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X-IronPort-AV: E=McAfee;i="6600,9927,10925"; a="426439106" X-IronPort-AV: E=Sophos;i="6.04,279,1695711600"; d="scan'208";a="426439106" Received: from orsmga008.jf.intel.com ([10.7.209.65]) by fmsmga101.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 15 Dec 2023 10:10:09 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6600,9927,10925"; a="803790500" X-IronPort-AV: E=Sophos;i="6.04,279,1695711600"; d="scan'208";a="803790500" Received: from jwaxmons-hp.amr.corp.intel.com (HELO [10.212.150.221]) ([10.212.150.221]) by orsmga008-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 15 Dec 2023 10:10:09 -0800 Message-ID: <99ce13b6-600d-411e-9dab-97a8ed166deb@intel.com> Date: Fri, 15 Dec 2023 10:10:08 -0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: mm/DAMON: Profiling enhancements for DAMON Content-Language: en-US To: Aravinda Prasad , damon@lists.linux.dev, linux-mm@kvack.org, sj@kernel.org, linux-kernel@vger.kernel.org Cc: s2322819@ed.ac.uk, sandeep4.kumar@intel.com, ying.huang@intel.com, dan.j.williams@intel.com, sreenivas.subramoney@intel.com, antti.kervinen@intel.com, alexander.kanevskiy@intel.com, Alan Nair References: <20231215074619.173787-1-aravinda.prasad@intel.com> From: Dave Hansen Autocrypt: addr=dave.hansen@intel.com; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: hyaw635iondrbqzhw3kqehsypyhw4xpp X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 496E514002B X-Rspam-User: X-HE-Tag: 1702663811-118013 X-HE-Meta: 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 b/ykJPpI nbYWUAf9lIZaJANHvaUhJ+rMPstxMmzQVhM6aebPuEe/gaLRjnlQukMokuybS8Ep+V6k8Hhck0/oozUnt5TqXKbffoya6JxpAFCSzy+/GQj292CZnYaDVMwDICuCgDaSBZC1GQS8KY2R36mAURUmaeqijIsuGppKAEpt9124tujanvhCUWTRWwMNUtw== 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 12/14/23 23:46, Aravinda Prasad wrote: > +static int damon_young_pmd(pmd_t *pmd, unsigned long addr, > + unsigned long next, struct mm_walk *walk) > +{ > + spinlock_t *ptl; > + struct damon_young_walk_private *priv = walk->private; > + > + if (!pmd_present(*pmd) || pmd_none(*pmd)) > + goto out; > + > + ptl = pmd_lock(walk->mm, pmd); > + if (pmd_young(*pmd) || mmu_notifier_test_young(walk->mm, addr)) > + priv->young = true; > + > + *priv->folio_sz = (1UL << PMD_SHIFT); > + spin_unlock(ptl); > +out: > + return 0; > +} There are a number of paired p*_present() and p_*none() checks in this patch. What is their function (especially pmd_none())? For instance, damon_young_pmd() gets called via the pagewalk infrastructure: > static int walk_pmd_range(pud_t *pud, unsigned long addr, unsigned long end, > struct mm_walk *walk) > { ... > next = pmd_addr_end(addr, end); > if (pmd_none(*pmd)) { ... > continue; > } ... > if (ops->pmd_entry) > err = ops->pmd_entry(pmd, addr, next, walk); I'd suggest taking a closer look at the code you are replacing and other mm_walk users to make sure the handlers are doing appropriate checks.