Khan , linux-api@vger.kernel.org, linux-mm@kvack.org, ying.huang@intel.com, feng.tang@intel.com, fengwei.yin@intel.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 52924180002 X-Stat-Signature: 14aba4b6xe169r51s3g54utxwgi4u75m X-Rspamd-Server: rspam09 X-Rspam-User: X-HE-Tag: 1722864834-994489 X-HE-Meta: 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 dJH6+OIO QtZXNtZaYWxXTjBJuyxUGfh7geMr1suzgIVY+FdO2pBk+Pute8N3UokeBJcf3tSwy33WTJdeQoAmx7q7Kd8Ke+s/qw/839MAHQ9IMgVWksH9p0YVOH9+KpC5cP5HMCcaeIdPHYdmkSFJVpoDfyMBmu6OlolOi2LTCsEN6A5lDIsknkStlGH8IeFwVAcHUhj9xZ2VFCi01w0VlzqnF4LgyjrW498QkiXw9uXAdwFHmpXF14azCg2s/TffE/Nn4MluUi6g6TmElUP4sdB2IYsSDoo943IHf7sSqTFMaDk1Ztf+nXH7SqKTajF9A0aQKu03nfj+/8xfgj6I+8rJcNNoUESRCGy9Yo7ssUrp4PFN+84wk/wksNZR3w9/MJaW1I+ef3fZxc+pInQ0PohifL//pr9YIGnQn4VTI8RVyeQlhX8drIKBClxIs09kBquEg1FMnCFUdTy6p0beumyw= 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 Sun, Aug 4, 2024 at 9:33=E2=80=AFPM Linus Torvalds wrote: > > On Sun, 4 Aug 2024 at 01:59, kernel test robot wr= ote: > > > > kernel test robot noticed a -4.4% regression of stress-ng.pagemove.page= _remaps_per_sec on > > commit 8be7258aad44 ("mseal: add mseal syscall") > > Ok, it's basically just the vma walk in can_modify_mm(): > > > 1.06 +0.1 1.18 perf-profile.self.cycles-= pp.mas_next_slot > > 1.50 +0.5 1.97 perf-profile.self.cycles-= pp.mas_find > > 0.00 +1.4 1.35 perf-profile.self.cycles-= pp.can_modify_mm > > 3.13 +2.0 5.13 perf-profile.self.cycles-= pp.mas_walk > > and looks like it's two different pathways. We have __do_sys_mremap -> > mremap_to -> do_munmap -> do_vmi_munmap -> can_modify_mm for the > destination mapping, but we also have mremap_to() calling > can_modify_mm() directly for the source mapping. > > And then do_vmi_munmap() will do it's *own* vma_find() after having > done arch_unmap(). > > And do_munmap() will obviously do its own vma lookup as part of > calling vma_to_resize(). > > So it looks like a large portion of this regression is because the > mseal addition just ends up walking the vma list way too much. Can we rollback the upfront checks "funny business" and just call can_modify_vma directly in relevant places? I still don't believe in the partial mprotect/munmap "security risks" that were stated in the mseal thread (and these operations can already fail for many other reasons than mseal) :) I don't mind taking a look myself, just want to make sure I'm not stepping on anyone's toes here. --=20 Pedro